GRE Subject Test: Biology : Understanding Karyotypes and Chromosomes

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Karyotypes And Chromosomes

Human beings have diploid cells. What is indicated by this statement?

Possible Answers:

Humans have two stages of cell division

Humans have both sex chromosomes and somatic chromosomes

Humans have homologous chromosome pairs

Humans have two chromosomes in each cell nucleus

Correct answer:

Humans have homologous chromosome pairs

Explanation:

Human beings have somatic (body) cells that are diploid. This means that each cell has two copies of each of the 23 chromosomes: one from the father and one from the mother. As a result, the karyotype of a human being would show 23 pairs of chromosomes, for a total of 46. Diploid cells contain two non-identical copies of the same genes. All diploid cells will contain two separate alleles for each gene in the genome, represented by the two homologous chromosomes.

An important note to make is that human germ (sex) cells are haploid, meaning that the chromosomes are not paired in sperm cells and egg cells.

Example Question #1 : Understanding Karyotypes And Chromosomes

Which correctly describes eukaryotic histones in a nucleosome structure?

Possible Answers:

A core histone nonamer

A core histone plus a linker histone octamer

A core histone heptamer plus a linker histone

A core histone octamer plus a linker histone

A core histone octamer plus 2 linker histones

Correct answer:

A core histone octamer plus a linker histone

Explanation:

A nucleosome is defined as a core region of histones plus one stretch of linker DNA. This gives a "beads on a string" shape, which can be further packaged into chromatin. These nucleosomes contain a DNA wrapped histone octamer in the core region, and a linker histone in the linker DNA region. The histone octamer has 2 each of H2A, H2B, H3, and H4 histones. The linker DNA has an H1 histone. 

Example Question #3 : Understanding Karyotypes And Chromosomes

Which of the following are not observed when performing a karyotype?

Possible Answers:

Gene loci

Position of centromeres

Differences in satellite chromosome position and number 

Number of chromosomes

Size of chromosomes

Correct answer:

Gene loci

Explanation:

Karyotypes describe whole chromosome structure, including the number and size of chromosomes, position of centromeres, distribution of heterochromatin versus euchromatin, and the presence of satellite chromosomes that are found near the centromeres. However, a karyotype is unable to label specific gene sequences and determine their chromosomal locations. Most karyotypes depict chromosomes of a cell in metaphase.

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