Mendel and the Gene Idea

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5

Pp

Pp

Pp

Pp

Pp

Pp

pp

pp

TECHNIQUE

Slide 33

Fig. 14-7b

RESULTS

All offspring purple

or

1/2 offspring purple and

1/2 offspring white

Slide 34

The Law of Independent Assortment

Mendel derived the law of segregation by following a single character

The F1 offspring produced in this cross were monohybrids, individuals that are heterozygous for one character

A cross between such heterozygotes is called a monohybrid cross

Slide 35

Mendel identified his second law of inheritance by following two characters at the same time

Crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters

A dihybrid cross, a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independently

Slide 36

Fig. 14-8

EXPERIMENT

RESULTS

P Generation

F1 Generation

Predictions

Gametes

Hypothesis of

dependent

assortment

YYRR

yyrr

YR

yr

YyRr



Hypothesis of

independent

assortment

or

Predicted

offspring of

F2 generation

Sperm

Sperm

YR

YR

yr

yr

Yr

YR

yR

Yr

yR

yr

YR

YYRR

YYRR

YyRr

YyRr

YyRr

YyRr

YyRr

YyRr

YYRr

YYRr

YyRR

YyRR

YYrr

Yyrr

Yyrr

yyRR

yyRr

yyRr

yyrr

yyrr

Phenotypic ratio 3:1

Eggs

Eggs

Phenotypic ratio 9:3:3:1

1/2

1/2

1/2

1/2

1/4

yr

1/4

1/4

1/4

1/4

1/4

1/4

1/4

1/4

3/4

9/16

3/16

3/16

1/16

Phenotypic ratio approximately 9:3:3:1

315

108

101

32

Slide 37

Fig. 14-8a

EXPERIMENT

P Generation

F1 Generation

Predictions

Gametes

Hypothesis of

dependent

assortment

YYRR

yyrr

YR

yr

YyRr



Hypothesis of

independent

assortment

or

Predicted

offspring of

F2 generation

Sperm

Sperm

YR

YR

yr

yr

Yr

YR

yR

Yr

yR

yr

YR

YYRR

YYRR

YyRr

YyRr

YyRr

YyRr

YyRr

YyRr

YYRr

YYRr

YyRR

YyRR

YYrr

Yyrr

Yyrr

yyRR

yyRr

yyRr

yyrr

yyrr

Phenotypic ratio 3:1

Eggs

Eggs

Phenotypic ratio 9:3:3:1

1/2

1/2

1/2

1/2

1/4

yr

1/4

1/4

1/4

1/4

1/4