Biology Exam 4 Pt. 2

1. A woman of blood group A has a child with a man of blood group B. The child's blood is type O. What must be the genotype of the parents?

Mother: I(A)I(A); father I(B)I(A)

Mother: I(A)i(O); father: I(B)I(B)

Mother: I(A)i(O); father I(B)i(O)

Mother: I(A)i(O); father I(B)I(B)

It is impossible for these individuals to have a chlld with type O blood.

The child's blood type O indicates that both parents must have the recessive allele for blood type O. The mother's genotype is I(A)i(O), meaning she has one dominant allele for blood type A and one recessive allele for blood type O. The father's genotype is I(B)i(O), meaning he has one dominant allele for blood type B and one recessive allele for blood type O. This combination allows for the possibility of the child inheriting two recessive alleles for blood type O, resulting in their blood type.

Explanation

The child's blood type O indicates that both parents must have the recessive allele for blood type O. The mother's genotype is I(A)i(O), meaning she has one dominant allele for blood type A and one recessive allele for blood type O. The father's genotype is I(B)i(O), meaning he has one dominant allele for blood type B and one recessive allele for blood type O. This combination allows for the possibility of the child inheriting two recessive alleles for blood type O, resulting in their blood type.

2. Cocominance

Is when heterozygotes show a phenotype intermediate between those of the two homozygotes.

Involves the expression of both alleles at a locus producing two different phenotypes.

Is only found in mammalian enzyme production.

Involves one allele having more than one phenotypic effect.

Would result in pink flowers from a cross between white and red flowers.

Cocominance is a genetic phenomenon where both alleles at a specific locus are expressed, resulting in the production of two different phenotypes in heterozygotes. This means that neither allele is dominant or recessive over the other, and both are fully expressed. It is not limited to mammalian enzyme production and can occur in various organisms. In the case of flower color, if cocominance is present, a cross between white and red flowers would result in offspring with pink flowers, as both the white and red alleles would be expressed simultaneously.

Explanation

Cocominance is a genetic phenomenon where both alleles at a specific locus are expressed, resulting in the production of two different phenotypes in heterozygotes. This means that neither allele is dominant or recessive over the other, and both are fully expressed. It is not limited to mammalian enzyme production and can occur in various organisms. In the case of flower color, if cocominance is present, a cross between white and red flowers would result in offspring with pink flowers, as both the white and red alleles would be expressed simultaneously.

3. In Mendel's experiments, if the allele for tall (7) plants was incompletely dominant over the allele for short (t) plants, what offspring would have resulted from crossing two Tt plants?

1/4 tall; 1/2 intermediate height; 1/4 short

1/2 tall; 1/4 intermediate height; 1/4 short

1/4 tall; 1/4 intermediate height; 1/2 short

All tall offspring

All intermediate height offspring

When the allele for tall plants is incompletely dominant over the allele for short plants, the offspring resulting from crossing two Tt plants would show a phenotype that is a blend of the two parental phenotypes. This is known as incomplete dominance. In this case, 1/4 of the offspring would be tall (TT), 1/2 would have an intermediate height (Tt), and 1/4 would be short (tt).

Explanation

When the allele for tall plants is incompletely dominant over the allele for short plants, the offspring resulting from crossing two Tt plants would show a phenotype that is a blend of the two parental phenotypes. This is known as incomplete dominance. In this case, 1/4 of the offspring would be tall (TT), 1/2 would have an intermediate height (Tt), and 1/4 would be short (tt).

4. Classical albinism results from a recessive allele. Which of the following is the expected ratio for the progeny when a normally pigmented male with an albino father has children with an albino woman?

3/4 normal; 1/4 albino

3/4 albino; 1/4 normal

1/2 normal; 1/2 albino

All normal

All albino

When a normally pigmented male with an albino father has children with an albino woman, the expected ratio for the progeny is 1/2 normal and 1/2 albino. This is because the albino father must carry the recessive allele for albinism, and when he passes it on to his son, the son becomes a carrier of the allele. When the carrier son then has children with an albino woman, there is a 50% chance that he will pass on the normal allele and a 50% chance that he will pass on the recessive allele, resulting in a 1/2 normal and 1/2 albino ratio for the progeny.

Explanation

When a normally pigmented male with an albino father has children with an albino woman, the expected ratio for the progeny is 1/2 normal and 1/2 albino. This is because the albino father must carry the recessive allele for albinism, and when he passes it on to his son, the son becomes a carrier of the allele. When the carrier son then has children with an albino woman, there is a 50% chance that he will pass on the normal allele and a 50% chance that he will pass on the recessive allele, resulting in a 1/2 normal and 1/2 albino ratio for the progeny.

5. A human male carrying an allele for a trait on the X chromosome is

Heterozygous.

Homozygous.

Hemizygous.

Monozygous.

Holozygous.

A human male carries only one X chromosome and one Y chromosome, while a female carries two X chromosomes. Since the allele for the trait is located on the X chromosome, a male can only have one copy of that allele. Therefore, the term "hemizygous" is used to describe males in this context, as they have only one copy of the allele on the X chromosome.

Explanation

A human male carries only one X chromosome and one Y chromosome, while a female carries two X chromosomes. Since the allele for the trait is located on the X chromosome, a male can only have one copy of that allele. Therefore, the term "hemizygous" is used to describe males in this context, as they have only one copy of the allele on the X chromosome.