Course Guide Chapter 12: Meiosis

Question 1

What happens during meiosis I?

Answer 1

chromosomes replicate; homologous chromosomes cross over to exchange genetic material; homologs separate

Question 2

What happens during interphase I?

Answer 2

chromosomes replicate into two identical sister chromatids attached at the centromere

Question 3

What happens during prophase I?

Answer 3

condensed chromosome is attached to the nuclear envelope; homologous chromosomes align themselves and come together to form bivalents or tetrads; synapsis/crossing over occurs

Question 4

What happens during metaphase I?

Answer 4

tetrads align themselves in the middle of the cell along the metaphase plate; kinetochore fibers attached to the centromere of each pair of recombined sister chromatids to one pole; homologous chromosomes are randomly assorted during this alignment, contributing to genetic variation

Question 5

What happens during anaphase I?

Answer 5

individual pairs of sister chromatids separate from each other and go to opposite poles

Question 6

What happens during telophase I and cytokinesis I?

Answer 6

nuclear envelope may form and cleavage furrow deepens to divide the cell; in plant cells, the cell plate forms

Question 7

What happens during meiosis II?

Answer 7

the two daughter cells divide again but without DNA replication, producing four haploid cells

Question 8

What happens during interphase II?

Answer 8

sometimes seen but no DNA replication happens

Question 9

What happens during prophase II?

Answer 9

if nucleus and nucleolus are present, they disappear and spindle fibers appear

Question 10

What happens during metaphase II?

Answer 10

sister chromatids align on the metaphase plate; kinetochore fibers pointing opposite poles are attached at the centromere

Question 11

What happens during anaphase II?

Answer 11

centromeres of the sister chromatids finally separate and individual chromosomes finally move towards opposite ends

Question 12

What happens during telophase II and cytokinesis II?

Answer 12

nuclei begin to form around the chromosomes; cleavage furrow or cell plate separates the new daughter cells

Question 13

What are the causes of genetic variation in sexual reproduction?

Answer 13

1. crossing over in prophase I
2. independent assortment of chromosomes in metaphase I
3. random fertilization