non-colorblind woman with a normal chin, whose mother was colorblind, marries a

Question

non-colorblind woman with a normal chin, whose mother was colorblind, marries a cleft- chinned, non-colorblind man whose mother had a normal chin. What are the expected phenotypic ratios of the children? 14. A man with a cleft chin marries a normal-chinned woman and they have 10 children, all with cleft chins. (a) Can you be sure the man is homozygous? Explain. (b) If the 11th child has a cleft chin, will that prove that the father is homozygous? Explain. (c) Assume that the father is actually Bb and has had 10 cleft-chinned children. What is the probability that the next child will have a normal chin? 15. Rex has a cleft chin and lacks perfect pitch, both autosomal traits. His wife, Mary, hasa normal chin and perfect pitch. Rex's father had a normal chin and Mary's mother lacked perfect pitch. Rex and Mary plan to have three children. What's the probability that the children all have normal chins and lack perfect pitch?

Explanation / Answer

Colourblindness is a X linked recessive disease and Cleft chin is a autosomal dominant trait

The woman is a normal chinned, non colourblind whose mother was a colourblind, so the Genotype of the woman is XX+cc [X+- Colourblind recessive allele, C- Cleft chin dominant allele, c- normal chin recessive allele]

Genotype of cleft chinned non colourblind man is XYCc

XXCc

Non colourblind Cleft chin

XXcc

Non colourblind normal chin

XYCc

Non colourblind cleft chin

XYcc

Non colorblind normal chin

XX+Cc

Non colourblind Cleft chin

XX+cc

Non colourblind normal chin

X+YCc

Colour blind Cleft chin

X+Ycc

colourblind normal chin

XXCc

Non colourblind Cleft chin

XXcc

Non colourblind normal chin

XYCc

Non colourblind cleft chin

XYcc

Non colorblind normal chin

XX+Cc

Non colourblind Cleft chin

XX+cc

Non colourblind normal chin

X+YCc

Colour blind Cleft chin

X+Ycc

colourblind normal chin

Phenotypic ratio:

Non colourblind cleft chin : Non colourblind normal chin : Colour blind cleft chin : Colourblind normal chin = 6:6:2:2

=3:3:1:1

14 a) Yes the man needs to be homozygous for all the children to be cleft chinned.

Lets say the homozygous genotype of the man is CC [as cleft chinned is a autosomal dominant allele]

Woman genotype will be cc

All the children will be homozygous with one dominant cleft chin allele so they all will be cleft chinned.

14 b) Yes if the 11th child is borned and he is also cleft chinned, it proves that 100% of the couples offsprings are cleft chinned and heterozygous. So the father has to be dominant homozygous.

14 c) If the father is Bb that is heterozygous then there is a 50% chance of any upcoming child of his to have cleft chinned-

Bb

Cleft chinned

Bb

cleft chinned

bb

normal chinned

bb

normal chinned

Phenotypic ratio: Cleft chin : normal chin= 2 : 2 = 1:1

So probability of the next child to have cleft chin is 0.5

XC Xc YC Yc Xc

XXCc

Non colourblind Cleft chin

XXcc

Non colourblind normal chin

XYCc

Non colourblind cleft chin

XYcc

Non colorblind normal chin

X+c

XX+Cc

Non colourblind Cleft chin

XX+cc

Non colourblind normal chin

X+YCc

Colour blind Cleft chin

X+Ycc

colourblind normal chin

Xc

XXCc

Non colourblind Cleft chin

XXcc

Non colourblind normal chin

XYCc

Non colourblind cleft chin

XYcc

Non colorblind normal chin

X+c

XX+Cc

Non colourblind Cleft chin

XX+cc

Non colourblind normal chin

X+YCc

Colour blind Cleft chin

X+Ycc

colourblind normal chin

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