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1. The diagram below represents stages in the production of human sperm.

(a) Name the type of cell division that produces sex cells.

(b) State the number of chromosomes which would be present in the cells labelledA, Band C.

A: _ B: C: _

(c) Compare the appearance of the chromosomes in cell B and cell C.

(d) Name the two processes which increase variation during the 1st division of thesperm mother cell.

1

2 _

(e) State the location of sperm production in the testes.

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2. Some stages in the process of meiosis are shown in the diagrams below.

Only 6 chromosomes are shown in each cell.

A B Dc

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(a) (i) Place the stages in the correct order.

(ii) At which stage could chiasmata form?

(iii) Why are chiasmata important?

(b) The diagram below shows a gamete mother cell and four sperm which wouldresult from meiosis.

(i) Complete the diagram by writing in the normal number ofchromosomes found in each of the cells. 1

Gamete mother cellSperm

(ii) In how many of these sperm will an X chromosome be found?

(iii) Where in the testes does meiosis occur?

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3. The graph below shows the mass of DNA present as gamete mother cells developinto sperm cells during meoisis in the testes. P and Q represent cells atintermediate stages in this process.

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Mass ofDNA(arbitrary 2

units)

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Gametemother cells

Q Sperm cellsp

(a) Explain why the mass of DNA changes between

(i) the gamete mother cells and cell type P _

(ii) cell types P and Q. _

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3. (continued)

(b) The diagram below shows a pair of chromosomes in a cell undergoing meiosis.

cross-overpoint

Letters Rand T represent dominant alleles of two different genes.

(i) What name is given to the point on the chromosomes where crossmgover occurs?

(ii) Assuming that crossing over does occur, give all the combinations ofalleles that would be present in the resulting gametes.

(iii) Crossing over leads to genetic variation.

Name one other way in which meiosis increases variation.

(c) State the exact location of meiosis in the testes.

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4. The family tree below shows the inheritance of a genetic disorder.

Key to symbols

o male

o female

• affected maleJack Gill

tit affected female

Tony Mary

(a) State whether the disorder is dominant or recessive and give a reason for youranswer.

Dominant/recessive

Reason __

(b) Using symbols Band b to represent the alleles, give the genotypes of Tonyand Mary.

Tony Mary

(c) Jack.and Gill are expecting a third child.What is the percentage chance of this child inheriting the disorder?

_______________ 0/0

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5. Thalassaemia is an inherited blood disorder in which haemoglobin is affected. MarksThe condition illustrates incomplete dominance in which the recessive allele has apartial effect. Heterozygous individuals show mild symptoms.

The diagram below shows the incidence of thalassaemia in three generations of afamily.

~ male with mild thalassaemia

@ female with mild thalassaemia

• male with severe thalassaemia

o unaffected female

Philip

Carla

Charles

(a) Using the symbol HbA to represent the allele for normal haemoglobin, andthe symbol HbB to represent the recessive allele, complete the table to showthe genotypes of Anne, Philip and Charles.

Individual Genotype

Anne

Philip

Charles

(b) Mark and Carla have a third child. What is the percentage chance that thechild will have the same genotype as the parents?

Space for calculation

_____ % 1

(c) Haemoglobin is found in red blood cells. Where in the body are red cellsmanufactured and destroyed?

Manufactured Destroyed

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6. The diagram below shows the inheritance of tongue-rolling ability in a family.

o Male tongue-rollero Female tongue-roller

• Male non tongue-roller• Female non tongue-roller

P

(a) (i) Using the symbol R to represent the allele for tongue-rolling, and thesymbol r to represent the allele for non tongue-rolling, state thegenotypes of individuals P and T.

P _ T _

(ii) How many individuals, shown In this family tree, have a genotypewhich is homozygous recessive?

(iii) Place a cross through a symbol in the family tree which represents aheterozygous male. 1

(iv) Female S is pregnant. Using information from the family tree, is itpossible to predict whether the child will be a tongue-roller or not?Give a reason for your answer.

YES/NO

Reason _

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(b) Some characteristics are controlled by several genes.

(i) State the term used to describe this type of inheritance pattern.

(ii) Which two of the following human characteristics show this type ofinheritance pattern? Underline the correct answers.

blood groups cystic fibrosis height

haemophilia skin colour

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7. The Rhesus blood group system is determined by three pairs of alleles: Cc, Ddand Ee. However, only the D allele is important in blood transfusion andpregnancy. People with the dominant allele D are Rhesus positive and those withgenotype dd are Rhesus negative.

(a) What term is used to describe characteristics controlled by many pairs ofalleles?

(b) Name another blood group system which has to be matched for bloodtransfusion to be successful.

(c) What part of a cell carries the Rhesus antigen?

(d) A Rhesus negative woman and a Rhesus positive man are planning to have achild. They consult a genetics counsellor to find out whether their child islikely to be Rhesus positive or Rhesus negative.

What genetic information could they be given?

(e) Describe a treatment which can be used to protect a child at risk from theRhesus reaction.

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8. (a) The MN blood group system is determined by two alleles, M and N. Each ofthese alleles controls the production of a different antigen on the cellmembrane of red blood cells.

M and N are co-dominant.

(i) Two parents, who are heterozygous for this blood group, have a son.Complete the Punnett square below to show the parental gametes andthe possible genotypes of their son.

ParentsGenotype

MotherMN x

FatherMN

mother's gametes

MNfather's gametes

(ii) .The son has a different genotype to either of his parents. What are thechances of this happening?

Space for calculation

% 1------

(ill) Describe how the son's phenotype differs from his parents.

(b) The immune system recognises antigens on the cell membrane as self ornon-self.

What term describes

(i) an immune reaction to self antigens?

(ii) an over-reaction to a normally harmless non-self antigen?

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9. Sickle-cell anaemia is a blood disorder in which haemoglobin is malformed.

The diagram below shows the effect of this disorder on a red blood cell.

Normal red blood cell Sickled red blood cell

The condition is not sex-linked. The allele for normal haemoglobin (H) IS

incompletely dominant to the sickle-cell allele (h).

Heterozygous individuals are mildly affected, whereas those with genotype hh are .severely affected.

Two mildly affected parents have two children who are mildly affected like theirparents. The parents are expecting a third child.

(a) Complete the Punnett square to show the possible genotypes of this child.

(b) From the Punnett square calculate the percentage chance of the child being

1 unaffected

2 mildly affected

3 severely affected.

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Marks10. Three different alleles determine the ABO blood groups. Allele A and allele Bare

both dominant to allele 0.

(a) Alleles A and B are both expressed in heterozygous individuals who haveblood group AB. What term is used to describe the relationship betweenalleles A and B?

(b) (i) A man with blood group AB marries a woman with blood group O.State the genotypes of the parental gametes and use them to completethe Punnett diagram below.

man woman

parental phenotypes AB x ogamete genotypes

Punnett diagram

(ii) State the possible phenotypes of the children and the ratio in whichthey would be expected to occur.

Phenotypes

Ratio

(iii) .Which of the parents would be able to -donate blood safely to any oftheir children? Give a reason for your answer.

Parent

Reason

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11. The blood group of an individual is controlled by three alleles A, B- and O.

Alleles A and B are co-dominant and completely dominant to allele O.

The diagram below shows the blood groups of three generations of a family.

Parents MotherGroup B

FatherGroup A

Children Son 2Group 0

Daughter T HusbandGroup 0

Son 1Group A

Grandchildren GrandsonGroup B

GranddaughterGroup A

(a) What is the blood group of the daughter?

(b) State the genotypes of the grandchildren.

Grandson Granddaughter _

(c) How many of the three children are homozygous?

(d) Explain the meaning of the term co-dominant.

(e) Only one of the sons can safely receive a blood transfusion from his brother.Indicate whether this statement is true or false and explain your decision.

True/False

Explanation .:.._ ---:- _

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Three different alleles determine the ABO blood groups. Allele A and allele Bareboth dominant to allele 0.

(a) Alleles A and B are both expressed in heterozygous individuals who haveblood group AB. What term is used to describe the relationship betweenalleles A and B?

(b) (i) A man with blood group AB marries a woman with blood group O.State the genotypes of the parental gametes and use them to completethe Punnett diagram below.

man woman

parental phenotypes AB x ogamete genotypes

Punnett diagram

(ii) State the possible phenotypes of the children and the ratio in whichthey would be expected to occur.

Phenotypes

Ratio

(iii) Which of the parents would be able to '€lonate blood safely to any oftheir children? Give a reason for your answer.

Parent

Reason

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13.The gene for this blood group has three alleles. Alleles A and Bareco-dominant to allele O.

A man, heterozygous for blood group A, and a woman of blood group AB,have children.

(a) (i) State the genotypes of the parents.

female _ male _

(ii) Complete the Punnett square below to show the genotypes of theirgametes and the genotypes of the children they may have.

(iii) What is the percentage chance that a child of these parents would haveblood group A?

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14. The diagram below shows inheritance of the ABO blood group over threegenerations of a family. The letters represent the blood group of each individual.

DMale

1

6

2 o Female

3 4 5

B

7 8

(a) The ABO blood group system is controlled by three alleles: A, Band O.Alleles A and B are co-dominant and both are completely dominant to allele O.

(i) State the genotypes of the following:

Individual 1 _

Individual 3 _

(ii) What is the blood group of individualS? Give a reason for your answer.

Blood group _

Reason ___

(iii) How many of the individuals shown in the family tree have a genotypewhich is heterozygous?

(b) During an operation, individual 4 needed a blood transfusion.

Identify all the individuals in the family tree who could safely donate blood toher.

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15. Polydactyly is an inherited condition in which individuals are born with extra toes. MarksThe allele for polydactyly is dominant and not sex-linked.The family tree below shows the incidence of the condition through threegenerations.

Grandparents

o unaffected male

o unaffected female

• affected male

• affected female

Parents x y

Children

(a) (i) Using the symbol D for the allele for polydactyly and d for the normalallele, give the genotypes of the two children.

and 1

(ii) Individuals X and Yare expecting another child.

What-are the chances of this child inheriting the condition?

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(b) (i) What evidence from the family tree confirms that th~ grandfather isheterozygous?

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(ii) What evidence from the family tree confirms that the condition is notsex-linked?

(c) What term is used to refer to chromosomes which are not sex-chromosomes?

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16. The family tree shows the inheritance of a bone disorder.

Parents

• Affected female

o Unaffected female

• Affected male

D Unaffected male

p Q R s

The disorder is caused by a dominant sex-linked allele (B).

(a) Using appropriate symbols, give the genotypes of individuals P, Q, Rand S.

P Q R S _

(b) (i) Explain why all the F, females in this family are affected.

(ii) Explain why only some of the F2 females in this family are affected.

(c) Is the ratio of affected offspring to unaffected offspring in the F, generationas expected? Give a reason for your answer.

Yes/No _

Reason __

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17. The diagram below represents the two sex chromosomes.

x y

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(a) Using the letter H, mark on the diagram the likely position of the sex-linkedallele which causes haemophilia. (1)

(b) What term is used to describe the other 44 chromosomes found in a normaldiploid cell?

(c) Describe how a karyotype can be used to detect genetic disorders.

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18. Achondroplasia is an autosomal disorder of bone growth that is caused by a genemutation. A person with this condition has relatively short arms and legs.The incidence of achondroplasia in a family is shown in the diagram below.

Keyo = unaffected female

D= unaffected male

• = affected female

• = affected male

G H J

(a) (i) In this family, the mutation occurred in an ovum.In which individual did the mutation take place?

(ii) Describe a change which takes place in a gene when it mutates.

(b) The allele which causes achondroplasia is dominant.What is the percentage chance that a child of Hand J would inheritachondroplasia?Space for calculation

(c) People who are affected by achondroplasia do not produce enough growthhormone. State the site of growth hormone production.

(d) The list below contains a number of inherited disorders.

Phenylketonuria Down's syndrome Huntington's choreaHaemophilia Cystic fibrosis

Select a disorder from this list which is:

(i) the result of non-disjunction;

(ii) a sex-linked condition.

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19.(a) The diagram below shows the base sequence in part of a DNA strand.

A G G

I I IT TI I

cI

(i) What two amino acids are coded for by this strand of DNA?

______________________ and _

(ii) If the base A was replaced by the base C as a result of a mutation in thestrand above, which two amino acids would result?

______________________ and _" _

(iii) 'What name is given to this type of mutation?

(iv) Why is this type of mutation potentially less harmful than an insertionor deletion mutation?

(b) Name bases A and C.

A _ C __

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What you should know(Chapters 11-14) .

(See table 14.3 for word bank.)

1 A cross is one that involves two parentsrti ularwho differ in one way with respect to a pa c

characteristic.

2 One member of a pair of alleles of a gene exhibitsdominance if it completely ----

theexpression of the other allele in the phenotyperesulting from the heterozygote.

3 The members of a pair of alleles show ----dominance if the heterozygote results in ah type between those of the twop eno

homozygotes.

4 The members of a pair of alleles show ifthe heterozygote produces a phenotype where bothalleles are expressed.

5 If three or more alleles of a gene exist, it is said tohave alleles.

@ What you should know(Chapters 11-14) ____ . Analysis of a family tree relating to a

genetic disorder enables a genetic to.help people make decisions about parenthood basedon assessment of _

14 A is a display of a complement ofchromosomes showing their form, size and number.

15 and chorionic villus sampling enablematerial to be karyotyped and inspected----

for chromosomal abnormalities.

16 Risk evaluation in cases of polygenic inheritance isusually _

17 Post-natal is done to identify babiessuffering phenylketonuria.

6 Human females possess a pair of homologous sexchromosomes called X chromosomes; human maleshave one X and a Y chromosome whichis to part of the X chromosome.

7 Genes present on an X chromosome but not on a Ychromosome are said to be _

8 A characteristic which shows variation iscontrolled by alleles of more than one gene and issaid to show inheritance.

9 Mutations are changes in the whichinvolve an alteration of type or sequence

I in DNA or a change in of chromosomes.

10 Substitution and bring about minorchanges and are called point mutations; insertionand lead to major changes and are calledfrarneshift mutations.

WYSK 11 - 14 Inheritance

abnormalities foetalamniocentesis fullybase geno~eco-dominance homologouscomplete incompletecontinuous intermediatecounsellor inversiondeletion karyotypeempirical Dlasksfamily tree monohybrid

multiplemutagenicnon-disjunctionnumberpolygenicrandomriskscreeningsex-linkedsmaller

11 Mutations occur rarely and at . Theirfrequency can be increased by agents.

.12 occurs when a spindle fibre fails duringmeiosis and the members of a pair of homologouschromosomes fail to separate. This results in somegametes receiving one chromosome too many orone chromosome too few and leads to the formationof individuals suffering chromosomal _

13 A pattern of inheritance amongst the members of afamily can be established by constructing a Table 14.3 Word bank for chapters 11-14

What you should know(Chapters9-10)

(See table 10.3 for word bank.)

1 A is a unit of heredity which controls acharacteristic. It consists of a region of _on a chromosome.

2 A species' chromosome is thecharacteristic number of chromosomes that itpossesses (46 in a human). These can bearranged into pairs which match oneanother gene for gene.

3 In a human, one pair of chromosomes determinesthe of the individual and are called thesex chromosomes. The other 22 pairs are called

4 A cell containing 46 chromosomes as 23 pairs is____ ; a cell containing 23 _chromosomes is haploid.

S is the process by which the nucleus of adiploid gamete mother cell divides htto four, resultingin the formation of four ----

6 Prior to nuclear , the amount ofchromosomal material doubles by DNAundergoing and reproducing itselfexactly.

7 DNA replication allows genetic information to bepassed on from cell to cell and from generation to

8 Meiosis involves two consecutive _divisions and produces gametes inpreparation for sexual reproduction.

9 During meiosis, new combinations of existing allelesarise by independent and _between homologous chromosomes.

10 The meeting of two haploid gametes at fertilisationallows mixing of part of one person's _with that of another. By producing diploid individualswho are genetically different from their parents, thisprocess produces amongst the membersof the human species.

assortment DNA meIOSISautosomes gametes nuclearchromosomes gene replicationcompliment generation sexcrossing over genotype unpaireddiploid haploid variationdivision homologous

Table 10.3 Word bank for chapters 9-10

Essay Questions

1. Describe /low the process of meiosis brings about variation in the humanpopulation, under the following headings:

i) PuTangementofcbromosomes (5)

ii) Exchange of genes (5)

(10)

2. Outline the main mechanism of sex-linked inheritance in humans bvnaming a sex-linked characteristic and showing how it is transmitted {romone generation to the next

(lU)

Maximum 8 marks

1mark coherence

1 mark relevance

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