Exam 8: Chromosome Mutations: Variation in Number and Arrangement

A genomic condition that may be responsible for some forms of fragile X syndrome, as well as Huntington disease, involves ________.

The chromosomal aberration that causes cri du chat syndrome can be referred to as a segmental deletion.

Clearly illustrate the pairing configuration of an inversion (paracentric) heterokaryotype.

Fragile X syndrome (or Martin-Bell syndrome) is the most common form of inherited mental retardation in humans. Is it more common in males or females? What is FMR1?

Translocations may be pericentric or paracentric.

A position effect occurs when a gene's expression is altered by virtue of a change in its position. One might expect position effects to occur with inversions and translocations.

Describe Bar mutations in Drosophila melanogaster.

A pericentric inversion includes the centromere.

An individual with Patau syndrome would be called a triploid.

Describe the maternal age effect associated with Down syndrome.

The term aneuploidy is synonymous with the term segmental deletion.

Although the most frequent forms of Down syndrome are caused by a random error, nondisjunction of chromosome 21, Down syndrome occasionally runs in families. The cause of this form of familial Down syndrome is ________.

Deletions are chromosomal aberrations in which some portion of a chromosome is missing. Describe a method using Drosophila deletions to determine the actual, physical location of a gene.

Familial Down syndrome is caused by a translocation involving chromosome 21.

Trisomics are observed in humans; monosomics are not. Why?

In Drosophila melanogaster (2n = 8), a fly with seven chromosomes could be called a haplo-IV.

Individuals with familial Down syndrome are trisomic and have 47 chromosomes.

Inversion heterokaryotypes are often characterized as having reduced crossing over and reduced fertility. Assume that you were examining a strain of organisms you knew to be inversion heterokaryotypes and saw a relatively high number of double chromatid bridges extending between anaphase I nuclei. What would be a likely explanation for this observation? Explain with a labeled diagram.

Assume that a species has a diploid chromosome number of 24. The term applied to an individual with 36 chromosomes would be triploid.

Trisomy 21, or Down syndrome, occurs when there is a normal diploid chromosomal complement but one (extra) chromosome 21. While there is reduced fertility in both sexes, females have higher fertility than males. Van Dyke et al. (1995; Down Syndrome Research and Practice 3(2):65-69) summarize data involving children born of Down syndrome individuals. Given the fact that conceptuses with 48 chromosomes (four #21 chromosomes) are not likely to survive early development, what percentage of surviving offspring would be expected to have Down syndrome if both parents have Down syndrome?