Meiosis

Question 1

Gametes are ____ due to the process of meiosis. Sequence of events is identical for both sexes. ____ of events is dramatically diff

Answer 1

haploid; timing

Question 2

diploid germ cells –> ____gametes and occurs via 2 succesive meiotic div’s without intervening ____ phase. Germ cells are called oogenia or spermatogenia, but as they enter meiosis 1 they are called primary ____ and primary _____

Answer 2

haploid; S; oocyte; spermatocyte

Question 3

What are the genetic consequences of meiosis

Answer 3

1. Reduction of chromosome number (46 diploid to 23 haploid)
2. Segregation of alleles
3. Random assortment of homologs
4. Inc in genetic variation via recombination

Question 4

What is ploidy

Answer 4

origin of an ind chromsomes DNA

Question 5

single parent = \_\_\_\_
both parents = \_\_\_\_
anything else = \_\_\_\_
euploid =\_\_\_\_\_\_
aneuploid = \_\_\_\_\_\_

Answer 5

haploid
diploid
heteroploid
extra full set of chromosomes due to polyspermy
extra single chromosome due to non disjunction

Question 6

N is the total # of DS ___ copies of each chromosome

Answer 6

DNA

Question 7

Interphase somatic cell is _____ and ____ N. Somatic cell after S phase is ____ and ____N which is an intermediate phase. Gamete prior to meiosis II is ____ and ___N which is also an intermediate phase. Our final gamete is ____ and ___N

Answer 7

diploid; 2
diploid; 4
haploid; 2
haploid; 1N

Question 8

What are homologues

Answer 8

identical chromosomes originating from different parents

Question 9

what are sister chromatids

Answer 9

duplicated copy of each chromosome following S phase; conn at centromere

Question 10

What are bivalents/tetrads

Answer 10

pair of duplicated homologues…2 pairs of sister chromatids

Question 11

what is chiasmata

Answer 11

regions where bivalents/tetrads crossover and recombine during prophase 1 of meiosis

Question 12

Female oocytes never complete ____ unless they are fertilized and at that point they are called a ______.

Answer 12

meiosis II (locked in metaphase II); zygote

Question 13

an immature male gamete is called a _____. A mature male gamete is called a _____

Answer 13

spermatid; spermatazoa

Question 14

Males begin meiosis at _____ and generate ____ haploid gametes from one PGC. Female meoisis begins before ______. Meiosis arrests twice, in prophase 1 and metaphase II. We only get ____ haploid from PGC

Answer 14

puberty until death; 4

we are born (in utero); 1

Question 15

The first meiotic division is called ____division and is going from diploid to haploid. While entering meiosis I, cells are diploid & ___N after S phase. Centromeres do not split at ___I. Daughter cells have 1 copy of sister chromatid chromosomes from _____ parent.

Answer 15

reductive; 4; metaphase; single.

Question 16

In mitosis, When sister chromatids line up they go to sep cells so you remain diploid (copies coming from 2 diff parents) so you are ____ and ____N

Answer 16

diploid; 2

Question 17

The diff bet meiosis and mitosis is that:

Answer 17

in meiosis sister chromatids stay together to give you a haploid 2N and then eventually 1N, but in mitosis, sister chromatids sep to give you diploid, 2N

Question 18

What is the longest phase of meiosis?

Answer 18

prophase; where recombination occurs between tetrads.

Question 19

What are the stages of prophase1 in meiosis?

Answer 19

1. Leptotene: chromosomes begin to condense. chromomeres are evident
2. Zygotene: tetrads form bet homologs; this unique to meiosis!
3. Pachytene: homologus recombination occurs; bivalents are evident.
4. Diplotene: bivalents “repel,” chiasmata evident.
5. diakinesis: chromosomes are maximally condensed.

Question 20

Oocytes are arrested at ____stage until ovulation. The prolonged diplotene stage is called _____

Answer 20

diplotene; dictyotene.

Question 21

what is chiasmata impt for

Answer 21

Patients with trisomy’s dont have enough chiasmata forming in their gametes compared to normal people. Chiasmata are impt in keeping tetrads aligned until the right time and rep places where homologous recombination is occuring.

Question 22

crossing over occurs during _____

Answer 22

prophase 1

Question 23

What makes up the synaptonemal complex

Answer 23

1. lateral element

2. central element

Question 24

What is the recombination nodule

Answer 24

huge protein complex. Placement corresponds to regions of chiasmata formation.

Question 25

what happens during metaphase I

Answer 25

1. nuclear membrane disappears
2. spindle forms
3. paired chromosmes align at equatorial plane.
4. centromeres orient toward opp poles.

Question 26

Why don’t sister chromatids sep in meosis 1? *** ask about this slide (18)

Answer 26

Securin is not sep or being ubiquinated and separase does not become active. Not breaking the cohesin thats holding the sister chromatids together in meosis 1. Not being ubiquinated by APC.

Question 27

What happens during anaphase

Answer 27

Where disjunction occurs: tetrads disjoin and sister chromatid pairs are drawn to opp poles of the cell; thus chromosome # is halved. You get indep assort of chromosomes from maternal vs paternal origin. Each chromatid contains segments derived from each parental chromosome pair due to crossing over.

Question 28

What is the most error prone step of meiosis

Answer 28

anaphase 1

Question 29

when does nondisjunction occur

Answer 29

when homologous chromsomes fail to sep during meiosis. Results in some gametes with 24 or 22 chromosomes. Can occur at meiosis I or II. If abormal gametes involved in fertilization you get: monosomy, trisomy or uniparental disomy.

Question 30

how does telophase I or cytokinesis work?

Answer 30

1. Decondensation of chromosomes
2. Reformation of nuclear membrane
3. 2 haploid daughter cells (2N)
4. cells enter a brief interphase
   * cells do not enter S phase prior to next div*

Question 31

Spermatocytes divide their cytoplasm approx equally to yield ____ secondary spermatocytes. Oocytes div. very unevenly to yield ____ secondary oocyte which yields to ___ polar body

Answer 31

2; 1; 1

Question 32

What has all the genetic info that the female egg has?

Answer 32

polar body

Question 33

Meiosis II refers to ____division bc its going from ___N to ___N. Sister chromatids are now separated. The end result is ____haploid secondary spermatocytes, ____ haploid secondary occyte + ____only if egg is fertilized

Answer 33

equational; 2; 1;

4; 1; polar body