Mendel and the Gene Idea

Page
13

Slide 93

Fig. 14-UN2

Degree of dominance

Complete dominance

of one allele

Incomplete dominance

of either allele

Codominance

Description

Heterozygous phenotype

same as that of homo-

zygous dominant

Heterozygous phenotype

intermediate between

the two homozygous

phenotypes

Heterozygotes: Both

phenotypes expressed

Multiple alleles

Pleiotropy

In the whole population,

some genes have more

than two alleles

One gene is able to

affect multiple

phenotypic characters

CRCR

CRCW

CWCW

IAIB

IA , IB , i

ABO blood group alleles

Sickle-cell disease

PP

Pp

Example

Slide 94

Fig. 14-UN3

Description

Relationship among

genes

Epistasis

One gene affects

the expression of

another

Example

Polygenic

inheritance

A single phenotypic

character is

affected by

two or more genes

BbCc

BbCc

BC

BC

bC

bC

Bc

Bc

bc

bc

9

: 3

: 4

AaBbCc

AaBbCc

Slide 95

Fig. 14-UN4

Slide 96

Fig. 14-UN5

George

Sandra

Tom

Sam

Arlene

Wilma

Ann

Michael

Carla

Daniel

Alan

Tina

Christopher

Slide 97

Fig. 14-UN6

Slide 98

Fig. 14-UN7

Slide 99

Fig. 14-UN8

Slide 100

Fig. 14-UN9

Slide 101

Fig. 14-UN10

Slide 102

Fig. 14-UN11

Slide 103

You should now be able to:

Define the following terms: true breeding, hybridization, monohybrid cross, P generation, F1 generation, F2 generation

Distinguish between the following pairs of terms: dominant and recessive; heterozygous and homozygous; genotype and phenotype

Use a Punnett square to predict the results of a cross and to state the phenotypic and genotypic ratios of the F2 generation

Slide 104

Explain how phenotypic expression in the heterozygote differs with complete dominance, incomplete dominance, and codominance