In man, two abnormal conditions, cataracts (C) in the eyes and excessive fragility (F) in the bones, seem to depend on separate dominant genes located on different chromosomes. Normal vision and normal bones are recessive traits. A man with cataracts and normal bones, whose father had normal eyes, married a woman free from cataracts but with fragile bones. Her father had normal bones. _________ What is the genotype of the man with cataracts and normal bones? _________ What is the genotype of the woman with normal vision and fragile bones?
Answers
Answer:
1. Cc ff
2. cc Ff
3. F1) 4/16 = 1/2 = 25% CcFf, cataracts and fragile bones
4/16 = 1/2 = 25% Ccff, cataracts and normal bones
4/16 = 1/2 = 25% ccFf, normal eyes and fragile bones
4/16 = 1/2 = 25% ccff normal eyes, normal bones
Explanation:
Available data:
two genes located on different chromosomes
cataracts (C) in the eyes is dominant over Normal vision
excessive fragility (F) in the bones is dominant over Normal bones
man with cataracts and normal bones
man´s father had normal eyes
woman free from cataracts but with fragile bones
woman´s father had normal bones
1. What is the genotype of the man with cataracts and normal bones?
The man has normal bones, so his genotype for this trait is ff, because normal bones is a
recessive trait.
The man has cataracts, but his father had normal eyes, which means that he was
homozygous recessive for the trait, cc. The man received one allele from his father and one
allele from his mother. He must have received a recessive allele from his father and a
dominant allele from his mother. So the man´s genotype for this trait is Cc.
Then, the genotype of the man is Cc ff
What is the genotype of the woman with normal vision and fragile bones?
The woman has normal vision, so her genotype for this trait is cc, because normal vision is
a recessive trait.
The woman has fragile bones, but her father had normal bones, which means that he was
homozygous recessive for the trait, ff. The woman received one allele from her father and
one allele from her mother. She must have received a recessive allele from her father and a
dominant allele from her mother. So the woman´s genotype for this trait is Ff.
Then, the genotype of the woman is cc Ff
3. What type of offspring might this couple expect?
Cross: woman man
Parentals) ccFf x Ccff
Gametes) cF cF cf cf Cf cf Cf cf
Punnett square) cF cF cf cf
Cf CcFf CcFf Ccff Ccff
Cf CcFf CcFf Ccff Ccff
cf ccFf ccFf ccff ccff
cf ccFf ccFf ccff ccff
F1) 4/16 = 1/2 = 25% CcFf, cataracts and fragile bones
4/16 = 1/2 = 25% Ccff, cataracts and normal bones
4/16 = 1/2 = 25% ccFf, normal eyes and fragile bones
4/16 ccff = 1/2 = 25% normal eyes, normal bones