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B9- GENETIC DIVERSITY AND ADAPTATION > 9.2- MEIOSIS AND GENETIC VARIATION > Flashcards

9.2- MEIOSIS AND GENETIC VARIATION Flashcards

1
Q

In what ways can cell division occur? (2)

A

mitosis

meiosis

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2
Q

What does mitosis produce?

A

two daughter cells with same number of chromosomes as parent cell as each other

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3
Q

What does meiosis usually produce?

A

four daughter cells, each with half the number of chromosomes as parent cell

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4
Q

What do two gametes do in sexual reproduction?

A

two gametes fuse to give rise to new offspring

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5
Q

What is the diploid number of chromosomes in humans?

A

46

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6
Q

Why must the number of chromosomes be halved at some stage in the cycle?

A

to maintain constant number of chromosomes in adults of species

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7
Q

What does the halving of the number of chromosomes occur due to?

A

meiosis

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8
Q

In most animals when does meiosis occur?

A

in formation of gametes

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9
Q

In some plants i.e. ferns, how are gametes produced?

A

by mitosis

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10
Q

In the fern (type of plant) life cycle, when does meiosis occur?

A

in formation of spores

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11
Q

What does every diploid cell of organism have?

A

two complete sets of chromosomes: one set provided by each parent

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12
Q

What happens to homologous pairs during meiosis?

A

homologous pairs of chromosomes separate, so only one chromosome from each pair enters daughter cell

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13
Q

What is the haploid number of chromosomes in humans?

A

23

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14
Q

What happens when two haploid gametes fuse at fertilisation?

A

diploid number of chromosomes restored

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15
Q

How many nuclear divisions does meiosis involve?

A

two nuclear divisions

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16
Q

What happens in the first division (meiosis 1)?

A

homologous chromosomes pair up + their chromatids wrap around each other
equivalent portions of these chromatids may be exchanged in crossing over

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17
Q

What happens by the end of the first division (meiosis 1)?

A

homologous pairs have separated, with one chromosome from each pair going into one of the two daughter cells

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18
Q

What happens in the second meiotic division (meiosis 2)?

A

chromatids move apart

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19
Q

What happens by the end of the second meiotic division (meiosis 2)?

A

four cells have usually been formed

in humans each of these cells contain 23 chromosomes

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20
Q

What does meiosis produce among the offspring?

A

genetic variation

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21
Q

What can the genetic variation among offspring from meiosis lead to?

A

adaptations that improve survival chances

22
Q

How does meiosis bring about genetic variation? (2)

A

independent segregation of homologous chromosomes

new combinations of maternal + paternal alleles by crossing over

23
Q

What is a gene?

A

length of DNA that codes for polypeptide

24
Q

What is the locus?

A

position of gene on chromosome or DNA molecule

25
Q

What is an allele?

A

one of the different forms of a particular gene

26
Q

What are homologous chromosomes?

A

pair of chromosomes, on maternal + one paternal that have same gene loci

27
Q

What does each chromosome do during meiosis 1?

A

each chromosomes lines up alongside its homologous partner

28
Q

In what way do each chromosome arrange themselves when they line up alongside its homologous partner during meiosis 1?

A

do so at random

29
Q

What happens to each of the homologous pair when they line during meiosis 1?

A

one of each pair will pass to each daughter cell

30
Q

How is where which pair of the homologous pair from meiosis 1 determined?

A

which one of pair goes into daughter cells, and with which one of any of other pairs, depends on how pairs lined up in parent cell

31
Q

Why is the combination of chromosomes of maternal + paternal origin that go into the daughter cell at meiosis 1 a matter of chance?

A

since pairs lined up at random

32
Q

What is the process of the chromosomes lining up in meiosis 1 and being separated called?

A

independent segregation

33
Q

What does each member of a homologous pair of chromosomes have?

A

has exactly the same genes + so determines characteristics

34
Q

What can be different about homologous chormosomes?

A

alleles of genes

35
Q

What does the independent assortment of the homologous chromosomes do?

A

produces new genetic combinations

36
Q

How do the haploid cells fuse at fertilisation?

A

randomly

37
Q

What do the haploid cells fuse to restore at fertilisation?

A

restore diploid state

38
Q

How is variety produced in offspring from gametes?

A

each gamete has different make-up + their random fusion produces variety

39
Q

How is even more variety produced when gametes fuse?

A

gametes come from different parents two different genetic make-ups combined + so even more variety results

40
Q

What happens after the chromosomes line up alongside its homologous partner in meiosis 1?

A

chromatids of each pair become twisted around one another

41
Q

What happens during the process of chromatids of each pair becoming twisted around each other?

A

tensions created + portions of chromatids break off

42
Q

What may happen to the broken portions when chromatids of each pair become twisted around one another and tensions created + portions of chromatids break off?

A

broken portions might then re-join with chromatids of its homologous partner

43
Q

Usually, what is it during crossing over?

A

usually it’s equivalent portions of homologous chromosomes that are exchanged

44
Q

What happens as the chromatids twisted, tensions created + broken portions might rejoin with chromatids of its homologous partner?

A

new genetic combinations of maternal + paternal alleles produced

45
Q

What is the process of chromatids crossing over one another many times known as?

A

crossing over

46
Q

What is the process of broken-off portions of chromatids recombining with another chromatid known as?

A

recombination

47
Q

What does crossing over increase?

A

genetic variety

48
Q

Mathematical calculation to determine number of possible combinations of chromosomes for each daughter cell?

A

2^n

n- number of pairs of homologous chromosomes

49
Q

Mathematical calculation to determine number of possible combinations of chromosomes in offspring produced as result of sexual reproduction?

A

(2^n)^2

n- number of pairs of homologous chromosomes

50
Q

What are the calculations to determine number of possible combinations based on?

A

chromosomes staying intact throughout meiosis

51
Q

In practice from the calculations for number of possible combinations, what do we know?

A

crossing over between chromatids during meiosis I exchanges sections of chromosomes between homologous pairs in process called recombination
as recombination occurs each time gametes made, it will greatly increase number of possible chromosome combinations in gametes

B9- GENETIC DIVERSITY AND ADAPTATION (4 decks)

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