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Lecture 2 (continue) Modifications to Mendelian Genetics Complexities in relating phenotypes to genotypes. Dominant epistasis. The dominant allele of the first gene block the expression of the second gene regardless of the second gene’s alleles. white AABB x aabb green. F1 AaBb (white).

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slide1

Lecture 2 (continue)

Modifications to Mendelian Genetics

Complexities in relating phenotypes to genotypes

slide2

Dominant epistasis

The dominant allele of the first gene block the expression of the second gene regardless of the second gene’s alleles.

white AABB x aabb green

F1 AaBb (white)

F2 12 (white): 3 (yellow): 1 (green)

9/16 A_B_ white

3/16 aaB_ white

3/16 A_bb yellow

1/16 aabb green

b(enzyme) A(enzyme)

Precusor (white) -----> green pig. -------> yellow pig.

slide3

Dominant epistasis

  • fruit color of summer squash

Difference btw this and monhybrid

F1 looks same with dom/reccesive

F2 is neither 3:1 or 1:2:1 ratio

and also additional new phenotype

(yellow)

slide4

Testcross of F1 with dominant epistasis

Not the expected 1:1 ratio!

AaBb x aabb [white x green]

1/4 AaBb ------- A_B_ ( )

1/4 Aabb -------- A_bb ( )

1/4 aaBb -------- aaB_ ( )

1/4 aabb -------- aabb ( )

b(enzyme) A(enzyme)

Precusor (white) -----> green pig. -------> yellow pig.

slide5

Testing genetic models with chi-square test

Consider the following genetic data collected from the crossing of snapdragons.

Flower colors of snapdragons can be red, pink or white; leaf color can be green or yellow. You get the following numbers of offspring by crossing two pink-flowered, yellow-leaved snapdragons. What genetic models can be applied to explaining the inheritance patterns of flower and leaf colors?

Phenotypes obs. No.

Red flowers, green leaves 10

Pink flowers, green leaves 19

White flowers, green leaves 9

Red flowers, yellow leaves 17

Pink flowers, yellow leaves 28

White flowers, yellow leaves 13

Total 96

Think each trait

Flower color

self-cross of one phenotype

results in three categories of phe.

Candidate model

Incomplete dominance (1:2:1)

vs

Recessive epistasis (9:3:4)

slide6

Testing genetic models with chi-square test

Consider the following genetic data collected from the crossing of snapdragons.

Flower colors of snapdragons can be red, pink or white; leaf color can be green or yellow. You get the following numbers of offspring by crossing two pink-flowered, yellow-leaved snapdragons. What genetic models can be applied to explaining the inheritance patterns of flower and leaf colors?

Phenotypes obs. No.

Red flowers, green leaves 10

Pink flowers, green leaves 19

White flowers, green leaves 9

Red flowers, yellow leaves 17

Pink flowers, yellow leaves 28

White flowers, yellow leaves 13

Total 96

Think each trait

2) Leaf color

Self-cross of one phenotype

results in two categories of phe.

Candidate models

Complete dominance (3:1)

vs

Lethal allele (2:1)

vs

Complementation (9:7)

slide7

Testing genetic models with chi-square test

1) Model 1 (flower incomplete dom; leaf color complete dom)

Phenotypes obs. No. exp ratio (exp No) (O-E)2/E

Red flowers [1/4], green leaves [1/4] 10 1/4 x 1/4= 1/16 ( )

Pink flowers [2/4], green leaves [1/4] 19 2/4 x 1/4= 2/16 ( )

White flowers [1/4], green leaves [1/4] 9 1/4 x 1/4= 1/16 ( )

Red flowers [1/4], yellow leaves [3/4] 17 1/4 x 3/4= 3/16 ( )

Pink flowers [2/4], yellow leaves [3/4] 28 2/4 x 3/4= 6/16 ( )

White flowers [1/4], yellow leaves [3/4] 13 1/4 x 3/4= 3/16 ( )

Total 96 16/16 =1 (96)

df = ? ; 2 = ?

slide8

Testing genetic models with chi-square test

2) Model 2 (flower incomplete dom; leaf color lethal allele)

Phenotypes obs. No. exp ratio (exp No) (O-E)2/E

Red flowers [1/4], green leaves [1/3] 10 1/4 x 1/3= 1/12 ( )

Pink flowers [2/4], green leaves [1/3] 19 2/4 x 1/3= 2/12 ( )

White flowers [1/4], green leaves [1/3] 9 1/4 x 1/3= 1/12 ( )

Red flowers [1/4], yellow leaves [2/3] 17 1/4 x 2/3= 2/12 ( )

Pink flowers [2/4], yellow leaves [2/3] 28 2/4 x 2/3= 4/12 ( )

White flowers [1/4], yellow leaves [2/3] 13 1/4 x 2/3= 2/12 ( )

Total 96 16/16 =1 (96)

df = ? ; 2 = ?

slide9

Testing genetic models with chi-square test

Model 1: df = ? ; 2 = ?

Which one is right?

Model 2: df = ? ; 2 = ?