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Exam 8: Chromosome Variation

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Question 31

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Explain the genetic basis for sterility in autopolyploid organisms.

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Autopolyploid organisms are those that h...

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Question 32

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Which type of aneuploidy is represented in gametes labeled A in the figure?

A) nullisomy
B) monosomy
C) trisomy
D) tetrasomy

E) C) and D)
F) All of the above

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Question 33

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In rare cases some children that express recessive genetic diseases, such as cystic fibrosis, have only one parent that is heterozygous for the disease allele. If the parents are the true biological parents of the affected child, offer a genetic explanation for this observation.

A woman has a condition where all of her gametes undergo nondisjunction of chromosome 21 in meiosis I, but meiosis II proceeds normally. She mates with a man who produces all normal gametes. What is the probability that the fertilized egg will develop into a child with Down syndrome? Assume that all gametes and zygotes are viable.

What type of organism results from the hybridization of a haploid gamete from one species with a diploid gamete from a different species?

What typically happens to the small fragment generated by a Robertsonian translocation?

The centromere is located approximately in the middle of which type of chromosome?

Wild-type Arabidopsis has 5 chromosomes (2n = 10) . Trisomic plants are designated as "Tr" followed by the trisomic chromosome number-that is, Tr1 is trisomic for chromosome 1. Assuming that trisomy is fully viable and that all possible pairing configurations (including nonpairing) are possible at meiosis, what proportion of the progeny from the cross wt × Tr1;Tr2 will have a wild-type chromosomal complement?

Species I is diploid (2n = 6) with chromosomes AABBCC; a related species II is diploid (2n = 6) with chromosomes MMNNOO. Indicate the chromosomes that would be found in individuals with the following chromosome mutations. a. trisomic for chromosome A b. tetrasomic for chromosome N c. an autotriploid of species I d. an allotetraploid e. an autotetraploid of species II f. monosomic for chromosome B g. a double trisomic for chromosomes A and C h. a nullisomic for chromosome O

An individual that is heterozygous for a paracentric inversion has the following chromosomes: A B • C D E F G H I A B • C F E D G H I a. Sketch the pairing of these two chromosomes during prophase I of meiosis, showing all four strands. b. Draw the chromosomes that would ultimately result from a single crossover between the E and F segments. c. What will happen when the chromosomes separate in anaphase I of meiosis?

Species A and B are closely related. Species A has 2n = 12 chromosomes, and species B has 2n = 14 chromosomes. Chromosome numbers (2n) for the following related species are thought to have arisen through polyploidy. For each species, indicate what type of polyploid it is, and how it may have formed. a. Species C 18 b. Species D 24 c. Species E 26 d. Species F 28 e. Species G 36 f. Species H 52 g. Species I 56

Wild-type Arabidopsis has 5 chromosomes (2n = 10) . Trisomic plants are designated as "Tr" followed by the trisomic chromosome number-that is, Tr1 is trisomic for chromosome 1. Assuming that trisomy is fully viable and that all possible pairing configurations (including nonpairing) are possible at meiosis, what proportion of the progeny from the cross Tr1 × Tr1 will have a wild-type chromosomal complement?

Chimpanzees, gorillas, and orangutans all have 48 chromosomes, whereas humans have 46. Human chromosome 2 is a large, metacentric chromosome with G-banding patterns that closely match those found on two different acrocentric chromosomes of the apes. Which statement would BEST explain these findings?

How can a chromosome deletion be detected?

Which type of chromosome mutation DECREASES the amount of genetic material?

Two nonhomologous chromosomes have the following segments: A • B C D E F G R • S T U V W X Draw chromosomes that would result from the following chromosome rearrangements. a. Reciprocal translocation of CD and TU b. Reciprocal translocation of CD and W c. Robertsonian translocation

You are studying two different mutant fish lines (A and B). You suspect that both have mutations that cause nondisjunction for a particular chromosome, which when aneuploid results in an altered egg phenotype. You notice that all of the eggs from the A mutants have the altered phenotype. In contrast, only half the eggs laid by B mutants have the altered phenotype. If you are right and the mutants are suffering nondisjunction during meiosis, what could explain the frequency difference in egg phenotype?

Which type of chromosome mutation results in a chromosome segment that is turned 180 degrees?

A female rat that is heterozygous for an autosomal reciprocal translocation has 36 eggs that were generated from the following 9 meioses: 4 by alternate segregation, 4 by adjacent-1 segregation, and 1 by adjacent-2 segregation. She is mated to a chromosomally wild-type male. What is the probability that her offspring will inherit a chromosome bearing the translocation?

Isochromosomes have the structure ABC $\bullet$ CBA (where $\bullet$ represents the centromere and A, B, and C represent wild-type alleles of three different genes). In some cases, such isochromosomes are derived from two copies of one half of a metacentric chromosome, which has a centromere near its center. For example, a wild-type metacentric chromosome ABC $\bullet$ DEF might form two distinct isochromosomes, ABC $\bullet$ CBA and FED $\bullet$ DEF. The centromeres of such distinct isochromosomes can be homologous so that they cause the segregation of the two distinct isochromosomes from each other during meiosis. a. A mutant of genotype ABC $\bullet$ CBA / FED $\bullet$ DEF is viable. If you cross this mutant with a wild-type individual, what would you expect to be the genotype of the offspring? Would these offspring be viable or not? Explain. b. What would you expect if you cross this mutant with another individual of genotype ABC $\bullet$ CBA / FED $\bullet$ DEF? Explain. c. You are given a pericentric inversion mutant in which this same chromosome is of genotype ABD $\bullet$ CEF. In an individual heterozygous for this inversion and a wild-type chromosome there is a crossover between C and the centromere. Draw the crossover event and indicate the gametes that would be generated. d. Assume that the inversion interval is very small so that both duplications and deletions for this interval (from C to D) do not cause inviability. Indicate the gentoypes expected in offspring of a cross between the inversion heterozygote and an individual of genotype ABC $\bullet$ CBA / FED $\bullet$ DEF.