5 1 2 meiosis and variation (1)

8/12/2019 5 1 2 Meiosis and Variation (1)

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1. (a) (i) A gene controlling coat colour in cats is sex linked. The two alleles of thisgene are black and orange. When both are present the coat colour is calledtortoiseshell.

Define the following terms:

gene........................................................................................................

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allele .......................................................................................................

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(ii) "xplain wh# there are no male tortoiseshell cats.

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Macmillan Academy 1


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Two pure breeding strains of snapdragon$ a garden plant$ were obtained. %nestrain had red flowers and the other had white flowers. The two strains werecrossed #ielding &'plants all with pink flowers. The &'were then interbred to

produce &plants with the following colours:

red 62

pink 131

white 67

The following h#pothesis was proposed:

Flower colour is controlled by a single gene with two codominant alleles.

(b) omplete the genetic diagram to explain this cross. se the following s#mbols torepresent the alleles:

Cr= red, C

w= white

*arental phenot#pes: red flowers x white flowers

*arental genot#pes: .................................... ........................................

+ametes: .................................... ........................................

&'genot#pes: ..................................................................................................

&'phenot#pes: ................................................................................................

+ametes: ........................................................................................................

&genot#pes: ..................................................................................................

&phenot#pes: ................................................................................................

"xpected &phenot#pic ratio:.........................................................................

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Macmillan Academy 2


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(c) A chi-suared () test is carried out on the experimental data to determine

whether the h#pothesis is supported.

(i) omplete the table below b# calculating the expected numbers.

&phenot#pe obser/ed numbers expected numbers

red ,

pink '0'

white ,1

total ,2 ,2

[0!

The statistic is calculated in the following wa#:

( )=

expected

expectedobserved 2

2 = sum of ...

(ii) alculate the /alue of for the abo/e data. 3how #our working.

/alue 4 ................................................................................................

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(iii) The critical /alue of for this t#pe of in/estigation with two degrees of

freedom is 5.66'.

"xplain whether #our answer to (b (iisupports the h#pothesis.

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[Total ', marks!

Macmillan Academy 3


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2. *henot#pe is influenced b# genetic and en/ironmental factors.

Describe oneexample of how the environment influences phenot#pe.

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[Total marks!

3. 7eproduction in seahorses$ Hippocampus$ is unusual as it is the male rather than thefemale that becomes pregnant. The male has a brood pouch located on its tail. Thelarger the male the larger the pouch. The female transfers unfertilised eggs into thepouch. The larger the female the more eggs are produced that can be transferred tothe brood pouch. The male releases sperm onto the eggs and the# are fertilised. Themale carries the de/eloping brood for a period of se/eral weeks until he finall# gi/esbirth.

7esearch into seahorse populations has re/ealed the following.

8 The# are monogamous. A male and female remain together for the whole matingseason.

8 Within a population$ mates are selected b# si9e. arge females mate with largemales and small females mate with small males.

8 &ew intermediate si9ed indi/iduals are produced and the# ha/e a low sur/i/alrate.

Macmillan Academy 4


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Two different species of seahorse are found in the coastal regions shown in the figurebelow. The ranges of these two seahorse species o/erlap in man# areas of thesewaters.

n i t e d 3 t a t e s o f A m e r i c a

+ u l f o f ; e x i c o

< i p p o c a m p u s e r e c t u s

A c t u a l s i 9 e : ' c m

! e "

a r i b b e a n

A t l a n t i c

% c e a n

< i p p o c a m p u s 9 o s t e r a e

A c t u a l s i 9 e : c m

The two seahorse silhouettes are not drawn to scale.

= A + >ones$ ;ale pregnanc# and the formation of seahorse species = ?nstitute of @iolog#$ 22

(a) (i) Bame the t#pe of speciation that occurs when there is no geographicalbarrier to gene flow.

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Macmillan Academy 5


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(ii) "xplain how the figure abo/e supports the h#pothesis that the t#pe ofspeciation named in (i) has occurred in seahorses.

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The t#pe of natural selection that can produce the t#pe of speciation that has occurredin seahorses is known as disrupti/e selection. This is where the extreme phenot#pesare more likel# to sur/i/e and reproduce than the intermediate phenot#pes.

(b) "xplain how disrupti/e selection occurs in seahorse populations.

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(c) ?n terms of reproducti/e potential$ explain wh# it is beneficial for large females tomate with large$ rather than small$ males.

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[Total C marks!

Macmillan Academy 6


7/63

#.

During interphase preceding meiosis$ each chromosome replicates itself and becomestwo chromatids oined at the centromere. These identical chromatids are known as

sister chromatids. During the first di/ision of meiosis$ pairing of homologouschromosomes takes place. The structure formed is called a bi/alent. When paired inthis wa# non-sister chromatids from the two chromosomes exchange segments ofgenetic material b# breaking and reoining.

(i) 3tate the name gi/en to the exchange of segments of chromatids b# breakingand reoining.

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(ii) Bame the stage of the first di/ision of meiosis when this exchange of segmentsoccurs.

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(iii) Describe the genetic difference between sister and non-sister chromatids.

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[Total 0 marks!

$. The following figure represents a pair of homologous chromosomes at the beginning ofthe first di/ision of meiosis. The loci of two genes are shown$ and both genes ha/e twoalleles.

% %

r r & &

' '

Macmillan Academy


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omplete the diagram below to show the four possible gametes formed at the end ofmeiosis. se the same letters as in the figure abo/e.

[Total: marks!

6. A student carried out a genetic in/estigation with fruit flies$ !rosophila melanogaster.Two characteristics were obser/ed$ bod# colour and wing shape. The student had thefollowing information:

8 the characteristics were controlled b# separate genes carried on separatechromosomes

8 gre# bod# colour was dominant to black bod# colour

8 normal wing shape was dominant to bent wing shape.

The student carried out a cross between a fl# hetero")ousfor both gre# bod# colourand normal wing shape and a fl# with a black bod# and bent wing. The numbers andphenot#pes of the offspring were as follows:

gre# bod# and normal wing C0

black bod# and normal wing C5

gre# bod# and bent wing 1C

black bod# and bent wing 1

Macmillan Academy "


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(i) omplete the genetic diagram to explain this cross. se the following s#mbols torepresent the alleles:

* = )re" bod" co+our, = b+ck bod" co+our

- = norm+ win) shpe, b = bent win) shpe

*arental phenot#pes: gre# bod# E normal wing x black bod# E bent wing

*arental genot#pes: ..................................... ..........................................

+ametes: ..................................................... ..........................................

%ffspring genot#pes: .......................................................................................

%ffspring phenot#pes: .....................................................................................

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*henot#pic ratio: .............................................................................................

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The student concluded that the results showed that independent assortment hadtaken place.

To determine whether this conclusion is ustified a chi-suared test () can be

carried out on the experimental data.

(ii) omplete the table below b# calculating the expected numbers.

offspring obser/ed numbers expected numbersgre# bod# E normal wing C0black bod# E normal wing C5

gre# bod# E bent wing 1Cblack bod# E bent wing 1

total 02 02

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Macmillan Academy #


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(iii) The /alue is calculated in the following wa#:

( )

=

expected

expectedobser/ed

2 where FG4 H sum of IJ

alculate the /alue for the abo/e data. 3how #our working.

/alue 4 ..........................................................

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(i/) The critical /alue of for this t#pe of in/estigation with three degrees of freedom

is 1.C.

"xplain whether #our answer to (c) (iii) supports the studentJs conclusion.

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[Total 6 marks!

Macmillan Academy 1$


11/63

7. "xplain wh# +,*D deficienc# is more common in areas where malaria occursregularl#.

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[Total: 0 marks!

. (a) White eghorn domesticated chickens carr# a dominant allele$ /$ that inhibitsfeather pigmentation. @irds homo9#gous for the recessi/e allele$ i$ ha/epigmented plumage$ pro/ided that the# carr# the dominant allele$ C$ of a gene formelanin production.

Bame the interaction between alleles / and C.

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(b) Allele i codes for a protein that is essential for normal production of melanin. ?ncomparison with i$ allele / has a 6 base pair insertion in its DBA.

"xplain how such an insertion could alter the expression of the gene.

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Macmillan Academy 11


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(c) 7ed >unglefowl are the wild ancestors of domesticated chickens.

unglefowland the 01offspring$ all of which were white$ interbred to gi/e an 02generation.

The 02generation included both white and pigmented birds.

(i) 3tate the genot#pes at the /i and Cc loci of the parental and 01

generations.

parental phenot#pes: White eghorn K 7ed >unglefowl

parental genot#pes: ........................ ........................

01genot#pe: ...............................................................

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(ii) 3tate the ratio of phenot#pes expected in the 02generation.

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[Total C marks!

. "xplain wh# breeders of domesticated chickens consider it important to maintain apopulation of 7ed >unglefowl.

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[Total marks!



13/63

1. 7ed >unglefowl are the wild ancestors of domesticated chickens.

unglefowl and the01offspring$ all of which were white$ interbred to gi/e an 02generation. The 02

generation included both white and pigmented birds.

The 02birds were di/ided into ten groups$ each with slightl# different percentages of

white and pigmented birds. "ach bird was examined at inter/als to assess an# damageto its feathers caused b# feather-pecking b# other birds in the group.

The results of the in/estigation are shown in the figure below.

C

' 2

,

2

' C 2p e r c e n t a g e o f w h i t e b i r d s

i n g r o u p

d a m a g e t o

f e a t h e r s

c a u s e d b #

f e a t h e r - p e c k i n g

a r b i t r a r # u n i t s

,

C

' 2

p i g m e n t e d

,

2' C 2

p e r c e n t a g e o f p i g m e n t e d b i r d s

i n g r o u p

d a m a g e t o

f e a t h e r s

c a u s e d b #

f e a t h e r - p e c k i n g

a r b i t r a r # u n i t s

,

w h i t ek e # t o p h e n o t # p e s o f b i r d s :



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Describe the effect on feather-pecking of changes in the percentage of each phenot#pein a group.

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[Total 0 marks!

11. About '2L of the coffee consumed in the world has been processed to remo/ecaffeine. The decaffeination process also remo/es some of the fla/ouring compoundsso$ since '6C1$ researchers at the coffee gene bank in @ra9il ha/e been tr#ing toproduce suitable /arieties of caffeine-free coffee plants.

The most commonl# culti/ated species of coffee plant$ %o&&ea arabica$ has a narrowgenetic di/ersit#. ?t is a tetraploid with chromosomes (n 4 ) and almost alwa#sself-pollinates.

All attempts to start a selecti/e breeding programme to transfer the caffeine-freepropert# of a diploid wild species of coffee from ;adagascar (n 4 ) to %. arabicaha/e failed.

(i) "xplain briefl# wh# selecti/e breeding is carried out.

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(ii) "xplain wh# %. arabica has a narrow genetic di/ersit#.

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(iii) 3uggest wh# attempts at interbreeding %. arabica with the wild species from;adagascar ha/e failed.

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[Total , marks!



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12. *lants from a different species of coffee plant$ %. canephora$ ha/e been geneticall#engineered to ha/e a low caffeine content b# suppressing the acti/it# of caffeines#nthase.

Describe one ad/antage and one disad/antage of producing coffee plants with inacti/ecaffeine s#nthase b# genetic engineering rather than b# selecti/e breeding.

ad/antage ................................................................................................................

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disad/antage ...........................................................................................................

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[Total marks!

13. 3elf-incompatibilit# in '. rhoeas is controlled b# a locus$ 4$ coding for proteins in thepollen and stigmas of the flowers. The locus has a large number of alleles and e/ensmall populations ha/e a large number of different genot#pes.

*ollen is reected when its haploid genot#pe is the same as either of the two alleles ofthe diploid stigma of the recipient plant. *ollen with a different allele is compatible.

(i) omplete the table to show whether pollen is accepted ( ) or reected ( ) b#each stigma.

genot#pe ofhaploid pollen

genot#pe ofdiploid stigma

pollenaccepted ( ) or

reected ( )

41 4142

42 4142

41 4243

42 4243

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(ii) 3tate$ with reson$ whether the /ariation shown is continuous or discontinuous/ariation.

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[Total , marks!

1#. The diagram below shows the life c#cles of two organisms$ *and -.

a d u l t

( n )

# o u n g o r g a n i s m

( n )

a d u l t

( n )

9 # g o t e

( n )

g a m e t e

( n )

g a m e t e

( n )

or)nism * or)nism -

Macmillan Academy 1


18/63

(i) Bame the t#pe of reproduction taking place in the life c#cle of organism *.

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(ii) "xplain wh# it is important that the gametes in the life c#cle of organism -contain the haploid number of chromosomes.

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1$. oat colour in rabbits is determined b# a single gene which has four separate alleles.The gene is notsex linked.

8 The allele for agouti colour$ C*$ is dominant to all the other alleles.

8 The allele for albino$ C$ is recessi/e to all the other alleles.

8 The allele for chinchilla$ CCh

$ is dominant to the


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16. ?n the wild$ rabbits ha/e a high reproducti/e rate.


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(b) ?n an in/estigation into the genes on chromosome of the tomato genome$pollen from a pure-bred plant with green lea/es and smooth-surfaced fruit wastransferred to flowers of a plant with mottled green and #ellow lea/es and hair#(so-called HpeachJ) fruit. All the &'generation had green lea/es and smooth fruit.

Describe briefl# how a plant breeder ensures that the offspring produced areon+"from the desired cross.

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(c) &our different test crosses$ *to $ were then made between &'plants and pure-

bred plants with mottled lea/es and HpeachJ fruit. The phenot#pes of 52 offspringof each of the crosses were recorded and are shown in the table below.

phenot#pes of offspring of test crosses

cross green lea/es andsmooth fruit

green lea/es andHpeachJ fruit

mottled lea/esand smooth fruit

mottled lea/esand HpeachJ fruit

* 0 0 2

- ' 0 0 0

C ', 5 5

, 'C

total C '1 '5 C,

(i) 3uggest onereason wh#$ in the table abo/e$ the numbers of plants withgreen lea/es and smooth fruit is not the same in each of the crosses*to .

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(ii) The percentage cross o/er /alue is calculated as

'22offspringofnumbertotal

offspringtrecombinanofnumber

sing the information in the table abo/e$ calculate the percentage crosso/er /alue between the loci for leaf colour and fruit surface texture. 3how#our working.

Answer 4 ..................................................... L[!

(iii) se annotated diagrams of tomato chromosome to explain the results ofthe test crosses shown in the table.

se the s#mbols *for the leaf colour alleles and -bfor the fruit surfacetexture alleles.

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[Total: '5 marks!

1. (i) %utline the principle of selecti/e breeding.

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(ii) "xplain the use of progen# testing in selecti/e breeding.

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[Total , marks!

1. ?n this uestion$ one mark is a/ailable for the ualit# of spelling$ punctuation andgrammar.

?n '656$ a breeding colon# of '22 female and 02 male 3iberian foxes was establishedin 7ussia. &or the next 5 #ears$ the# were selecti/el# bred for onetrait onl#: that oflack of aggression to humans (tameness).

@# the end of 22$ the beha/iour and appearance of the selecti/el# bred foxesdiffered from wild foxes in the following wa#s:

8 their fur had white patches

8 their mu99les were shorter

8 some had flopp# ears and curl# tails

8 the# whimpered to attract human attention$ wagged their tails and licked thehumanJs hand.

Describe how selecti/e breeding of animals is carried out ndexplain how selecti/el#breeding for onetrait ma# result in man# differences between selecti/el# bred and wildanimals.

[C!

Mualit# of Written ommunication ['!

[Total 6 marks!



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2. The numbers of musk deer ha/e hal/ed in ten #ears. ?n parts of hina the populationsha/e reached /er# low numbers. These populations are also widel# separated.

%utline the possible conseuences of this separation on the populations of musk deer.

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[Total marks!



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21. The following figure shows e/ents leading to the formation of homologous pairs inmeiosis.

a x i a l

e l e m e n t

t w o s i s t e r c h r o m a t i d s

a x i a l

e l e m e n t p r o t e i n s i s t e r

c h r o m a t id s o f o n e

c h r o m o s o m e

n o n - s i s t e r

c h r o m a t id s

D B A r e p + i c , t e s d u r i n g

i n t e r p h a s e f o r m i n g t w os i s t e r c h r o m a t i d s .

@ o t h s i s t e r c h r o m a t id sa t t a c h t o a p r o t e i n r o d

c a l l e d t h e a x i a l e l e m e n t .

T h e a x i a l e l e m e n t s o f

h o m o l o g o u s c h r o m o s o m e sc o m e t o g e t h e r i n t h e

f o r m a t i o n o f a h o m o l o g o u sp a i r ( b i / a l e n t ) .

(i) "xplain wh# the DBA in two sister chromatids is identical.

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(ii) "xplain wh# the DBA in two sister chromatids in metaphase ma# no longer beidentical.

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(iii) 3uggest wh# axial elements are necessar# in meiosis.

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[Total , marks!



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22. The figure below shows se/eral stages in the life c#cle of the water flea$ !aphnia.

C

A

B

z y g o t e s E

m e i o s i s

m i t o s i s

m i t o s i s

m i t o s i sf e m a l eg a m e t e s

m a l eg a m e t e s

e g g s

g r o w t h

m e i o s i s

f e m a l eD

f a v o u r a b l e c o n d i t i o n s

?n fa/ourable conditions$ all the indi/iduals in a population are females$ *.

These females produce eggs$ -$ b# mitosiswhich de/elop into further females.

?n unfa/ourable conditions$ eggs are produced b# meiosisand de/elop withoutfertilisation into either males$ C$ or females$ .

+ametes are produced b# mitosisfrom Cand .

The resultant 9#gotes$ $ de/elop a protecti/e case which enables them tosur/i/e unfa/ourable conditions.

When fa/ourable conditions return$ these 9#gotes de/elop into #oung females.

(i) 3tate which of the stages$ *to $ contain indi/iduals with the diploid number ofchromosomes.

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(ii) "xplain wh# the females in stage *show greater /ariation than the females instage .

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(iii) "xplain wh# gametes are produced b# mitosis from males Cand females .

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[Total 5 marks!

23. ?n this uestion$ one mark is a/ailable for the ualit# of use and organisation ofscientific terms.

Describe the beha/iour of chromosomes during meiosiswhich results in genetic/ariation among !aphnia populations.

[1!


[Total C marks!

Macmillan Academy 2


28/63

2#. The human A@% blood groups are A$ @$ A@ and %. The# are determined b# a single

gene with multiple alleles. /*and /

-alleles are codominant$ but both these alleles are

dominant to the /8

allele.

?n a maternit# ward$ the identities of four babies became accidentall# mixed up. TheA@% blood groups of the babies were disco/ered to be %$ A$ @ and A@. The A@%blood groups of the four sets of parents were determined and are shown in the tablebelow.

omplete the table to match each bab# to its parents b# indicating:

the parental genot#pes$ using the s#mbols /*$ /

-and /

8N

the blood group of the bab# which belongs to each set of parents.

parental blood groups parental genot#pes bab# blood group

% and %

A@ and %

A and %

A@ and A

[Total marks!

Macmillan Academy 2"


29/63

2$. Two species of monke#flower$ Mimulus$ ha/e pink anthoc#anin pigment in their flowerpetals.

?n both species$ two alleles of a gene$ *$ control the acti/it# of another gene

responsible for the production of a second pigment$ a carotenoid. The dominant allele$*$ pre/ents carotenoid production so that the flowers show onl# their pink anthoc#aninpigment.

&lowers containing both anthoc#anin and carotenoid pigments are red in colour.

(a) (i) Describe the interaction between gene *and the gene responsible forcarotenoid production.

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(ii) "xplain wh# flower colour in Mimulus is an example of discontinuous/ariation.

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Macmillan Academy 2#


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(b) Wild t#pe M. lewisii ha/e the genot#pe **and ha/e pink flowers that arepollinated b# bumblebees.

Wild t#pe M. cardinalis ha/e the genot#pe and ha/e red flowers that are

pollinated b# hummingbirds.

The two species were interbred to in/estigate the role of gene *in attractingpollinators to the flowers. Alleles *and were exchanged between the twospecies in the selecti/e breeding programme shown in the figure below.

s t e p 1 w i l d t # p e M . l e w i s i i( g e n o t # p e w i t h p i n k f l o w e r s )* *

w i l d t # p e M . c a r d i n a l i s( g e n o t # p e w i t h r e d f l o w e r s ), ,

h # b r i d

( g e n o t # p e * , w i t h p i n k f l o w e r s )

s t e p 2 + i n e 1b a c k c r o s s e d f o r s e / e r a l g e n e r a t i o n s

w i t h M . l e w i s i i

+ i n e 2

b a c k c r o s s e d f o r s e / e r a l g e n e r a t i o n s

w i t h M . c a r d i n a l i s

s t e p 3 s e l f - p o l l i n a t e d a n d g e n o t # p e , ,

p l a n t s w i t h r e d f l o w e r s s e l e c t e d

g e n o t # p e p l a n t s w i t h p i n k f l o w e r s* 9

s e l e c t e d

(i) 3tate twopractical precautions that the plant breeder could take to be surethat the plants produced in step 1were h#brids.

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(ii) "xplain wh#$ in step 2$ the h#brids were backcrossed for se/eralgenerations to one or other of the parent species.

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(iii) 3tate wh# the plants in +ine 1were self-pollinated in step 3.

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(c) The number and t#pe of pollinators /isiting different coloured flowers were thenrecorded. The results are shown in the table below.

plant species genot#pe flower colour

number ofpollinator /isits per hour

bumblebee hummingbird

wild t#pe M. lewisii ** pink '5 2

selecti/el# bred M. lewisii red 0

wild t#pe M. cardinalis red 2 '62

selecti/el# bred M. cardinalis * pink '' '12

omment on the effect on pollinators of selecti/el# breeding allele into M.lewisii and allele *into M. cardinalis.

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[Total '5 marks!



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26. A gene$ %'$ affecting muscle mass and fat deposition in pigs has been identified incrosses between domesticated pigs and wild boars. ;ost "uropean domesticated pigscarr# the dominant allele$ %$ but wild boar populations are homo9#gous recessi/e. The%'gene codes for a protein growth factor$ ?+&.

The transcription of the gene in skeletal and cardiac muscle was measured in pigletswith %%and ''genot#pes at three and sixteen weeks after birth. The results areshown in the figure below.

' . 5

' . 2 2

2 . 1 5

2 . 5 2

2 . 5

20 ' , 0 ' ,

a g e o f p i g l e t E w e e k s

t r a n s c r i p t i o no f ? + & g e n e E a r b i t r a r # u n i t s

g e n o t # p e % %

g e n o t # p e ' '

s k e l e t a l m u s c l e

c a r d i a c m u s c l e

k e # :



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sing the information abo/e$ compare the transcription of the ?+& gene in piglets with%%and ''genot#pes.

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[Total marks!

27. (a) An infection b# the bacterium$ 'seudomonas aeruginosa$ ma# be in the form ofseparate bacterial cells or of a HbiofilmJ. A biofilm is a la#er of bacteria growing ona surface$ attached to one another b# pol#mers of glucose. ?nfections in the formof biofilms are difficult to control b# antibiotics.

3uggest wh# infections in the form of biofilms are more difficult to control b#antibiotics than those caused b# separate bacterial cells.

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(b) The sensiti/it# of two strains of '. aeruginosa to three commonl# used antibiotics(*$ -and C) was measured when the bacteria were grown in suspension and inbiofilms. The results are shown in the table below.

lowest concentration ofantibiotic needed to kill

bacteria E Og cmP0

* - C

strin 1bacteria insuspension

C 2

strin 1bacteria in

biofilm

22 522 52

strin 2bacteria insuspension

C 2

strin 2bacteria inbiofilm

5 ,2 ,

ompare the sensiti/it# of bacterial strins 1and 2to the three antibiotics when

grown in suspension and in biofilms.

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(c) A gene has been identified in '. aeruginosa which is expressed on+"when cellsgrow in biofilms. The gene codes for an en9#me which is needed for thes#nthesis of pol#mers of glucose$ called glucans$ which are secreted b# thebacteria. 3trains ' and ha/e different alleles of this gene.

"xplain how the difference in sensiti/it# to antibiotics of strains ' and couldha/e arisen.

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(d) Describe briefl# how resistance to an antibiotic ma# be transferred naturall# from'. aeruginosa to a different species of bacterium.

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[Total '5 marks!



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2. The outer surface of a plasma (cell surface) membrane incorporates gl#coproteins ofman# different t#pes.

?n some t#pes of cell$ some of these gl#coproteins ha/e a carboh#drate component

that is a pol#saccharide. This consists of a long unbranched chain of repeating sugarunits$ as shown in &ig. '.

The pol#saccharide component extends into the tissue fluid surrounding the cells andin some tissues links the cells together$ forming part of the mechanical support for thetissue.

&ig. ' also shows the chemical structure of one of the component sugar units of thepol#saccharide.

s u g a r u n i t s

p r o t e i n

l o n g u n b r a n c h e d p o l # s a c c h a r i d e

o n e s u g a r u n i t

codes for a protein which regulates transcription. "xpression of allele >allows stimulation of mitosis in the buds which become tillers.

Allele thas a HstopJ triplet within its DBA seuence as well as at its end.

(i) 3tate what is meant b# a HstopJ triplet.

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(ii) Describe the effect of the HstopJ triplet withinthe DBA seuence of allele t.

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(iii) 3uggest how the protein encoded b# allele >ma# regulate transcription.

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(d) The number of tillers per plant and the number of times each tiller branched wererecorded for wild t#pe >>plants and for ttplants which had been gi/en a cop# ofallele >b# genetic engineering.

The results are shown below.

22

' 2

2

0 2

' 0 5

k e # : w i l d t # p e p l a n t s> >

g e n e t i c a l l # m o d i f i e d

t t S > p l a n t s

n u m b e r o f

t i l l e r s

p e r p l a n t

n u m b e r o f b r a n c h e s p e r t i l l e r

(i) With reference to the figure abo/e$ compare the effect of the two ricegenot#pes on tiller growth.

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Macmillan Academy 4


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(ii) 3uggest wh# the expression of allele >ma# be changed when it istransferred b# genetic engineering into rice plants with the genot#pe tt.

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[Total '5 marks!

33. ?n this uestion$ one mark is a/ailable for the ualit# of spelling$ punctuation andgrammar.

ompare selecti/e breeding with the e/olutionar# process.

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[Total 6 marks!

3#. eler# plants produce chemical signals when attacked b# herbi/orous insects. Thesignals switch on the plantsJ resistance genes that code for insecticides.

(i) 3uggest wh# celer# produces its insecticides onl# when attacked b# insects.

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(ii) %utline the steps b# which resistance to an insecticide ma# arise and spread inan insect population.

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[Total 1 marks!

3$. (a) ats with either black or white fur are common in @ritainN brown fur is rarer. Thedominant allele$ -$ of one gene gi/es black fur and the recessi/e allele$ b$ brownfur.

;an# of the white cats carr# a dominant allele$ *$ of a second gene which inhibitspigment production no matter which pigment-producing alleles are present in thegenot#pe. The recessi/e allele$ * has no effect on fur colour.

+enes *and-bare not linked and neither is on the R chromosome.

(i) 3tate the fur colour of cats with the following genot#pes:

*-- ...................................................................................................

-- ....................................................................................................

*bb .....................................................................................................

bb ......................................................................................................

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(ii) 3tate the name gi/en to this t#pe of gene interaction.

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(iii) 3uggest how one gene ma# inhibit the action of another.

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(b) Two white cats produced a litter of kittens with three different coat colours: white$black and brown.

(i) 3tate onepossible genot#pe for echof the two white parents and explainthe reasons for #our choice.

ou ma# use the space below for rough work$ if needed.

genot#pes of parents ............................................................................

explanation ............................................................................................

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(ii) 3tate the ratio of phenot#pes this pair of cats would be expected to producein time$ when the fur colour of se/eral litters of kittens could be recorded.

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[Total '5 marks!

36. "stimates of heritabilit# for /arious phenot#pic traits in Wag#u cattle are shown in thetable below.

phenot#pic trait heritabilit#

* HmarblingJ of meat with fat 2.6

- growth rate 2.0C

C thickness of subcutaneous fat 2.'5

area of Hrib e#eJ meat 2.2

3tate which of the Wag#u phenot#pic traits shown in Table 0.' could most easil# beimpro/ed b# selecti/e breeding. "xplain #our answer.

phenot#pic trait ........................................................................................................

explanation ..............................................................................................................

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[Total 0 marks!



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37. A number of different crop plants ha/e been geneticall# engineered to express a genefor an insecticidal toxin (+t toxin) from a bacterium$ +acillus thuringiensis$ that killsman# insect species.

?n hina$ +t cotton has been grown since '661. A sur/e# at the end of 22' showedthat it was being grown b# o/er two million farmers on fields totalling more than

1222km.

3ome further findings of the sur/e# are shown in the table below.

sur/e# findingpercentage of reported cases

of insecticide poisoningamong cotton farmers

cost of producing 'kgof cotton E 3 U

farmers growing non-+t cotton .0

farmers growing +t cotton 5 '.,'

omment on the findings of the sur/e#.

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3. The lea/es of tomato plants are usuall# dark green. A /ariet# known as H3unn#J has#ellow-green lea/es when grown under the same conditions as dark green /arieties.

A H3unn#J plant was allowed to self-pollinate and man# seeds were collected from its

fruit. A class of students germinated some of these seeds in pots$ each containingC2 g of compost and 52 cm

0of water. 3ix seeds were planted in each pot. The pots

were placed in an incubator at , V for four da#s and then on a bench near a windowin bright da#light for a further four da#s$ after which the seedlings were examined andthe colour of their lea/es recorded.

3ome of the studentsJ results are shown in Table '.

>b+e 1

pot numbers of seedings de/eloped after C da#sdark green #ellow-green #ellow

* 0 2

- 2 , 2

C ' '

' 2

0 '

0 ' '

After all the data had been recorded$ totals were calculated and are shown in Table .

>b+e 2

numbers of seedings de/eloped after C da#s

dark green #ellow-green #ellow

totals C 5, 00

ratio

(a) alculate the ratio of dark green ? #ellow-green ? #ellow seedlings to the nearestwhole number and enter this ratio in the spaces pro/ided in Table .

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(b) "xplain the results shown in Table .

ou ma# include a genetic diagram as part of #our explanation. "xplain an#s#mbols that #ou use.

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(c) The student who had been responsible for pot - was concerned that there mustha/e been some error because all six of the seedlings were the same.

Another student said that the totals of the results$ shown in Table $ seemed soHgoodJ that the# must ha/e been HfiddledJ$ i.e. must ha/e been a scientific fraud.

omment on the /iews of these two students.

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(d) The seedlings were left to grow in the pots for a further ' da#s. The potsremained in bright light and were watered regularl#.

8 All the #ellow seedlings died.

8 The dark green seedlings grew larger than the #ellow-green seedlings.

"xplain these obser/ations.

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[Total ' marks!

3. ?n guinea pigs$ the genes for coat texture and coat colour are found on separatechromosomes. The allele for rough coat is dominant to the allele for smooth coat. Theallele for black coat is dominant to the allele for white coat.

A black guinea pig with a rough coat was crossed with a white guinea pig with a roughcoat.

The cross was repeated on a number of occasions and the phenot#pes of the offspringwere as follows:

C rough and black coats

0' rough and white coats

'' smooth and black coats

'2 smooth and white coats



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omplete the genetic diagram to explain this cross.

se the following s#mbols to represent the alleles:

& = rou)h r = smooth

- = b+ck b = white

*arental phenot#pes: rough and black coat K rough and white coat

*arental genot#pes: ................................. ..................................

+ametes: ................................. ..................................

%ffspring genot#pes: ...............................................................................................

%ffspring phenot#pes: .............................................................................................

"xpected phenot#pic ratio: ......................................................................................[Total 5 marks!



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#. A gene controlling coat colour in cats is sex +inked. The two alleles of this gene areblack and orange. When both the black and orange alleles are present$ the coat colourproduced is called tortoiseshell.

(i) Define the following terms.

gene ................................................................................................................

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allele ...............................................................................................................

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(ii) "xplain wh# there are no male tortoiseshell cats.

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[Total 5 marks!

Macmillan Academy 5


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#1. 7esistance to the poison warfarin is now extremel# common in rats. Warfarin inhibitsan en9#me in the li/er that is necessar# for the rec#cling of /itamin . This /itamin isin/ol/ed in the production of substances reuired for blood clotting. There are two

alleles of the gene that code for this en9#me. 7esistant rats ha/e the allele &&N rats

susceptible to warfarin ha/e the genot#pe &4&

4.

8 7ats susceptible to warfarin die of internal bleeding.

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(b) (i) 3tate how the allele for warfarin resistance originated.

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(ii) "xplain how the allele spread through the population.

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(c) 3tate wh# this is an example of ntur+ selection.

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(d) "xplain what is likel# to happen to the freuencies of the two alleles (&&and &

4)

within the rat population o/er a period of time if warfarin use is discontinued.

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[Total ' marks!

#2. (a) The colour of the spines on the stems of raspberr# plants are controlled b# twogenes$ *E and -Eb. The genes are on different pairs of chromosomes.

Allele * produces a pink anthoc#anin pigment in the spines. Allele - has noeffect b# itself$ but increases the colour produced b# allele * to gi/e red spines.Alleles and b ha/e no effect on spine colour. ?n the absence of anthoc#anin$the spines are green.

(i) 3tate the colour of the spines of raspberr# plants with the followinggenot#pes:

*bb ......................................................................................................

-- ......................................................................................................

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(ii) 3uggest how allele - ma# alter the expression of allele *.

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(b) *lants with the genot#pes *-b and bb were cross-pollinated. The resultingseeds were sown and the seedlings grown until their stems de/eloped spines.

(i) Draw a genetic diagram of this cross to show:

8 the phenot#pes of the parents

8 the gametes

8 the genot#pes and phenot#pes of the offspring

8 the ratio of different phenot#pes expected in the offspring.

ratio of phenot#pes of offspring .............................................................

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(ii) "xplain what differences in the phenot#pic ratio would be expected if genes*E and -Eb were on the same homologous pair of chromosomes$ asshown in the figure below.

* -

, b

, b

, b

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[Total '5 marks!

#3. (i) %utline how resistance to an insecticide (pesticide) can arise and spread in a

population of mosuitoes.

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(ii) "xplain briefl# wh# efforts to control the spread of malaria are hindered b# suchinsecticide resistance.

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[Total 5 marks!

5 1 2 meiosis and variation (1)

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