Exam 15: The Chromosomal Basis of Inheritance

Genomic imprinting is generally due to the addition of methyl (-CH3)groups to C nucleotides in order to silence a given gene. If this depends on the sex of the parent who transmits the gene, which of the following must be True?

What proportion of their sons would be color-blind and of normal height?

Red-green color blindness is caused by a sex-linked recessive allele. A color-blind man marries a woman with normal vision whose father was color-blind. What is the probability that they will have a color-blind daughter? What is the probability that their first son will be color-blind? (Note the different wording in the two questions.)

When Thomas Hunt Morgan crossed his red-eyed F₁ generation flies to each other, the F₂ generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

A fruit fly that is True-breeding for gray body, vestigial wings (b⁺ b⁺ vg vg)is mated with one that is True-breeding for black body, normal wings (b b vg⁺ vg⁺). A)Draw the chromosomes for each P generation fly, showing the position of each allele. B)Draw the chromosomes and label the alleles for an F₁ fly. C)Suppose an F₁ female is testcrossed. Draw the chromosomes of the resulting offspring in a Punnett square like the one at the bottom of Fig. 15.10 in your textbook. D)Knowing that the distance between these two genes is 17 map units, predict the phenotypic ratios of these offspring.

Determine the sequence of genes along a chromosome based on the following recombination frequencies: A-B, 8 map units; A-C, 28 map units; A-D, 25 map units; B-C, 20 map units; B-D, 33 map units.

A man with Klinefelter syndrome (47, XXY)is expected to have any of the following EXCEPT

Sex determination in mammals is due to the SRY region of the Y chromosome. An abnormality could allow which of the following to have a male phenotype?

A couple has a child with Down syndrome when the mother is 39 years old at the time of delivery. Which is the most probable cause?

Assume that genes A and B are linked and are 50 map units apart. An animal heterozygous at both loci is crossed with one that is homozygous recessive at both loci. What percentage of the offspring will show phenotypes resulting from crossovers? If you did not know that genes A and B were linked, how would you interpret the results of this cross?

A gene is considered to be non-Mendelian in its inheritance pattern if it seems to "violate" Mendel's laws. Which of the following would then NOT be considered non-Mendelian?

How many of their daughters might be expected to be color-blind dwarfs?

What is the reason that linked genes are inherited together?

Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?

The following is a map of four genes on a chromosome: Figure 15.1 Between which two genes would you expect the highest frequency of recombination?

New combinations of linked genes are due to which of the following?

In 1956 Tijo and Levan first successfully counted human chromosomes. The reason it would have taken so many years to have done so would have included all but which of the following?

What is the chromosomal system for sex determination in birds?

An inversion in a human chromosome often results in no demonstrable phenotypic effect in the individual. What else may occur?

A certain kind of snail can have a right-handed direction of shell coiling (D)or left handed coiling (d). If direction of coiling is due to a protein deposited by the mother in the egg cytoplasm, then a Dd egg-producing snail and a dd sperm-producing snail will have offspring of which genotype(s)and phenotype(s)?