Question

Practice Problems for Bio 1:

1) Short hair is dominant over long hair in dogs. If a short-haired dog whose mother was long-haired is crossed with a long-haired dog, what proportion of the offspring will be short-haired?

2) The common grackle is a species of robin-sized blackbirds that are fairly common over most of the United States. Suppose that long tails (L) were dominant to short tails in these birds. A female short-tailed grackle mates with a male long-tailed grackle who had one parent with a long tail and one parent with a short tail. What is the male's genotype? What is the genotypic ratio?

2) A man with type O blood has a sister with type AB blood. What are the genotypes and phenotypes of their parents?

3) The inheritance of curly hair illustrates incomplete dominance. When a curly haired individual reproduces with a straight-haired one, the children all have wavy hair. What offspring would be produced, in what proportions, when two people with wavy hair reproduce?

4) Colorblindness is an X-linked trait recessive disorder. A woman who does not carry the color-blindness allele has children with a man who is color blind. What proportion of their children will be color blind?

5) Huntington disease (HD) is an autosomal dominant disorder. A person who is heterozygous for the Huntington disease allele has offspring with someone who does not have HD. What proportion of their children will have HD?

Answer 1

1) let the alleles be S- short-haired, s- long-haired.

the genotype of the short-haired dog whose mother was long-haired, is Ss, because its mother has long hair so her genotype is ss, so she can pass only s allele to the progeny so genotype of progeny is Ss, since the dog is short-haired it has the dominant allele S and also has recessive allele s inherited from mother.

The genotype of long-haired dog is ss.

Ss * ss

	S	s
s	Ss (short haired)	ss ( long-haired)
s	Ss ( short haired)	ss ( long-haired)

the proportion of short-haired progeny= number of short haired progeny/total number of progeny=2/4=1/2

2) alleles are L- long tail , l- short tail.

the genotype of female with short tails is ll and genotype of the male long-tailed grackle who had one parent with a long tail and one parent with a short tail is Ll, male has inherited l allele from the parent having short tail (ll).

Ll * ll

	L	l
l	Ll ( long tail)	ll ( short tail)
l	Ll (long tail)	ll ( short tail)

genotypic ratio is

Ll: ll=1:1