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CO 03. Extension to Mendel: complexities in relating genotype to phenotype. Extension to Mendel. Single-gene inheritance : deviation from complete dominance and recessiveness. Multiple alleles One gene determine more than one trait 2. Multifactorial inheritance. Extension to Mendel.

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co 03
CO 03

Extension to Mendel: complexities in relating genotype

to phenotype

slide2

Extension to Mendel

Single-gene inheritance :

deviation from complete dominance and recessiveness.

Multiple alleles

One gene determine more than one trait

2. Multifactorial inheritance

slide3

Extension to Mendel

Single-gene inheritance :

deviation from complete dominance and recessiveness.

Multiple alleles

One gene determine more than one trait

2. Multifactorial inheritance

fig 3 2
Fig. 3.2

Different dominant relationship

fig 3 3
Fig. 3.3

Pink flower are the

result of imcomplete

dominance

fig 3 4
Fig. 3.4

In codominance, F1 hybrid display the traits of both

parents

dotted

spotted

slide8

Extension to Mendel

Single-gene inheritance :

deviation from complete dominance and recessiveness.

Multiple alleles

Recessive lethal allele

One gene determine more than one trait

2. Multifactorial inheritance

fig 3 5
Fig. 3.5

ABO blood type are

determined by three

alleles of one gene

fig 3 6
Fig. 3.6

How to establish the

dominance relations

between multiple alleles

slide11

Mutations are the source of new alleles

Wild-type allele: frequency more than 1%

Mutant allele: frequency less than 1%

black/yellow

black

Monomorphic

(One wild-type allele)

agouti

ABO blood type: polymorphic

slide13

Extension to Mendel

Single-gene inheritance :

deviation from complete dominance and recessiveness.

Multiple alleles

Recessive lethal allele

One gene determine more than one trait

2. Multifactorial inheritance

slide14

Two alleles with recessive lethal

Some alleles may

cause lethality

slide16

Extension to Mendel

Single-gene inheritance :

deviation from complete dominance and recessiveness.

Multiple alleles

Recessive lethal allele

One gene determine more than one trait

A single gene determines a number of distinct and seemingly

unrelated characteristics is known as pleiotropy.

slide17

Pleiotropy

Sickle-cell anemia

Mutant -globin aggregates to form long-fiber

slide18

Pleiotropy of sickle-cell anemia: dominance relation vary

Cells break down

Oxygen drops

Cells break down before malarial has a chance to reproduce

slide19

Extension to Mendel

Single-gene inheritance :

deviation from complete dominance and recessiveness.

Multiple alleles

One gene determine more than one trait

Multifactorial inheritance

Two genes can interact to determine one trait

Heterogeneous trait

The same genotype does not always produce the same phenotype

slide20

Extension to Mendel

Single-gene inheritance :

deviation from complete dominance and recessiveness.

Multiple alleles

One gene determine more than one trait

Multifactorial inheritance

Two genes can interact to determine one trait

Heterogeneous trait

The same genotype does not always produce the same phenotype

fig 3 11
Fig. 3.11

How two genes interact to produce novel phenotypes

F2 self cross

9:3:3:1, four distinct phenotypes, dihybrid cross of two independent assortment genes

fig 3 12
Fig. 3.12

Complementary gene action

One dominant allele of each of two genes is necessary to produce

the phenotypes.

fig 3 13
Fig. 3.13

Epistatic: the effect of one gene hides the effect of the other gene

Addition of A or B sugars

Recessive epistasis

H allele is epistatic to the I gene

fig 3 14
Fig. 3.14

Dominant epistasis

A produce particular color, but B dominant allele epistatic to A

table 3 2
Table 3.2

Four classes of genotypes produce a variety of phenotypic ratios

fig 3 15
Fig. 3.15

Genetic Heterogeneity

slide28

Heterogeneous trait

A mutation at any one of a number of genes can give

rise to the same phenotype

fig 3 18
Fig. 3.18

Pedigree

analyses

slide30

Extension to Mendel

Single-gene inheritance :

deviation from complete dominance and recessiveness.

Multiple alleles

One gene determine more than one trait

Multifactorial inheritance

Two genes can interact to determine one trait

Heterogeneous trait

The same genotype does not always produce the same phenotype

slide31

The same genotype does not always produce the

same phenotype

Modifier genes

Environment

Penetrance: occurrence in population

Expressivity: seriousness in the individuals

slide32

Modifier genes

Major genes have a large influence, while modifier genes

have a more subtle, secondary effect.

Modifier genes alter the phenotypes produced by the allele

of other genes.

Example: tail length of mouse

T allele: 10%, 50%, 75% of the normal tail-length

fig 3 19
Fig. 3.19

The Environment can affect the phenotypic expression

Permissive temp.

Restrictive temp.

slide35

The more genes or alleles, the more possible phenotypic

classes, and the greater the similarity to continuous variation

fig 3 9
Fig. 3.9

Some alleles may

cause lethality

fig 3 17
Fig. 3.17

Breeding studies help decide how a trait is inherited

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