Notes

1) The stages of meiosis are classified into two divisions: meiosis I and meiosis II. Compare and contrast these two divisions.
Both meiosis I and meiosis II contain a prophase, a metaphase, and an anaphase. However, chromosomes replicate prior to meiosis I but not prior to meiosis II. Also, during meiosis I, tetrads form and align along the center of the cell. Then, the homologous chromosomes are separated and two haploid daughter cells form. During meiosis II, sister chromatids align along the center of the cell and are then separated. Four haploid daughter cells form.
2) Suppose the homologous chromosomes that make up a tetrad fail to separate during anaphase I of meiosis. Predict the results of this event.
If the homologous chromosomes of a tetrad fail to separate, half the gametes formed will have an extra chromosome. The other half will lack a chromosome. When one of these gametes fuses with a normal gamete during fertilization, the offspring will have an abnormal number of chromosomes (not 2N) in its cell
3) What might happen if the gametes of a species had the same number of chromosomes as the species’ body cells?
When the gametes fused during fertilization, the offspring would have more chromosomes in their body cells than their parents have. As a result, the species’ chromosome number would not be constant.
4) Explain why the daughter cells produced by meiosis are genetically different from each other, whereas the daughter cells produced by mitosis are not?
During meiosis, the pairs of homologous chromosomes in the parent cell form tetrads and then separate. As a result, each daughter cell receives only one chromosome from each homologous pair, and the particular chromosomes that it receives are random. Thus, each daughter cell has a different combination of chromosomes. Also, crossing-over may occur during meiosis and may result in new combinations of alleles on the chromosomes in the daughter cells. In contrast, during mitosis, homologous chromosomes usually do not form tetrads and separate, and therefore crossing-over usually does not occur.
5) Contrast the cells produced by mitosis with those produced by meiosis.
Mitosis produces diploid body cells, whereas meiosis produces haploid gametes.
6) Crossing-over rarely occurs in mitosis, unlike meiosis. Which of the following is the likely reason?
b.Homologous chromosomes rarely line up to form tetrads during mitosis.
7) Crossing-over occurs during the stage of meiosis called prophase I.
true
8) If an organism is heterozygous for a particular gene, the two different alleles will be separated during anaphase II of meiosis, assuming that no crossing-over has occurred.
false
9) An organism’s gametes have double the number of chromosomes found in the organism’s body cells.
false
10) Please select the word from the list that best fits the definition.
diploid
11) The nuclear membrane disappears during which phase of meiosis?
prophase
12) How is the chromosome number reduced between meiosis I and meiosis II?
no replication
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