ch11: meiosis and sexual reproduction

Question 1

sexual reproduction combines —— from two parents through —–

Answer 1

haploid cells; fertilization

Question 2

what results from meiosis

Answer 2

four genetically different haploid cells

Question 3

what happens to the chromosomes number before fusing into the cell during meiosis

Answer 3

it cuts in half
2n –> n

Question 4

meiosis includes —- round of DNA replication and —- rounds of division

Answer 4

one; two

Question 5

meiosis one (two bullet points)

Answer 5

• preceded by normal interphase (G1, S, G2)
• chromsome replication in S phase makes identical SISTER CHROMATIDS which remain attached at the centromere

Question 6

prophase one

Answer 6

homologous chromosomes pair and the synpatonemal complex holds them together in synapsis (laying one ontop of the other, connected at the kineotochore)

Question 7

segments of chromosomes can be exchanged through

Answer 7

crossing over

Question 8

chiasmata

Answer 8

visible structures at cross over points; helps homologues stay physically connected during prophase/metaphase 1; doesnt completely separate until anaphase 1

Question 9

the four chromatids held together

Answer 9

tetrad

Question 10

metaphase one (two bullet points)

Answer 10

-homologous chromosomes move to the metaphase plate together, with kinetochores facing opposite poles
-maternal and paternal chromatids align randomly and are mixed when they migrate to the poles, creating genetic variation in daughter cells

Question 11

anaphase one (three bullet points)

Answer 11

• microtubules pull tetrads apart
• chiasmata break but sister chromatids remain attached at the centromere
• homologues separate and move toward opposite poles

Question 12

telophase one (five bullet points)

Answer 12

• separated chromosomes arrive at opposite poles
• each pole has a complete haploid set of chromosomes
• cytokinesis may or may not occur (separation of cytoplasmic contents into daughter cells)
• sister chromatids are no longer identical because of crossing over
• meiosis 2 will occur afterwards

Question 13

meiosis 2

Answer 13

looks like mitosis but without starting off with a DNA replication step

Question 14

final results of meiosis

Answer 14

• four cells containing haploid (n) sets of chromosomes
• develop directly into gametes for animals

Question 15

meiosis is characterized by four features

Answer 15

1. synapsis and crossing over
2. sister chromatids remain joined at their centromeres throughout meiosis one
3. kinetochores of sister chromatids attach to the same pole in meiosis one
4. DNA replication is suppressed between meiosis one and two

Question 16

nondisjunction

Answer 16

failure of chromosomes to move to opposite poles during either meiotic division

Question 17

aneuploid gametes

Answer 17

gametes with missing or extra chromosomes (down syndrome)