Genetic problems

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50%: male (one normal, one colorblind)

Slide 25

Question #4B

A couple has a colorblind daughter.

What are the possible genotypes and phenotypes of the parents and the daughter?

Slide 26

Question #4B

Xc Y

XC XCXc XCY

Xc XcXc XcY

parents: XcY and XCXc or XcXc

father colorblind

mother carrier or colorblind

daughter: XcXc - colorblind

Slide 27

Question #5

In humans, the presence of freckles is due to a dominant gene (F) and the non-freckled condition is due to its recessive allele (f).

Dimpled cheeks (D) are dominant to non-dimpled cheeks (d).

Slide 28

Question #5A

Two persons with freckles and dimpled cheeks have two children: one has freckles but no dimples and one has dimples but no freckles.

What are the genotypes of the parents? Parents: F D x F D

Children: F dd x ffD

Slide 29

Question #5B

What are the possible phenotypes and genotypes of the children that they could produce?

Cross: FfDd x FfDd

This is a dihybrid cross

Slide 30

Question #5B

Possible gametes for both: FD Fd fD fd

FD Fd fD fd

FD FFDD FFDd FfDD FfDd

Fd FFDd FFdd FfDd Ffdd

fD FfDD FfDd ffDD ffDd

fd FfDd Ffdd ffDd ffdd

Slide 31

Question #5B

Phenotype : Freckles/Dimples: 9

Freckles/no dimples: 3

no freckles/Dimples: 3

no freckles/no dimples: 1

Phenotypic ratio will always been 9:3:3:1 for all F1 dihybrid crosses.

Slide 32

Question #5B

Genotypic ratio: FFDD - 1

FFDd - 2

FFdd - 1

FfDD - 2

FfDd - 4

Ffdd - 2

ffDD - 1

ffDd - 2

ffdd - 1

Slide 33

Question #5C

What are the chances that they would have a child whom lacks both freckles and dimples?

This child will have a genotype of ffdd

Answer: 1/16

Slide 34

Question #5D

A person with freckles and dimples whose mother lacked both freckles and dimples marries a person with freckles but not dimples whose father did not have freckles or dimples.

Cross: FfDd x Ffdd

Possible gametes:

FD Fd fD fd x Fd fd