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Exam 15: The Chromosomal Basis of Inheritance

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Question 1

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Use the following information to answer the questions below. A plant-like organism on the planet Pandora has 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,when a geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits,she was able to identify progeny with the following phenotypic distribution (+ = wild type) : -In which progeny phenotypes has there been recombination between genes A and B?

A) 1, 2, 5, and 6
B) 1, 3, 6, and 7
C) 2, 4, 5, and 8
D) 2, 3, 5, and 7
E) in all 8 of them

F) C) and D)
G) A) and B)

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Question 2

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If nondisjunction occurs in meiosis II during gametogenesis,what will be the result at the completion of meiosis?

A) All the gametes will be diploid.
B) Half of the gametes will be n + 1, and half will be n - 1.
C) 1/4 of the gametes will be n + 1, 1/4 will be n - 1, and 1/2 will be n.
D) There will be three extra gametes.
E) Two of the four gametes will be haploid, and two will be diploid.

F) D) and E)
G) A) and B)

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Question 3

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What is the source of the extra chromosome 21 in an individual with Down syndrome?

Refer to the following information to answer the questions below. A man who is an achondroplastic dwarf with normal vision marries a colour-blind woman of normal height.The man's father was 6 feet tall,and both the woman's parents were of average height.Achondroplastic dwarfism is autosomal dominant,and red-green colour blindness is X-linked recessive. -They have a daughter who is a dwarf with normal colour vision.What is the probability that she is heterozygous for both genes?

Calico cats are female because

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

Women (and all female mammals) have one active X chromosome per cell instead of two.What causes this?

A man who carries an allele of an X-linked gene will pass it on to whom?

Three genes at three loci are being mapped in a particular species.Each has two phenotypes,one of which is markedly different from the wild type.The unusual allele of the first gene is inherited with either of the others about 50% of the time.However,the unusual alleles of the other two genes are inherited together 14.4% of the time.Which of the following describes what is happening?

In humans,male-pattern baldness is controlled by an autosomal gene that occurs in two allelic forms.Allele Hn determines nonbaldness,and allele Hb determines pattern baldness.In males,because of the presence of testosterone,allele Hb is dominant over Hn.If a man and woman both with genotype HnHb have a son,what is the chance that he will eventually be bald?

A recessive allele on the X chromosome is responsible for red-green color blindness in humans.A woman with normal vision whose father is color blind marries a color-blind male.What is the probability that this couple's first son will be color blind?

Thomas Hunt Morgan's choice of Drosophila melanogaster has been proven to be useful even today.Which of the following has/have continued to make it a most useful species? I.its four pairs of chromosomes II.a very large number of visible as well as biochemically mutant phenotypes III.easy and inexpensive maintenance IV.short generation time and large number of offspring

Which of the following statements is true of linkage?

Chimpanzees,gorillas,and orangutans have DNA sequences that are almost identical to those of humans; however,these genes are found on 24 pairs of chromosomes in apes,while humans have 23 pairs.The C2 chromosome in humans is a large chromosome with similar banding pattern and DNA sequences to two smaller chromosomes in apes (C2 and C4) .In addition it appears to have both a vestigial second centromere and telomere sequences in the middle of the strand. -It is believed that early hominins interbred with each other.Ancient humans may have successfully mated with both Neanderthal and Denisovans.What must be true of these species for this to occur? They must have

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome.What is this alteration called?

Males are more often affected by sex-linked traits than females because

In birds,sex is determined by a ZW chromosome scheme.Males are ZZ and females are ZW.A recessive lethal allele that causes death of the embryo is sometimes present on the Z chromosome in pigeons.What would be the sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a normal female?

At what point in cell division is a chromosome lost so that,after fertilization with a normal gamete,the result is an embryo with 45,X? I.an error in anaphase I II.an error in anaphase II III.an error of the first postfertilization mitosis IV.an error in pairing

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?

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