Ls 1 Lecture 4- Meiosis Reading

Front 1

homologous chromosomes

Back 1

two chromosomes composing a pair of the same length, centromere position, staining patter, carrying genes controlling the same inherited characters

Front 2

life cycle

Back 2

generation-to-generation sequence of stages in the reproductive history of an organism, from conception to production of its own offspring

Front 3

diploid cell

Back 3

any cell with two chromosome sets

in humans 2n=46

Front 4

haploid cells

Back 4

has single chromosome set

in humans n=23

Front 5

fertilization

Back 5

union of gametes, fusion of nuclei

Front 6

zygote

Back 6

resulting fertilized eggs

Front 7

type of sexual life cycle for humans and most other animals

Back 7

gametes are the only haploid cells
meiosis occurs in germ cells during the production of gametes, which undergo no further cell division prior to fertilization
after fertilization, diploid zygote divides by mitosis, producing multicellular organism

Front 8

type of sexual life cycle for plants and some species of algae

Back 8

"alternation of generations"
includes both diploid and haploid stages that are multicellular
meiosis in sporophyte produces haploid cells called spores
haploid spore doesn't fuse with another cell but divides mitotically, generating gametophyte
cells of gametophyte give rise to gametes by mitosis
fusion of two haploid gametes at fertilization results in a diploid zygote, which develops into the next sporophyte generation

Front 9

sporophyte

Back 9

multicellular diploid stage

Front 10

gametophyte

Back 10

multicellular haploid stage

Front 11

why called "alternation of generations"?

Back 11

sporophyte generation produces a gametophyte as its offspring, the gametophyte generation produces the next sporophyte generation

Front 12

type of sexual life cycle for most fungi and some protists, including some algae

Back 12

after gametes fuse and form a diploid zygote, meiosis occurs without a mutlicellular diploid offspring developing
meiosis produces not gametes but haploid cells that then divide by mitosis and give rise to either unicellular descendants or a haploid multicellular adult organism
subsequently, haploid organism carries out further mitoses, producng the cells that develop into gametes
only diploid stage found in these species is the single-celled zygote

Front 13

sister chromatid cohesion

Back 13

association of sister chromatids

Front 14

sister chromatids

Back 14

two copies of one chromosome, closely associated all along their lengths

Front 15

prophase 1

Back 15

chromosomes begin to condense and homologs loosely pair along their lengths, aligned gene by gene
crossing over is completed while homologs are in synapsis
synapsis ends in mid-prophase and chromosomes in each pair move apart slightly
each homologous pair has one or more chiasmata
centrosome movement, spindle formation, and nuclear envelope breakdown
late prophase 1, microtubules from one pole or the other attach to the two kinetochores

Front 16

crossing over

Back 16

the exchange of corresponding segments of DNA molecules by nonsister chromatids

Front 17

synapsis

Back 17

homologs are held tightly together by proteins along their lengths

Front 18

chiasmata

Back 18

points where crossing over has occured and homologs are still associated due to cohesion between sister chromatids (sister chromatid cohesion)

Front 19

kinetochores

Back 19

protein structures at the centromeres of the two homologs

Front 20

metaphase 1

Back 20

pairs of homologous chromosomes are now arranged on the metaphaase plate, with one chromosome in each pair facing one pole
both chromatids of one homolog are attached to kinetochore microtubules from one pole; those of the other homolog are attached to microtubules of the opposite pole

Front 21

anaphase 1

Back 21

breakdown of proteins responsible for sister chromatid cohesion along chromatid arms allows homologs to separate
homologs move toward opposite poles, guided by the spindle apparatus
sister chromatid cohesion persists at the centromere, causing chromatids to move as a unit toward the same pole

Front 22

telophase 1 and cytokinesis

Back 22

at the beginning of telophase 1, each half of the cell has a complete haploid set of replicated chromosomes, each chromosome is composed of two sister cromatids (one or both chromatids include regions of nonsister chromatid DNA)
cytokinesis usually occurs simultaneously, forming two haploid daughter cells
in some species, chromosomes decondense and the nuclear envelope re-forms

Front 23

cytokinesis

Back 23

division of the cytoplasm

Front 24

in animal cells, during cytokinesis

Back 24

a cleavage furrow forms

Front 25

in plant cells, during cytokinesis

Back 25

a cell plate forms

Front 26

prophase II

Back 26

a spindle apparatus forms
in late prophase II, chromosome move toward the metaphase II plate

Front 27

what are the chromosomes like in prophase II?

Back 27

each still composed of two chromatids associated at the centromere

Front 28

metaphase II

Back 28

the chromoseomes are positioned on the metaphase plate as in mitosis
kinetochores of sister chromatids are attached to microtubules extending from opposite poles

Front 29

are the two sister chromatids of each chromosome identical during metaphase II?

Back 29

no, because of crossing over in meiosis I

Front 30

anaphase II

Back 30

breakdown of proteins holding the sister chromatids together at the centromere allowing chromatids to separate
chromatids move toward opposite poles as individual chromosomes

Front 31

telophase II and cytokinesis

Back 31

nuclei form, chromosomes begin decondensing, cytokinesis occurs

Front 32

each of the four daughter cells from the meiotic division of one parent cell is genetically

Back 32

distinct

Front 33

DNA replication occurs

Back 33

during interphase before mitosis/meiosis I begin

Front 34

number of divisions

Back 34

mitosis: 1
meiosis:2

Front 35

metaphase 1

Back 35

pairs of homologous chromosomes are now arranged on the metaphaase plate, with one chromosome in each pair facing one pole
both chromatids of one homolog are attached to kinetochore microtubules from one pole; those of the other homolog are attached to microtubules of the opposite pole

Front 36

anaphase 1

Back 36

breakdown of proteins responsible for sister chromatid cohesion along chromatid arms allows homologs to separate
homologs move toward opposite poles, guided by the spindle apparatus
sister chromatid cohesion persists at the centromere, causing chromatids to move as a unit toward the same pole

Front 37

telophase 1 and cytokinesis

Back 37

at the beginning of telophase 1, each half of the cell has a complete haploid set of replicated chromosomes, each chromosome is composed of two sister cromatids (one or both chromatids include regions of nonsister chromatid DNA)
cytokinesis usually occurs simultaneously, forming two haploid daughter cells
in some species, chromosomes decondense and the nuclear envelope re-forms

Front 38

cytokinesis

Back 38

division of the cytoplasm

Front 39

in animal cells, during cytokinesis

Back 39

a cleavage furrow forms

Front 40

in plant cells, during cytokinesis

Back 40

a cell plate forms

Front 41

prophase II

Back 41

a spindle apparatus forms
in late prophase II, chromosome move toward the metaphase II plate

Front 42

what are the chromosomes like in prophase II?

Back 42

each still composed of two chromatids associated at the centromere

Front 43

metaphase II

Back 43

the chromoseomes are positioned on the metaphase plate as in mitosis
kinetochores of sister chromatids are attached to microtubules extending from opposite poles

Front 44

are the two sister chromatids of each chromosome identical during metaphase II?

Back 44

no, because of crossing over in meiosis I

Front 45

anaphase II

Back 45

breakdown of proteins holding the sister chromatids together at the centromere allowing chromatids to separate
chromatids move toward opposite poles as individual chromosomes

Front 46

telophase II and cytokinesis

Back 46

nuclei form, chromosomes begin decondensing, cytokinesis occurs

Front 47

each of the four daughter cells from the meiotic division of one parent cell is genetically

Back 47

distinct

Front 48

DNA replication occurs

Back 48

during interphase before mitosis/meiosis I begin

Front 49

number of divisions

Back 49

mitosis: 1
meiosis:2

Front 50

differences between mitosis and meiosis in crossing over/synapsis

Back 50

mitosis has no crossing over, or synapsis

Front 51

differences between mitosis and meiosis in metphase

Back 51

at metaphase I of meiosis, chromosomes ar epositioned on the metaphase plate as pairs of homologs, rather than individual chromosomes, as in metaphase of mitosis

Front 52

differences between mitosis and meiosis during separation of homologs

Back 52

at anaphase I of meiosis, replicated chromosomes of each homologous pair move toward opposite poles, but the sister chromatids of each replicated chromosome remain attached. in anaphase of mitosis, sister chromatids separate

Front 53

shugoshin

Back 53

protects cohesins at the centromere at anaphase I, thus maintaining the attachment between sister chromatids and ensuring they they separate properly during meiosis II

Front 54

reductional division

Back 54

meiosis

Front 55

equational division

Back 55

mitosis