10.1 Meiosis

Question 1

what is interphase?

Answer 1

• active period that precedes meiosis and involves key events needed to prepare the cell for successful division

Question 2

what occurs in Sphase of interphase?

Answer 2

DNA is replicated - chromosomes containing 2 identical DNA strands

Question 3

what are sister chromatids? (2)

Answer 3

genetically identical strands held together by centromere (central region) result of Sphase
- they separate in meiosis 2 (becoming independent chromosomes each made of single DNA strand)

Question 4

what evidence suggests that meiosis evolved from mitosis? and benefit?

Answer 4

• the fact that DNA replication occurs prior to meiosis
• one benefit of duplication of chromatids is that it increase the potential for genetic recombination to occur (more variation)

Question 5

what is the second growth phase called?

Answer 5

interkinesis (between MI and MII)
-> no DNA replication occurs in this stage

Question 6

what are the stages of meiosis? (4)

Answer 6

• P.I -> chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
• M.I -> spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
• A.I -> spindle fires contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
• T.I -> chromosomes decondense, nuclear membrane may reform, ell divides (cytokinesis) to form 2 haploid daughter cells

Question 7

what is MI?

Answer 7

it is a reduction division which homologous chromosomes are separated

Question 8

what is the process of MII? (4)

Answer 8

• P.II -> chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
• M.II -> spindle fibres from opposing centrosomes attach to chromosomes (at centrosomes) and align them along the cell equator
• A.II -> spindle fibres contract and separate the sister chromatids, chromatids/now chromosomes move to opposite poles
• T.II -> chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form 4 haploid daughter cells

Question 9

what is MII?

Answer 9

second division that separates sister chromatids (may not be identical due to crossing in PI)

Question 10

what is the final outcome of meiosis?

Answer 10

the production of 4 haploid daughter cells
- they may all be genetically distinct if crossing over occurs in PI (causing recombination of sister chromatids)

Question 11

what is independent assortment? (3)

Answer 11

• how pairs of alleles separate independently from one another during gamete formation
• one gene/trait is independent to the inheritance of any other gene/trait
• the independent assortment is due to the random orientation of pairs of homologous chromosomes in MI

Question 12

what occurs as a result of the random pairing of homologous chromosomes? (it is not affectd by the orientation of homologous pairs)

Answer 12

• an allele on one chromosome has an equal chance of being paired with or separated from any allele on another chromosome (inheritance is independent of one another)

Question 13

when does synapsis occur?

Answer 13

PI

Question 14

what are the connected homologues called?(2)

Answer 14

bivalent (2 chromosomes)
tetrad (4 chromatids)

Question 15

how are homologous chromosomes connected?

Answer 15

by a protein-RNA complex called syptonemal complex

Question 16

what occurs to autosomes which does not occur to sex chromosomes?

Answer 16

• autosomes always undergo synapsis during meiosis
• sex chromosomes often remain unpaired

Question 17

what may occur to non-sister chromatids while in synapsis? (2)

Answer 17

• non-sister chromatids may break and recombine with their homologous partner (crossing over)
• the non-sister chromatids remain physically connected at these points of exchange regions (chiasmata)

Question 18

what do chiasmata do?

Answer 18

hold homologous chromosomes together as bivalent until anaphase I
- chiasmata formation between non-sister chromatids leads to the exchange of alleles

Question 19

what are chiasmata?

Answer 19

X-shaped point of attachment between 2 non-sister chromatids of a homologous pair

Question 20

what do chiasmata form as a result of?

Answer 20

crossing over
(so, non-sister chromatids should show an exchange of genetic material)

Question 21

what can occur after chiasmata formation between bivalents in PI?

Answer 21

DNA can be exchanged between non-sister homologous chromatids

Question 22

what is crossing over?

Answer 22

the exchange of genetic material
(produces new allele combinations on the chromosome)

Question 23

what are recombinant chromosomes?

Answer 23

chromosomes that consist of genetic material from both homologous chromosomes

Question 24

what does crossing over result in?

Answer 24

new combinations of alleles in haploid cells and increases genetic diversity of potential offspring