Lecture 5: Meiosis

Front 1

what happens to chromosomes in meiosis

Back 1

cell division reduces chromosome number by 1/2

Front 2

each daughter cell receives ____ of each homologous chromosome

Back 2

one copy

Front 3

two main purposes of meiosis

Back 3

1. cell division to reduce # of chromosomes by one half

2. crossing over is used to increase genetic diversity of gametes produced

Front 4

crossing over

Back 4

exchange of corresponding DNA segments bw homologous chromosomes

Front 5

in crossing over, it is a _____ exchange

Back 5

equal

Front 6

give overview of meiosis in 3 steps

Back 6

1. homologues pair

2. 1st division: 2n cell divides to give two 1n cells

3. 2nd division: each 1n cell divides to give total of four 1n cells

Front 7

prophase I is subdivided into 5 stages.

name them.

Back 7

1. leptotene

2. zygotene

3. pachytene

4. diplotene

5. diakinesis

Front 8

way to remember 5 subdivisions prophase 1

Back 8

"He lepto over the zygo in pachystan diplo times. Then he diakinesis. He was just a tene."

Front 9

leptotene

Back 9

chromosomes begin to condense

Front 10

zygotene

Back 10

homologous chromosomes begin to pair, synapsis

Front 11

synapsis

Back 11

pairing of homologues

Front 12

what stage does synapsis occur

Back 12

zygotene of prophase I

Front 13

pachytene

Back 13

tetrad or bivalent sometimes visible

Front 14

bivalent

Back 14

pair of synapsed chromosomes

Front 15

tetrad

Back 15

4 chromatids in synapsis

Front 16

diplotene

Back 16

-synapsed chromosomes start to separate

-homologues remain together at chiasmata

Front 17

chaismata

Back 17

apparent point of crossing over

Front 18

diakinesis

Back 18

-homologue segments that are not connected by chiasmata move further apart

-spindle begins to form

-nuclear envelope breaks down

Front 19

metaphase I

Back 19

-bivalents orient at metaphase plate w/ centromeres of homologues on opposite sides of plate

Front 20

anaphase I

Back 20

-chiasmata break down

-homologous chromosomes move to opposite poles

Front 21

telophase I

Back 21

-spindle breaks down

-cell divides (two 1n cells)

Front 22

what are 4 things to remember between meiosis I and meiosis II?

Back 22

1. no DNA replication occurs

2. nuclear envelope may reform transiently

3. chromosomes may decondense briefly

4. meiosis II resembles mitosis, but it starts haploid 1n and sister chromatids are generally not identical bc of crossing over

Front 23

prophase II

Back 23

-spindle begins to form

-if chromosomes decondensed, they recondense

-if nuclear envelope formed, it breaks down

Front 24

metaphase II

Back 24

chromosomes align at metaphase plate

Front 25

anaphase II

Back 25

-centromeres divide and chromatids move to opposite poles

Front 26

telophase II

Back 26

-cytokinesis occurs

-spindle disappears

-nuclear envelope reassembles

Front 27

most important thing to remember about ploidy of meiosis

Back 27

4 haploid (1n) cells, that are not identical

Front 28

meiosis that produces male gametes

Back 28

spermatogenesis

Front 29

3 facts about spermatogenesis

Back 29

1. DNA may "hypercondense"

2. sperm meiosis is relatively brief

3. two of the four 1n gametes may bud from earlier cell as a means of dumping cytoplasm

Front 30

meiosis that produces female gametes

Back 30

oogenesis

Front 31

product of oogenesis

Back 31

oocyte

Front 32

how many oocytes are produced?

what are they composed of?

Back 32

one

a lot of cytoplasm and most stuff needed for early embryonic development

Front 33

what are the other 1n cells called that are not the oocyte?

what do they do/what is their purpose?

Back 33

polar bodies

dump extra chromosomes

Front 34

oocytes can often ____ in an earlier stage

Back 34

arrest, sometimes for decades

Front 35

the polar body many not ______. Doe is in humans?

Back 35

divide

it does not divide in humans

Front 36

which gets majority of the cytoplasm, the polar body or the oocyte?

Back 36

the oocyte

Front 37

mitosis vs. meiosis

1. reduces ploidy

2. # cells produced

3. homologues pair

4. division reducing # of chromosomes by half

5. produces identical daughters

6. produces germ cells

7. produces somatic cells

Back 37

1. meiosis only

2. mit: 2, mei: 3 or 4

3. meiosis only

4. meiosis I

5. mitosis

6. meiosis

7. mitosis

Front 38

principle of segregation

Back 38

hereditary determinants separate in such a way that each gamete is equally likely to inherit either member of the pair

Front 39

oogenesis and stops in what phase

Back 39

late prophase I, between diplotene and diakinesis

Front 40

in humans, meiosis begins...

Back 40

during field development, when fetus is forming

Front 41

meiosis I isn't completed in humans until...

Back 41

ovulation, when period starts and oocyte is ready to ovulate

Front 42

meiosis II isn't completed in humans unless...

Back 42

fertilization occurs

Front 43

in mitosis, daughters are identical unless..

Back 43

mutation or mitotic recombination

Front 44

independent assortment

Back 44

unlinked genes assort independently from one another

Front 45

in independent assortment, what do the products depend on?

Back 45

metaphase I alignment of chromosomes (all outcomes are equally likely)