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Exam 15: The Chromosomal Basis of Inheritance

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Question 1

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In a Drosophila experiment, a cross was made between homozygous wild-type females and yellow-bodied males. All of the resulting F₁s were phenotypically wild type. However, adult flies of the F₂ generation (resulting from matings of the F₁s) had the characteristics shown in the figure. - How is the mutant allele for yellow body inherited?

A) It is recessive.
B) It is codominant.
C) It is dominant.
D) It is incompletely dominant.

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A

Question 2

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The pedigree in the figure shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely ________.

A) mitochondrial
B) sex-linked dominant
C) sex-linked recessive
D) autosomal dominant

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Question 3

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What is a syndrome?

A plant-like organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine. A geneticist performed a testcross with an organism that had been found to be heterozygous for the three recessive traits, and she was able to identify progeny of the following phenotypic distribution (+ = wild type) : $\begin{array} { | l | l | l | l | l | } \hline \text { Phenotypes } & \text { Leaves } & \text { Stems } & \text { Roots } & \text { Number } \\\hline 1 & a & + & + & 14 \\\hline 2 & a & + & c & 0 \\\hline 3 & a &b &+ & 32 \\\hline 4 & a &b& c & 440 \\\hline 5 & + &b& + & 0 \\\hline 6 & + &b& c & 16 \\\hline 7 & + & + & c & 28 \\\hline 8 & + & + & + & 470 \\\hline & & & \text { Total } & 1000 \\\hline\end{array}$ - The greatest distance among the three genes is between a and c. What does this mean?

What does a recombination frequency of 50% indicate?

Why are males more often affected by sex-linked traits than females?

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?

Generally, only female cats have the tortoiseshell phenotype for fur colour. Which of the following statements explains this phenomenon?

In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure. Based on this information, what is the order of these genes on a chromosome map?

Which of the following statements would explain a testcross involving F₁ dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?

The SRY gene is best described as ________.

Which of the following occurrences describes how recombination between linked genes comes about?

Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?

Which of the following statements correctly describes the reason that closely-linked genes are typically inherited together?

A plant-like organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine. A geneticist performed a testcross with an organism that had been found to be heterozygous for the three recessive traits, and she was able to identify progeny of the following phenotypic distribution (+ = wild type) : $\begin{array} { | l | l | l | l | l | } \hline \text { Phenotypes } & \text { Leaves } & \text { Stems } & \text { Roots } & \text { Number } \\\hline 1 & a & + & + & 14 \\\hline 2 & a & + & c & 0 \\\hline 3 & a &b &+ & 32 \\\hline 4 & a &b& c & 440 \\\hline 5 & + &b& + & 0 \\\hline 6 & + &b& c & 16 \\\hline 7 & + & + & c & 28 \\\hline 8 & + & + & + & 470 \\\hline & & & \text { Total } & 1000 \\\hline\end{array}$ - What is the greatest benefit of having used a testcross for this experiment?

Which of the following phrases correctly defines what one map unit is?

Abnormal chromosomes are frequently found in malignant tumours. Errors such as translocations may place a gene in close proximity to different control regions. Which of the following events might then occur to make the cancer worse?

Duchenne muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human X chromosome. The patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein. They rarely live past their 20s. How likely is it for a woman to have this condition?

A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following statements describes her expected phenotype?

Which of the following statements correctly describes what happens to a chromosome after a nonreciprocal translocation occurs?