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2.1.6 cell division, cell diversity and cellular organisation > meiosis > Flashcards

meiosis Flashcards

(50 cards)

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1
Q

what is meiosis

A

type of nuclear division that results in the formation of cells containing half the number of chromosomes in the parent cell

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2
Q

how many chromosomes do normal cells have

A

two chromsomes of each type - one inherited from each parent

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3
Q

what does diploid mean

A

the presense of two complete sets of chromosomes in an organisms cells with each parent contributing a chromosome to each pair

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4
Q

what happens during sexual reproduction

A

two gametes fuse to form a zygote

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5
Q

what is the difference between a gamete and a zygote

A

gametes are sex cells (ovum and sperm) and zygotes are fertilised eggs. they are the origin of all the cells the organism develops

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6
Q

how many chromosomes must gametes contain

A

1/2 the diploid number of chromosomes

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7
Q

why must chromosomes contain 1/2 the diploid number of chromosomes

A

the diploid number = 46 so gametes must have 23 chromosomes otherwise the chromosome number of an organism would double with each round of reproduction

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8
Q

how are gametes formed

A

by meiosis. gametes are genetically unique

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9
Q

how does meiosis work

A

the nucleus divides to form four daughter cells - the gametes. each gamete contains 1/2 the number of chromosomes of the parent cell - it is haploid

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10
Q

what does haploid mean

A

has only one set of chromosomes

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11
Q

what type of division is meiosis

A

a reduction division

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12
Q

what does sexual reproduce increase

A

genetic variation because it involves the combining of genetic material from two (usually) unrelated individuals of the same species by the process of fertilisation

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13
Q

why is genetic variation important

A

genetic variation within a population ensures a species survival when the environment changes as some individuals will have characteristics that enable them to be better adapted to change

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14
Q

why must gametes be haploid

A

so they can fuse together during fertilisation to form a diploid zygote restoring the normal chromosome number

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15
Q

where does meiosis occur

A

occurs in ovaries and testes. the diploid cells in these organs have been in interphase before they enter meiosis

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16
Q

how many chromosomes do human somatic cells contain

A

46 or 23 pairs of homologous chromosomes

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17
Q

what is special about homologous chromosomes

A

they have matching chromosomes containing the same genes at the same loci (plates). they may contain different alleles for some of the genes

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18
Q

where do the chromosomes in each pair come from

A

from each parent - one maternal and one paternal

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19
Q

what does each nucleus of an organisms cells contain

A

two full sets of genes, a pair of genes for each characteristics

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20
Q

what is an allele

A

different versions of the same gene

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21
Q

what will all different alleles have

Study These Flashcards
A

different alleles of a gene will all have the same locus (same position on a particular chromosome)

22
Q

why will homologous chromosomes be the same size and length when they are visible in prophase

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A

they have the same genes in the same positions

23
Q

what happens in meiosis I

Study These Flashcards
A

the 1st division in the reduction division when the pair of chromosomes are separated into two cells. each cell will contain one full set of genes instead of two so the cells are haploid

24
Q

what happens in meiosis II

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A

the 2nd division is similar to mitosis and the pairs of chromatids present in each daughter cell are separated, forming two more cells. four haploid daughter cells are produced in total - four haploid gametes

25
how does meiosis produce genetic variation
homologous pairs of chromosomes swap parts of their genetic material. this is crossing over chromosomes from each pair are randomly allotted to daughter cells by independant assortment
26
when does crossing over happen
prophase I
27
when does independant assortment happen
in anaphase I it leads to random distribution of maternal and paternal chromosomes in anaphase II it leads to further random distribution of genetic material
28
what is a chromosome
threadlike structure of nucleic acids and protein (histone) found in the nucleus of most living cells carrying genetic information in the form og chromosomes
29
what are homologous chromosomes
two chromosomes in a pair, one maternal and one paternal. pairing happens at meiosis and having the same structural features and patterns of genes. one homolog from each parent
30
what is a bivalent
a pair of homologous chromosomes in synapsis during meiosis
31
what does tetrad mean
another word for bivalent - a pair of homologus chromosomes that have been synapsed
32
what does synapsis mean
the fusion of chromosome pairs at the start of meiosis. this is when genetic material is exchanged
33
what is chromatin
the material of which the chromosomes of organisms other than bacteria (i.e. eukaryotes) are composed of consisting of histone protein, RNA and DNA
34
what is a chromatid
each of the two threadlike strands into which a chromosome divides longitudinally during cell division. each contains a double helix of DNA
35
what is independant assortment
occurs when homologous pairs are separated into daughter cells during meiosis. the chance of one chromosome being separated into a daughter cell is independant of any other chromosomes
36
what is crossing over
the exchange of DNA between paired homologous chromosomes that occurs during meiosis
37
what is meiosis preceded by
DNA synthesis. each chromosome is double stranded and checked for errors before nuclear division begins
38
what are the stages of meiois I
prophase I metaphase I anaphase I telophase I
39
what are the stages of meiois II
prophase II metaphase II anaphase II telophase II
40
what happens in prophase I
- chromatin condenses - nuclear envelope disintegrates - spindle fibres begin to form - homologous chromosomes pair up forming bivalents - crossing over occurs = exchange of genetic material between non sister chromatids
41
what happens in metaphase I
- chromosomes align on the equator - spindle fibres attach to the centromeres - independant assortment - position of each bivalent is independant of all the other chromosomes - maternal and paternal chromosomes can be seen on either side of the equator
42
what happens in anaphase I
- homologous chromosomes are pulled by the spindle fibres to the poles - not pulled apart (i.e the homologs) - causes genetic variation
43
what happens in telophase I
- nuclear envelope reforms - chromosomes uncoil - cells undergo cytokinesis - cells are now haploid cells (two unique chromatids - chromosomes are still bivalents
44
what happens in prophase II
- beginning of 2nd division - chromosomes recondense - nuclear envelope breaks down again - spindle fibres reform
45
what happens in metaphase II
- chromosomes are aligned on the equator by spindle fibres - independant assortment occurs again - more genetic variation is caused
46
what happens in anaphase II
- chromatids are split apart by spindle fibres - chromatids move to the poles of the cells (same as anaphase in mitosis)
47
what happens in telophase II
- nuclear envelope reforms - cytokinesis occurs - uniques gametes have been formed 4 unique gametes have formed - chromatids have been separated
48
describe crossing over in detail
in synapsis chromosomes pair and form a bivalent. homologous chromosomes are held at points called chiasmata. cross over between non sister chromatid occur at the chiasmata. results in new gene combinations forming on chromatids (recombination). once chiasmata are formed, homologous chromosomes condense as bivalents and separated in meiosis.
49
what happens if crossing over occurs
all 4 haploid cells are genetically unique
50
what happens in independant assortment
position of chromosome in metaphase shows which daughter cell the chromosome segregates to. separation of alleles occur during gamete formation so they contain one allele of each pair. the chromosomes move randomly to opposite poles

2.1.6 cell division, cell diversity and cellular organisation (6 decks)

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