ch11 lecture(observable patterns of inheritance)

Observable Patterns of Observable Patterns of InheritanceInheritance

Chapter 11Chapter 11

Earlobe Variation Earlobe Variation

Whether a person has attached or Whether a person has attached or detached earlobes depends on a single detached earlobes depends on a single genegene

Attached earlobes: two copies of the Attached earlobes: two copies of the recessive allele for this generecessive allele for this gene

Detached earlobes: either one or two Detached earlobes: either one or two copies of the dominant allelecopies of the dominant allele

Early Ideas about Heredity Early Ideas about Heredity

People knew that sperm and eggs People knew that sperm and eggs transmitted information about traitstransmitted information about traits

Blending theoryBlending theory Problem:Problem:

Would expect variation to disappearWould expect variation to disappear Variation in traits persistsVariation in traits persists

Gregor MendelGregor Mendel

Strong background Strong background in plant breeding and in plant breeding and mathematicsmathematics

Using pea plants, Using pea plants, found indirect but found indirect but observable evidence observable evidence of how parents of how parents transmit genes to transmit genes to offspringoffspring

GenesGenes

Units of information about specific traitsUnits of information about specific traits

Passed from parents to offspringPassed from parents to offspring

Each has a specific location (locus) on a Each has a specific location (locus) on a chromosomechromosome

AllelesAlleles

Different molecular forms of a gene Different molecular forms of a gene

Arise by mutationArise by mutation

Dominant allele masks a recessive Dominant allele masks a recessive

allele that is paired with itallele that is paired with it

Allele CombinationsAllele Combinations

Homozygous Homozygous having two identical alleles at a locushaving two identical alleles at a locus AAAA or or aaaa

Heterozygous Heterozygous having two different alleles at a locushaving two different alleles at a locus AaAa

Genetic TermsGenetic Terms

A pair of homologous chromosomes

A gene locus

A pair of alleles

Three pairs of genes

Figure 11.4Page 179

Figure 11.4Page 179

Question 1Question 1

1.1. An early idea about inheritance was the An early idea about inheritance was the “blending theory”. What was it and why “blending theory”. What was it and why was it deficient?was it deficient?

Answer 1Answer 1

1.1. An early idea about inheritance was the An early idea about inheritance was the “blending theory”. What was it and why “blending theory”. What was it and why was it deficient?was it deficient?

Traits from the male and female were Traits from the male and female were blended in the offspring.blended in the offspring.

If this were truth, then eventually, all If this were truth, then eventually, all individuality would disappear.individuality would disappear.

Question 2Question 2

2. What does the term “locus” mean?2. What does the term “locus” mean?

Answer 2Answer 2

2. What does the term “locus” mean?2. What does the term “locus” mean?

This is the location of a gene (which This is the location of a gene (which chromosome and where on the chromosome and where on the chromosome). Its “address”.chromosome). Its “address”.

Question 3Question 3

3. What are alleles?3. What are alleles?

Answer 3Answer 3

3. What are alleles?3. What are alleles?

These different molecular forms of the These different molecular forms of the same gene.same gene.

Question 4Question 4

4. If two genes are “homologous”, what 4. If two genes are “homologous”, what does that mean?does that mean?

Answer 4Answer 4

4. If two genes are “homologous”, what 4. If two genes are “homologous”, what does that mean?does that mean?

Homologous means “the same.” They are Homologous means “the same.” They are identical.identical.

Question 5Question 5

5. What does “heterozygous” mean?5. What does “heterozygous” mean?

Answer 5Answer 5

5. What does “heterozygous” mean?5. What does “heterozygous” mean?

Heterozygous means" different”. Heterozygous means" different”. Heterozygous for attached earlobes would Heterozygous for attached earlobes would mean that the individual carries a normal mean that the individual carries a normal gene and a mutant gene.gene and a mutant gene.

Question 6Question 6

6. If Sally is homozygous dominate for 6. If Sally is homozygous dominate for gene A, how would you write that in gene A, how would you write that in standard symbolic form? If she were standard symbolic form? If she were heterozygous for A? If she were heterozygous for A? If she were homozygous for the recessive form of A?homozygous for the recessive form of A?

Answer 6Answer 6

6. If Sally were 6. If Sally were (a)(a) homozygous dominate homozygous dominate for gene A, how would you write that in for gene A, how would you write that in standard symbolic form? standard symbolic form? (b)(b) If she were If she were heterozygous for A? heterozygous for A? (c)(c) If she were If she were homozygous for the recessive form of A?homozygous for the recessive form of A?

AA, Aa, aaAA, Aa, aa

Genotype & PhenotypeGenotype & Phenotype

Genotype refers to particular genes an Genotype refers to particular genes an individual carriesindividual carries

Phenotype refers to an individual’s Phenotype refers to an individual’s observable traitsobservable traits

Cannot always determine genotype by Cannot always determine genotype by observing phenotypeobserving phenotype

Tracking GenerationsTracking Generations

Parental generation Parental generation PP

mates to produce mates to produce

First-generation offspring First-generation offspring FF11

mate to produce mate to produce

Second-generation offspring Second-generation offspring FF22

Monohybrid CrossesMonohybrid Crosses

Experimental intercross between Experimental intercross between

two two FF11 heterozygotes heterozygotes

AA X aa Aa (F1 monohybrids)

Aa X Aa ?

Question 7Question 7

7. Define phenotype.7. Define phenotype.

Answer 7Answer 7

7. Define phenotype.7. Define phenotype.

Phenotype refers to an individual’s Phenotype refers to an individual’s observable traitsobservable traits

Question 8Question 8

8. Define genotype.8. Define genotype.

Answer 8Answer 8

8. Define genotype.8. Define genotype.

Genotype refers to particular genes an Genotype refers to particular genes an individual carriesindividual carries

Question 9Question 9

9. How do you represent the first 9. How do you represent the first generation of a cross?generation of a cross?

Answer 9Answer 9

9. How do you represent the first 9. How do you represent the first generation of a cross? Parental cross? generation of a cross? Parental cross? Second generation?Second generation?

FF11; P; F; P; F22

Question 10Question 10

10. What is monohybrid cross (how many 10. What is monohybrid cross (how many traits are being investigated)?traits are being investigated)?

Answer 10Answer 10

10. What is monohybrid cross (how many 10. What is monohybrid cross (how many traits are being investigated)?traits are being investigated)?

It is a cross where two true breeding It is a cross where two true breeding individuals are mated (individuals are mated (AA x aaAA x aa). Usually ). Usually they are homozygous dominant and they are homozygous dominant and homozygous recessive. One trait (two homozygous recessive. One trait (two alleles).alleles).

Mendel’s Mendel’s Monohybrid Monohybrid

Cross ResultsCross Results

787 tall 277 dwarf

651 long stem

207 at tip

705 purple 224 white

152 yellow428 green

299 wrinkled882 inflated

6,022 yellow 2,001 green

5,474 round 1,850 wrinkled

F2 plants showed dominant-to-recessive ratio that averaged 3:1

Figure 11.5Page 180

ProbabilityProbability

The chance that each outcome of a given The chance that each outcome of a given event will occur is proportional to the event will occur is proportional to the number of ways that event can be reachednumber of ways that event can be reached

Monohybrid Monohybrid CrossCross

IllustratedIllustrated

True-breedinghomozygous recessiveparent plant

True-breedinghomozygous dominantparent plant

An F1 plantself-fertilizesand producesgametes:

F1 PHENOTYPES

F2 PHENOTYPES

aa

Aa

AA

aaAa

Aa

Aa Aa

Aa Aa

Aa Aa

Aa Aa

Aa

Aa

AA

aa

A

A

A

A

a a

a

a

AA

Figure 11.7Page 181

Mendel’s Theory Mendel’s Theory of Segregationof Segregation

An individual inherits a unit of information An individual inherits a unit of information (allele) about a trait from each parent(allele) about a trait from each parent

During gamete formation, the alleles During gamete formation, the alleles segregate from each other segregate from each other

Test CrossTest Cross

Individual that shows dominant phenotype Individual that shows dominant phenotype is crossed with individual with recessive is crossed with individual with recessive phenotypephenotype

Examining offspring allows you to Examining offspring allows you to determine the genotype of the dominant determine the genotype of the dominant individualindividual

Punnett Squares of Punnett Squares of Test CrossesTest Crosses

Homozygous recessive

a a

A

a aa

Aa Aa

aa

Homozygous recessive

a a

A

A Aa

Aa Aa

Aa

Two phenotypes All dominant phenotype

Dihybrid Cross Dihybrid Cross

Experimental cross between individuals Experimental cross between individuals that are homozygous for different that are homozygous for different

versions of versions of twotwo traits traits

Dihybrid Cross: Dihybrid Cross: FF11 Results Results

AABB aabbx

AaBb

AB AB ab ab

TRUE-BREEDING PARENTS:

GAMETES:

F1 HYBRID OFFSPRING:

purple flowers, tall

white flowers,dwarf

All purple-flowered, tall

Figure 11.9 (1)Page 183

1/16aaBB

1/16aaBb

1/16aaBb

1/16Aabb

1/16Aabb

1/16AAbb

1/16AABB

1/16AABb

1/16AaBB

1/16AaBb

1/16AABb

1/16AaBb

1/16AaBB

1/16AaBb

1/16AaBb

1/4 AB 1/4 Ab 1/4 aB 1/4 ab

1/16aabb

1/4 AB

1/4 Ab

1/4 aB

1/4 ab

AaBb AaBbX

1/16 white-flowered, dwarf

3/16 white-flowered, tall

3/16 purple-flowered, dwarf

9/16 purple-flowered, tall

Dihybrid Cross: Dihybrid Cross: FF22 Results Results

Figure 11.9(2)Page 183

Question 11Question 11

11. Describe or define: dihybrid cross”.11. Describe or define: dihybrid cross”.

11. Describe or define: dihybrid cross”.11. Describe or define: dihybrid cross”.

Experimental cross between individuals Experimental cross between individuals that are homozygous for different that are homozygous for different versions of versions of twotwo traits traits

Example:Example:

AABB x aabbAABB x aabb

Independent AssortmentIndependent Assortment

Mendel concluded that the two “units” for Mendel concluded that the two “units” for the first trait were to be assorted into the first trait were to be assorted into gametes independently of the two “units” gametes independently of the two “units” for the other traitfor the other trait

Members of each pair of homologous Members of each pair of homologous chromosomes are sorted into gametes at chromosomes are sorted into gametes at random during meiosis random during meiosis

Independent AssortmentIndependent Assortment

Metaphase I:

Metaphase II:

Gametes:

1/4 AB 1/4 ab 1/4 Ab 1/4 aB

A A A A

A A A A

AAAA

B B

B B

BB

B B

BBBB

a a a a

aa aa

aaaa

bb b b

bb b b

b b b b

OR

Tremendous VariationTremendous Variation

Number of genotypes possible in Number of genotypes possible in

offspring as a result of independent offspring as a result of independent

assortment and hybrid crossing is assortment and hybrid crossing is

22nn

((nn is the number of gene loci is the number of gene loci

at which the parents differ)at which the parents differ)

Impact of Mendel’s WorkImpact of Mendel’s Work

Mendel presented his results in 1865Mendel presented his results in 1865

Paper received little noticePaper received little notice

Mendel discontinued his experiments in Mendel discontinued his experiments in 18711871

Paper rediscovered in 1900 Paper rediscovered in 1900

Dominance Relations Dominance Relations

Complete dominance Complete dominance

Incomplete dominanceIncomplete dominance

CodominanceCodominance

Incomplete Incomplete DominanceDominance

XHomozygous parent

Homozygous parent

All F1 are heterozygous

X

F2 shows three phenotypes in 1:2:1 ratio

Incomplete Dominance

Figure 11.10Page 184

Codominance: ABO Blood Codominance: ABO Blood Types Types

Gene that controls ABO type codes for Gene that controls ABO type codes for enzyme that dictates structure of a enzyme that dictates structure of a glycolipid on blood cellsglycolipid on blood cells

Two alleles (Two alleles (IIAA and and IIBB) are codominant ) are codominant when pairedwhen paired

Third allele (Third allele (ii) is recessive to others) is recessive to others

ABO Blood Type:ABO Blood Type:Allele CombinationsAllele Combinations

Range of genotypes:

Blood types:

IA IA

IA i IA IB IB i

IB IB

ii

A AB B O

or or

Figure 11.11Page 184

ABO and TransfusionsABO and Transfusions

Recipient’s immune system will attack Recipient’s immune system will attack

blood cells that have an unfamiliar blood cells that have an unfamiliar

glycolipid on surfaceglycolipid on surface

Type O is universal donor because it has Type O is universal donor because it has

neither type A nor type B glycolipidneither type A nor type B glycolipid

Question 12.Question 12.

12. What three types of dominance?12. What three types of dominance?

Question 12. What three types of Question 12. What three types of dominance?dominance?

12. What three types of dominance?12. What three types of dominance?

Complete dominance Complete dominance

Incomplete dominanceIncomplete dominance

CodominanceCodominance

Pleiotropy Pleiotropy

Alleles at a single locus may have effects Alleles at a single locus may have effects on two or more traitson two or more traits

Marfan syndrome - Mutation in gene for Marfan syndrome - Mutation in gene for fibrillin affects skeleton, cardiovascular fibrillin affects skeleton, cardiovascular system, lungs, eyes, and skin system, lungs, eyes, and skin

Marfan SyndromeMarfan Syndrome

Epistasis Epistasis

Interaction between the products of gene Interaction between the products of gene pairspairs

Common among genes for hair color in Common among genes for hair color in mammalsmammals

Coat Color Coat Color inin

RetrieversRetrieversbbeeBBEE X

F1 puppies are all BbEe

BBEE

BBEe

BbEE

BbEe Bbee

BbEe

Bbee

BBEe BbEE BbEe

BBee BbEe

bbeebbEe

bbEE bbEe

BE Be bE be

BE

Be

bE

be

black

brown

yellow

F2 puppies

Figure 11.13Page 186

Comb Shape in PoultryComb Shape in Poultry

9/16 walnut 3/16 rose 3/16 pea 1/16 singlerrpp

RRpp(rose comb)

rrPP(pea comb)

RrPp (all walnut comb)

P:

F2:

F1:

X

RRPPRRPpRrPPRrPp

RRppRrpp

rrPPrrPp

Figure 11.15Page 187

Walnut CombWalnut Comb

http://www.longtail-fowl.com/images/sketches/minohiki_headstudy_1.jpg

Campodactyly: Campodactyly: Unexpected Phenotypes Unexpected Phenotypes

Effect of allele varies:Effect of allele varies:

Bent fingers on both handsBent fingers on both hands

Bent fingers on one handBent fingers on one hand

No effectNo effect

Many factors affect gene expressionMany factors affect gene expression

Continuous VariationContinuous Variation

A more or less continuous range of small A more or less continuous range of small differences in a given trait among differences in a given trait among individualsindividuals

The greater the number of genes and The greater the number of genes and

environmental factors that affect a trait, the environmental factors that affect a trait, the

more continuous the variation in versions more continuous the variation in versions

of that traitof that trait

Human VariationHuman Variation

Some human traits occur as a few discrete Some human traits occur as a few discrete typestypes Attached or detached earlobes Attached or detached earlobes Many genetic disordersMany genetic disorders

Other traits show continuous variationOther traits show continuous variation HeightHeight WeightWeight Eye colorEye color

Describing Continuous Variation Describing Continuous Variation

Range of values for the trait

Nu

mb

er o

f in

div

idu

als

wit

hso

me

valu

e o

f th

e t

rait

(line of bell-shaped curve indicates continuous variation in population)

Range of values for the trait

Nu

mb

er o

f in

div

idu

als

wit

hso

me

valu

e o

f th

e t

rait

Question 13.Question 13.

13. Define pleiotrophy.13. Define pleiotrophy.

Question 13Question 13

13. Define pleiotrophy.13. Define pleiotrophy.

Alleles at a single locus may have Alleles at a single locus may have effects on two or more traitseffects on two or more traits

Examples: Marfan’s syndrome and Examples: Marfan’s syndrome and Sickle Cell AnemiaSickle Cell Anemia

Temperature Effects Temperature Effects on Phenotype on Phenotype

Rabbit is homozygous for Rabbit is homozygous for an allele that specifies a an allele that specifies a heat-sensitive version of an heat-sensitive version of an enzyme in melanin-enzyme in melanin-producing pathwayproducing pathway

Melanin is produced in Melanin is produced in cooler areas of bodycooler areas of body

Figure 11.18Page 190

Environmental Effects on Plant Environmental Effects on Plant PhenotypePhenotype

Hydrangea macrophyllaHydrangea macrophylla

Action of gene responsible for floral Action of gene responsible for floral color is influenced by soil aciditycolor is influenced by soil acidity

Flower color ranges from pink to blueFlower color ranges from pink to blue