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Biology 2311-- Fall 2022 > Chapter 11 > Flashcards

Chapter 11 Flashcards

1
Q

Where does meosis occur?

A

Germ line cells (diploid cells)

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2
Q

What is produced at the end of of meiosis?

A

Gametes (gametogenesis)

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3
Q

What is the ploidy of gametes?

A

Haploid

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4
Q

When is ploidy restored?

A

At fertilization

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5
Q

Why is meosis important?

A

It reduces genetic content

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6
Q

How does meosis create variability?

A

They mix genetic information into new combinations, so none of the offspring are likely to be genetically identical

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7
Q

Meiotic cell cycle

A

Duplicated chromosomes in the parental cell are distributed to four daughter cells, each of which has half the number of chromosomes of the parental cell. DNA replicates, cromosomal proteins duplicated in interphase, and identical sister chromatids formed.

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8
Q

Meiosis I

A

Homologous chromosomes pair and nonsister chromatids physically exchange segments. This produces 2 cells, each with half the diploid number of chromosomes, but with 2 chromatids

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9
Q

Meiosis 2

A

Sister chromatids separate, daughter chromosomes separate into four different cells, each with the haploid number of chromosomes

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10
Q

Synapsis

A

Homologs pair along their length

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11
Q

Homologous recombination

A

Genetic exchange (crossing over) occurs between homologous chromosomes

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12
Q

Reduction division

A

Meiosis involves two successive divisions, with no replication of genetic material between them

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13
Q

How many chromosomes in a human egg or sperm cell?

A

23, one of each pair

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14
Q

What complex aids in synapsis

A

Synaptonemal complex

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15
Q

When does recombination occur?

A

Prophase 1 of meiosis 1- generates diversity and creates chromosomes with new combinations of alleles

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16
Q

What are alleles?

A

The version of each gene present in the members of a homologous pair

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17
Q

What does recombination do?

A

Creates chromosomes with new combinations of alleles for genes A to F

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18
Q

Process of recombination

A
  1. Homologous chromosomes pair. Each sister chromatid consists of a single double-stranded DNA molecule.
  2. Crossing over occurs, resulting in the exchange of segments
  3. At ferst meiotic division, homologous chromosomes separate
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19
Q

Summarize Meiosis 1 and 2

A

Homologous chromosome pair replicates during premiotic interphase, chromosomes pair during prophase 1 of meiosis, crossing over occurs, division occurs twice

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20
Q

Summarize Meiosis 1 and 2

A

Homologous chromosome pair replicates during premiotic interphase, chromosomes pair during prophase 1 of meiosis, crossing over occurs, division occurs twice

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21
Q

First meiotic division

A

Reduction division- results in daughter cells that contain one homolog from each chromosome pair (no DNA replication between meiotic divisions)

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22
Q

Second meiotic division

A

separates sister chromatids for each homologue

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23
Q

Prohphase 1

A

Replicated chromosomes (sister chromatids) fold and condense in the nucleus
Two chromosomes of each homologous pair undergo pairing, forming tetrads, then they exchange segments - shown by thickened spots

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24
Q

Prometaphase 1

A

Nuclear envelope breaks down, spindle enters former nuclear area, two chromosomes of each pair attach to kinetocore microtubules leading to opposite spindle poles, sister chromatids remain attached

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25
Metaphase 1
Terminal chiasmate hold homologous pairs together; spindle microtubules attach to kinetochore proteins on the outside of each centromere Joined pairs of homologs line up on metaphase plate (orientation is random and is equal to 2^n)
26
Independent assortment
Second major source of genetic variability in meiosis- homologs attach differently to the poles
27
Anaphase
Spindle fibers pull whole centromeres towards poles, and chromosomes separate (each chromosome still has 2 sister chromatids)
28
Telophase 1
Chromosomes are segragated into two clusters, nuclear membrane reforms
29
Interkinesis
single spindle disassebles and forms 2 new spindles
30
Meiosis 2
Prophase 2: Chromosomes condense, spindle forms Prometaphase 2: envelope breaks down, spindle enters nucleus, attaches to kinetocore Metaphase 2: spindle microtubules align chromosomes on the metaphase plate Anaphase 2: spindles separate the two chromatids of each chromosome and pull them to opposite poles Telophase 2: chromatids decondense, dissasemble, form four haploid cells
31
Chromosome Segregation Failure
In nondisjunction, the spindle fails to separate the homologous chromosomes or the sister chromatids, so one pole recerives both chromosomes- zygotes have 3 chromosomes instead of two
32
Sex chromosomes
XX (fully homologous) in females and XY (partly homologous) in males, so gamete from female has X chromosome and male has Y chromosome
33
Sources of genetic variability
Crossing over Independent assortment Female/male gametes
34
Dominant phases
Animals- diploid Plants, algae, fungi- alternate fungi and algae- diploid limited to zygote and haploid dominates
35
Sexual reproduction depends on what?
Meiosis
36
What does meiosis produce?
Gametes with half the number of chromosomes present in the somatic cells of a species
37
What happens at fertilization?
The nuclei of an egg and sperm cell fuse and form a zygote
38
Where does meiosis take place in humans?
Gonads (testes and ovaries)
39
The two representatives of each chromosome in a diploid cell constitute a _____
homologous pair (same genes in same order, one from father and one from mother)
40
What are alleles?
Versions of a gene
41
The diploid cells of humans normally have _____ chromosomes
46 (23 pairs) and each individual has a unique combination of alleles in the chromosomes of each homologous pair
42
What does meiosis do?
Separates homologous pairs, reducing the diploid number to the haploid number. Each gamete receives only one member of each homologous pair
43
How many chromosomes in an ovary or sperm cell?
23
44
How many chromosomes in a zygote?
46
45
The meiotic cell cycle produces _____ different daughter cells that are genetically (identical/different) and have _______ the number of parental chromosomes
four, different, half
46
Does mitosis have a premiotic interphase?
Yes, and DNA replicates in this phase
47
Meiosis 1
the division of the meiotic cell cycle in which homologous chromosomes pair and exchange segments, then separate, resulting in two cells with the haploid number of chromosomes and each chromosome containing two chromatids
48
meiosis 2
second division of the meiotic cell cycle in which the sister chromatids in each of the two cells produced by meiosis 1 separate and segregate into different cells, resulting in four cells with the haploid number of chromosomes
49
describe the overall process of meiosis
1. a diploid cell has a homologous pair of chromosomes 2. dna replication occurs, forming sister chromatids 3. chromosome segments of nonsister chromatids may cross over 4. meiosis 1 separates the homologs, so there are 2 new cells with 1 chromosome and 2 sister chromatids 5. meiosis 2 occurs and separates sister chromatids, forming four cells with the haploid number of chromosomes
50
what is interkinesis?
a brief interphase between meiosis 1 and 2
51
T or F: dna is replicated in interkinesis
F
52
Prophase 1
Replicated chromosomes consist of two identical sister chromatids and begin to condense. each chromosome is held together by cohesion proteins synapsis- the two chromosomes of each pair align along their length, forming a four-chromatid tetrad. the paired homologs form form a closely associated synaptonemal complex crossing over- while synapsed, the paired homologs exchange segments, and these crossing over sites further condense. the crossover signts are called crossovers or chiasmata. towards the end, the synaptonemal complex disappears
53
Prometaphase 1
a meiotic spindle has formed nuclear envelope breaks down, and meiotic spindle moves into former nuclear area kinetochore microtubules connect to the chromosomes - both sister chromatids of one homolog attach to microtubules leading to one spindle pole, and both chromatids of the other homolog attach to microtubules leading to the opposite pole nonkinetochore microtubules from the two poles overlap in the middle of the cell but do not attach to chromosomes
54
metaphase 1
kinetochore microtubules align the tetrads in the metaphase plate
55
anaphase 1
enzyme separase cleaves the cohesion rings around the arms of the sister chromtids. the two chromosomes of each homologous pair separate and move to opposite spindle poles, but the chromosomes still exist as sister chromatids
56
telophase
new nuclear envelopes may form
57
interkinesis
no dna replication, microtubules reassemble into two new meiotic spindles for the second division
58
prophase 2
chromosomes condense and a meiotic spindle forms
59
prometaphase 2
nuclear envelope breaks down and kinetochore microtubules attach to the kinetochores of each chromosome
60
metaphase 2
movements of microtubules align the chromosomes on the metaphase plate
61
anaphase 2
separase cleaves the cohesion proteins and microtubules separate the chromatids, moving into opposite poles. at the completion of anaphase 2, the chromatids have been segregated to the two poles
62
telophase 2
the chromosomes begin decondensing, eventually reaching interphase, the meiotic spindles disassemble, and new nuclear envelopes form around the masses of chromatin. cytokinesis typically follows, resulting in four haploid cells with a nucleus containing 1/2 the number of chromosomes present in a nucleus of the same species
63
where did meiosis originate?
eukaryotes
64
how many chromatids are present in meiosis for human cells?
92 at the beginning
65
what is nondisjunction?
both chromosomes of a homologous pair may connect to the same spindle pole, meaning the homologous chromosomes are not separates, so one pole receives both chromosomes and other has no copies of that chromosome. then, when the sister chromatids divide, one cell has 3 chromosomes and the other only has 1
66
nondisjunction in meiosis 2
both sister chromatids connect to a kinetochore microtubule, meaning that one pole receives both sister chromatids, so this produces 1 gamete with 3 chromsomes, 1 with 1 chromosome, and 2 normal ones
67
are x and y partially or fully homologous?
partially
68
what are the three sources of genetic variability?
crossing over between paired homologous chromosomes during prophase 1 independent assortment during anaphase 1 where chromosomes may end up on either side of the cell fetilization- recombines alleles in offspring
69
describe crossing over
homologous chromosomes form tight associations and synapse. each sister chromatid is a single strand of dna and the alleeles for two genes on one chromosome are present. 2. crossing over between the homologous pairs results in the exchanging of sefments 3. after meiosis 2, two daughter cells have parental genes AB and ab and the other two have recombinants Ab and aB
70
how many nuclei receive unchanged vs changed chromatids?
2 unchanged (parental chromosomes), 2 changed from crossing over (recombinant) only occurs between 2 of the 4 chromatids in a homologous pair, but can occur multiple times
71
how many times does crossing over typically occur?
2 or 3 sites in each set of paired chromosomes
72
independent assortment
in prometaphase 1, the homologous pairs of chromosomes attach to the spindles, and for each homologous pair, one chromosome attaches to one side and one attaches to the other and which side the sister chromatids go to is independent
73
fertilization
the chance union of gametes further ampliffies the variability
74
how are identical twins made?
mitotic division of a fertilized egg cell
75
Anima life cycle
diploid phase dominates and meiosis is followed directly by game te fertilization
76
all plants, some fungi, and algae
generations alter between haploid and diploid phases (both multicelular). fertilization produces the diploid sporophytes, which grow to maturity then undergo meiosis to produce haploid spores, which grow into maturity via mitosis into gametophites, and at maturity, some cells in these gametophytes develop into egg or sperm nuclei. fusion of a haploid egg and sperm nucelus produces a diploid zygote nucleus that divides by mitosis to produce the diploid sporophyte generation again. in shrubs, trees, and flowerts, the sporophyte is most visible and the microscopic state is the gametophyte generation. . the female gametophyte is in the flower and the male gametophyte is the pollen, which contacts the stigma of the flower and penetrates the ovule to release a haploid nucleus that fertilizes the haploid of the female, producing a sporophyte.
77
other fungi and algae
mainly haploid, zygote is diploid
78
in female animals, only ___ out of four of the nuclei produced by meiosis becomes an egg cell nucleus
one
79
animals are only haploids as
sperm or eggs

Biology 2311-- Fall 2022 (12 decks)

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