Molecular Genetics Chapter 8

Explain why the homologous chromosomes of an inversion heterozygote can synapse only if an inversion loop forms

Homologous chromosomes need an inversion loop to allow their homologous genes to align with each other. For the inverted and noninverted regions to pair correctly, a loop must form.

Explain why the chromosomes that have balanced translocations and the normal chromosomes form a translocation cross during prophase of meiosis I.

their homologous regions are pairing with one another

A paracentric inversion

A. includes the centromere within the inverted region

B. does not include the centromere within the inverted region

C. has two adjacent inverted regions

D. is an inverted region at the very end of a chromosome

B. does not include the centromere within the inverted region

Due to crossing over within an inversion loop, a heterozygote with a pericentric inversion may produce gametes that carry

A. a deletion

B. a duplication

C. a translocation

D. both a deletion and a duplication

D. both a deletion and a duplication

A mechanism that can produce a translocation is

A. the joining of reactive ends with two different chromosomes break

B. crossing over between nonhomologous chromosomes

C. crossing over between homologous chromosomes

D. either A or B

D. the joining of reactive ends with two different chromosomes break or crossing over between nonhomologous chromosomes

Humans have 23 chromosomes per set. A person with 45 chromosomes can be described as being

A. euploid

B. aneuploid

C. monoploid

D. trisomic

B. aneuploid

In a person with trisomy 21 (Down syndrome), a genetic imbalance occurs because

A. genes on chromosome 21 are overexpressed

B. genes on chromosome 21 are underexpressed

C. genes on the other chromosomes are overexpressed

D. genes on the other chromosomes are underexpressed

A. genes on chromosome 21 are overexpresse

Humans with aneuploidy who survive usually have in inocrrect number of chromosome 13, 18, or 21 or of one of the sex chromosomes. A possible explanation why these abnormalities permit survival is because

A. the chromosomes have clusters of genes that aid in embryonic growth

B. the chromosomes are small and carry relatively few genes

C. X-chromosome inactivation allows only one X chromosome to remain active

D. both B and C are possible explanations

D. the chromosomes are small and carry relatively few genes or X-chromosome inactivation allows only one X chromosome to remain active

In a diploid species, complete nondisjunction during meiosis I may produce a viable cell that is

A. trisomic

B. haploid

C. diploid

D. triploid

C. diploid

The somatic cells of an allotetraploid contain

A. one set of chromosomes form four different species

B. two set of chromosomes from two different species

C. four sets of chromosomes from one species

D one set of chromosomes from two different species

B. two set of chromosomes from two different species