Mastering 9

Which list of steps in the eukaryotic cell cycle is given in the correct order?

. . . G1 - S - G2 - M - G1 . . . The S phase is both preceded and followed by a period of growth (G1 and G2, respectively). After the M phase, the cell re-enters the G1 phase.

A cell has 16 chromosomes. How many chromosomes would its daughter cells have after meiosis?

8 Meiosis reduces the number of chromosomes passed on to daughter cells by one-half.

The parent cell that enters meiosis is diploid, whereas the four daughter cells that result are haploid.

DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II. During anaphase of both meiosis I and meiosis II, the DNA content (number of copies of chromosomes) in a cell is halved. However, the ploidy level changes only when the number of unique chromosome sets in the cell changes. This occurs only in meiosis I (where separation of homologous chromosomes decreases the ploidy level from 2n to n and produces daughter cells with a single chromosome set).

True or False? A dyad is composed of two homologous chromosomes joined at a common centromere.

False A dyad is composed of two sister chromatids joined at a common centromere.

Synapsis

Point-by-point pairing of homologous chromosomes during prophase of meiosis I.

Which of the following statements about meiosis is true?

The second meiotic division is similar to mitosis in that the sister chromatids separate. The second meiotic division is also called an equational division and involves the separation of sister chromatids, similar to what occurs in mitosis.

True or False? A chromosome may contain one or two chromatids in different phases of the mitotic or meiotic cell cycle.

True

True or False? If a typical G1 nucleus is 2n and contains 2C (two complements) of DNA, a prophase I cell is 2n and contains 4C of DNA.

True

True or False? S phase is the part of interphase when DNA duplication takes place.

True

Sister chromatids

are the "post-S phase" structure of replicated chromosomes. Also called dyads Because they are composed of two chromatids joined by a centromere

Unlike with asexual reproduction, offspring of sexual reproduction are genetically different from each other and from both of their parents. Mechanisms that contribute to genetic variation include

errors (mutations) that occur during DNA replication the production of recombinant chromosomes due to crossing over the independent assortment of homologous chromosomes in meiosis I the separation of sister chromatids (which are no longer identical due to crossing over) in meiosis II the random fusion of male and female gametes during fertilization

Crossing over

exchange of genetic material between chromatids

chiasmata

refers to the structure, when viewed microscopically, of crossed chromatids.

Monad

sister chromatid

Bivalent

structures formed by the synapsis of homologous chromosomes.

Tetrads

synapsed homologous chromosomes, which are composed of four chromatids.