Exam 15: The Chromosomal Basis of Inheritance

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

A homozygous tomato plant with red fruit and yellow flowers was crossed with a homozygous tomato plant with golden fruit and white flowers. The F1 all had red fruit and yellow flowers. The F1 were testcrossed by crossing them to homozygous recessive individuals, and the following offspring were obtained: Red fruit and yellow flowers-41 Red fruit and white flowers-7 Golden fruit and yellow flowers-8 Golden fruit and white flowers-44 How many map units separate these genes?

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

Which of the following statements correctly describes the meaning of the chromosome theory of inheritance as expressed in the early 20th century?

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?

Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?

A certain kind of snail can have a right-handed direction of shell coiling (DD or Dd) or left-handed coiling (dd). However, 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)?

What is an adaptive advantage of recombination between linked genes?

Red-green colour blindness is a sex-linked recessive trait in humans. Two people with normal colour vision have a colour-blind son. What are the genotypes of the parents?

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?

Cinnabar eye colour is a sex-linked, recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes?

Which of the following is an example of monosomy in humans?

Inheritance patterns cannot always be explained by Mendel's models of inheritance. If a pair of homologous chromosomes fails to separate during meiosis I, select the choice that shows the chromosome number of the four resulting gametes with respect to the normal haploid number (n)?

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

If cell X enters meiosis, and nondisjunction of one chromosome occurs in one of its daughter cells during meiosis II, how will this affect the gametes at the completion of meiosis?

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): Phenotypes Leaves Stems Roots Number 1 a + + 14 2 a + c 0 3 a b + 32 4 a b c 440 5 + b + 0 6 + b c 16 7 + + c 28 8 + + + 470 Total 1000 - If recombination frequency is equal to distance in map units, what is the approximate distance between genes A and B?

In humans, clear gender differentiation occurs not at fertilisation, but after the second month of gestation. Which of the following statements describes the first event of this differentiation?

All female mammals have one active X chromosome per cell instead of two. What causes this to happen?

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as an X-linked recessive allele in humans. A woman whose father suffered from G6PD marries a man who has the disease. What proportion of their sons would have the disease?

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): Phenotypes Leaves Stems Roots Number 1 a + + 14 2 a + c 0 3 a b + 32 4 a b c 440 5 + b + 0 6 + b c 16 7 + + c 28 8 + + + 470 Total 1000 - Which of the following are the phenotypes of the parents in this cross?