9.6.2 The Bombay Phenotype: Infidelity or Epistasis? Flashcards Preview

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Flashcards in 9.6.2 The Bombay Phenotype: Infidelity or Epistasis? Deck (15)
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1
Q

note

A

• Review: In humans, three alleles are responsible for the blood groups.
• A second gene also affects the inheritance of blood groups. Epistasis describes the interaction between the two genes.
• In the presence of the dominant H allele, a protein precursor is converted to A or B antigens. When the genotype is hh, the precursor is not converted, resulting in type O blood, regardless of the presence of A or B antigens.
- Review: In epistasis, two genes assort independently of one another, but the dominant allele for one gene may not be expressed because the second gene masks it. Epistasis is involved in determining coat color of mice.
- Review: In humans, three alleles are responsible for the blood groups.
- The Bombay phenotype was named for a perplexing situation involving blood types in a family in Bombay, India. A type O woman married a type A man. Their first child had type O blood. Based on what was understood about blood types, her genotype was determined to be “ii” and his to be “IAi”. Their second child had type AB blood. Once infidelity was ruled out, an alternate explanation was needed.
- The unlikely pattern of inheritance was actually caused by epistatic interactions between molecules.
- A second gene determines antigenic expression at the locus for blood type antigens. Individuals who are hh for this locus will have type O blood no matter what their genotype is at the other locus. For example, the F1 woman is type O, but she carries the IB allele at the other locus. The AB son in the F2 received a B allele from the mother and an A allele from the father. He received an H allele from the father and an h allele from the mother. Because he carries the dominant H allele, his AB genes at the other locus are expressed

2
Q

Which of the following is used to trace the inheritance of genetic traits and disorders throughout generations?

A
  • pedigree chart
3
Q

The Bombay phenotype is representative of a class of genetic systems that are involved in the control of a series of pathways each dependent on the previous for product. As an example, consider the following system of control of flower color in a plant:

The genes each have two alleles:

A = blue pigment
a = defective, no pigment
B = red pigment
b = defective, no pigment

What color flowers do the offspring of this cross have:

AaBB × Aabb

A
  • purple, red
4
Q

How many sets of alleles are responsible for blood type in humans?

A
  • 2
5
Q

Which of the following could be explained by the Bombay phenotype?

A
  • An individual with the I AI A genotype has Type O blood
6
Q

The Bombay phenotype was a result of what genetic occurrence?

A
  • epistasis
7
Q

If a child has blood Type O, and both parents have Type AB blood, what are the possible genotypes the child could have?

A
  • I AI Ahh, I AI Bhh, I BI Bhh
8
Q

The Bombay phenotype is representative of a class of genetic systems that are involved in the control of a series of pathways each dependent on the previous for product. As an example, consider the following system of control of flower color in a plant:

The genes each have two alleles:

A = blue pigment
a = defective, no pigment
B = red pigment
b = defective, no pigment

What color flowers do the offspring of this cross have:

AaBb × Aabb

A
  • red, white, purple, blue
9
Q

In 1918, a geneticist named R.A. Emerson crossed two pure-breeding varieties of yellow corn. All of the F1 plants produced purple, not yellow, kernels. When two of the F1 plants were crossed, 56% of the kernels were purple and kernels 44% were yellow. From these findings, what can you deduce about the mode of inheritance of kernel color in corn?

A
  • The F2 results show a modified 9:3:3:1 ratio, indicating that two gene loci are involved, and epistasis is occurring.
10
Q

Which of the following is a description of the role of epistasis in producing human blood type phenotypes?

A
  • Blood type phenotype is controlled by the interaction of more than one set of alleles.
11
Q

A geneticist crosses a red-flowered line and a white-flowered line of a particular species of orchid and the following results are obtained:
P pure line 1 × pure line 2
F1 all white
F2 131 white : 29 red
With regard to the mode of inheritance of flower color, which of the following statements is false?

A
  • The homozygous recessive for one trait and the heterozygous for the other trait results in red flowers.
12
Q

The Bombay phenotype is an example of

A
  • epistasis
13
Q

The H gene codes for the precursor to the blood antigens that determine blood type. Dominant H allows precursor formation. What phenotype would a person with the genotype I AI BHh have?

A
  • Type AB blood
14
Q

Could the cross I AI BHH × I AiHh produce an offspring with Type O blood? Why or why not?

A
  • No, these parents could not produce offspring with the ii genotype or the genotype that would prevent protein precursor conversion.
15
Q

If a person with the genotype I AI AHh has children with a person with the genotype I BI BHh, what are the possible blood type phenotypes of the offspring?

A
  • Type AB or Type O

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