Which best describes the Chromosomal Theory of Inheritance?

1. The theory was proposed by Charles Darwin. It describes the units of inheritance between parents and offspring, as well as the processes by which those units control offspring development.
2. The theory was proposed by Boveri-Sutton. It describes linkage, recombination, and crossing over, and states that Mendelian genes have specific loci on chromosomes, which undergo segregation and independent assortment.
3. The theory was proposed by Charles Darwin. It states the Mendelian genes have two alternate forms and undergo independent assortment. It helped increase the understanding of linkage and recombination.
4. The theory was proposed by Boveri-Sutton. It describes the units of inheritance between parents and offspring as well as the processes by which those units control offspring development.

In a test cross for two characteristics (dihybrid cross), can the predicted frequency of recombinant offspring be 60 percent? Why or why not?

1. No, the predicted frequency of recombinant offspring ranges from 0 percent (for linked traits) to 50 percent (for unlinked traits) because of both parental and nonparental cases.
2. Yes, the predicted frequency of recombinant offspring can be 60 percent if genes are located very far from each other.
3. Yes, the predicted frequency can be 60 percent if crossing over occurs during every meiotic event.
4. No, the predicted frequency can never be 60 percent due to the presence of mutations such as deletions.

Which statement best describes how nondisjunction can result in an aneuploid zygote?

Figure 13.15

1. Nondisjunction only occurs when homologous chromosomes do not separate during meiosis I, resulting in the formation of gametes containing n⁺1 and n-1 chromosomes.
2. Nondisjunction only occurs when sister chromatids do not separate in meiosis II, resulting in the formation of gametes containing n⁺1 and n-1 chromosomes.
3. Nondisjunction is the failure of homologous chromosomes to separate during meiosis I or the failure of sister chromatids to separate during meiosis II, leading to the formation of n⁺1/n-1/n chromosomes.
4. Nondisjunction occurs when the sister chromatids fail to separate during mitosis II, resulting in the formation of gametes containing n⁺1 and n-1/n chromosomes.

Select the answer that correctly identifies the various chromosomal aberrations and their worst-case negative consequences.

1. nondisjunction - aneuploid gametes; duplication - physical and mental abnormalities; deletion - lethal to a diploid organism; inversion - chromosomal breaks in gene; and translocations - effects depend on how positions of genes are altered
2. nondisjunction - physical and mental abnormalities; inversion - genetic imbalance; duplication - aneuploid gametes; translocations - chromosomal breaks in the gene; and deletion - effects depend on how positions of genes are altered
3. deletion - aneuploid gametes; translocations - physical and mental abnormalities; duplication - effects depend on positions of genes; nondisjunction - causes genetic imbalance lethal to a diploid organism; and aneuploidy - leads to various syndromes
4. nondisjunction - chromosomal breaks in gene; duplication - physical and mental abnormalities; deletion - genetic imbalance lethal to a diploid organism; inversion - aneuploid gametes; and translocations - effects depend on positions of genes