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Biology > 3.4.3 - Genetic diversity can arise as a result of mutation or during meiosis > Flashcards

3.4.3 - Genetic diversity can arise as a result of mutation or during meiosis Flashcards

1
Q

how many chromosomes do normal body cells have

A

normal body cells have the diploid number (2n) of chromosomes

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2
Q

what does a cell having a diploid number of chromosomes mean

A

each cell has 2 of each chromosome (a pair), one from mum and one from dad

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3
Q

how are chromosomes that make up each pair similar

A

chromosomes that make up each pair are the same size/have same genes although could have different versions of those genes (alleles)

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4
Q

what are these pairs of matching chromosomes called

A

pairs of matching chromosomes are called homologous pairs

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5
Q

how many homologous pairs do humans have

A

humans have 23 homologous pairs

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6
Q

how many chromosomes do humans have

A

humans have 46 chromosomes in total

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7
Q

what is the diploid number for humans

A

46

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8
Q

what are the gametes in males and females

A

gametes in:
- males = sperm cells
- females = egg cells

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9
Q

how many chromosomes do gametes have

A

gametes have a haploid (n) number of chromosomes

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10
Q

what is the haploid number for humans

A

23

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11
Q

what happens in sexual reproduction

A

in sexual reproduction, 2 gametes join together at fertilisation to form a zygote, which divides and develops into a new organism

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12
Q

fertilisation

A

haploid sperm fuses with haploid egg, making a cell with the normal diploid number of chromosomes (half from dad/sperm, half from mum/egg)

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13
Q

is fertilisation random and why

A

during sexual reproduction, any sperm can fertilise any egg so fertilisation is random

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14
Q

what does random fertilisation produce

A

random fertilisation produces zygotes with different combinations of chromosomes to both parents

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15
Q

what does sexual reproduction increase in a species

A

mixing of genetic material in sexual reproduction increases genetic diversity within a species

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16
Q

what is meiosis a type of

A

meiosis is a type of cell division

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17
Q

where does meiosis take place

A

in the reproductive organs of multicellular, eukaryotic organisms

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18
Q

number of chromosomes in cells before and after meiosis

A

cells that divide by meiosis are diploid to start with, but cells formed from meiosis are haploid (number of chromosomes halves)

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19
Q

what does meiosis in humans/other gametes produce

A

meiosis in humans and other mammals produces gametes directly

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20
Q

what does meiosis in other organisms produce

A

in other organisms (e.g. some insects/plants) it produces haploid cells which later divide by mitosis to become gametes

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21
Q

MEIOSIS
step 1

A
  1. before meiosis starts, the DNA unravels and replicates so there are 2 copies of each chromosome called chromatids
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22
Q

MEIOSIS
step 2

A
  1. DNA condenses to form double-armed chromosomes, each made from 2 sister chromatids. sister chromatids are joined in the middle by a centromere
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23
Q

MEIOSIS
step 3

A
  1. Meiosis I (first division)
    chromosomes arrange themselves into homologous pairs
24
Q

MEIOSIS
step 4

A
  1. these homologous pairs are then separated, halving the chromosome number
25
MEIOSIS step 5
5. meiosis II (second division) pairs of sister chromatids that make up each chromosome are separated (the centromere is divided)
26
MEIOSIS step 6
4. haploid cells that are genetically different from each other are produced
27
what are the 2 main events that happen during meiosis that lead to genetic variation
- crossing over of chromatids - independent segregation of chromosomes
28
CROSSING OVER OF CHROMATIDS part 1
1. in meiosis I, homologous chromosomes come together and pair up.
29
CROSSING OVER OF CHROMATIDS part 2
2. the chromatids twist around each other and bits of chromatids swap over
30
CROSSING OVER OF CHROMATIDS part 3
3. the chromatids still contain the same genes but now have a different combination of alleles
31
CROSSING OVER OF CHROMATIDS what does crossing over in meiosis I mean will happen?
crossing over of chromatids in meiosis I means that each of the 4 daughter cells formed from meiosis II contain chromatids with different alleles
32
INDEPENDENT SEGREGATION OF CHROMOSOMES part 1
1. each homologous pair of chromosomes in your cells is made up of one maternal and one paternal chromosome
33
INDEPENDENT SEGREGATION OF CHROMOSOMES part 2
2. when the homologous pairs are separated in meiosis I, it's completely random which chromosome from each pair ends up in which daughter cell
34
INDEPENDENT SEGREGATION OF CHROMOSOMES part 3
3. so the 4 daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes
35
INDEPENDENT SEGREGATION OF CHROMOSOMES part 4
4. this is called independent segregation of the chromosomes. this 'shuffling' of chromosomes leads to genetic variation in any potential offspring
36
what do gene mutations involve
gene mutations involve a change in the DNA base sequence of chromosomes
37
what are the types of errors that can occur for gene mutation
base deletion and base substitution
38
base substitution
substitution one base is substituted with another
39
base deletion
deletion one base is deleted
40
what does the order of DNA bases in a gene determine
order of DNA bases in a gene determines the order of amino acids in a particular protein
41
what happens if a mutation occurs in a gene
if a mutation occurs in a gene, the sequence of amino acids it codes for (and the protein formed) could be altered
42
EFFECTS OF MUATATION what does the degenerate nature of the genetic code mean
degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet
43
EFFECTS OF MUATATION as genetic code is degenerate, what does this mean about the effects of base substitution
means that not all substitution mutations will result in a change to the amino acid sequence of the protein, some substitutions will still code for the same amino acid
44
do deletion mutations lead to changes in the amino acid sequence
deletion mutations always lead to changes in the amino acid sequence
45
why does base deletion lead to changes in the amino acid sequence
deletion of a base will change the number of bases present, causing a shift in all the base triplets after it
46
are mutations unspontaneous or spontaneous
mutations occur spontaneously e.g. when DNA is misread during replication
47
what do mutagenic agents do
mutagenic agents cause an increase in the rate of mutations/increase probability of a mutation occurring
48
examples of mutagenic agents
- UV radiation - ionising radiation - some chemicals - some viruses
49
what can happen when meiosis goes wrong
cells produced contain variations in the numbers of whole chromosomes or parts of chromosomes - chromosome mutation
50
what are chromosome mutations caused by
errors during meiosis
51
what do chromosome mutations lead to
chromosome mutations lead to inherited conditions as the errors are presents in the gametes
52
give an example of a type of chromosome mutation
chromosome non-disjunction = failure of the chromosomes to sperate properly
53
give an example of something a chromosome non-disjunction can cause
down's syndrome
54
what is down's syndrome caused by
down' syndrome is caused by a person having an extra copy of chromosome 21 (or sometimes an extra copy of part of chromosome 21)
55
how does non-disjunction affect chromosome 21 and hence lead to down's syndrome
non-disjunction means that chromosome 21 fails to separate properly during meiosis, so one cell gets an extra copy of 21 and another gets none
56
what happens when the gamete with the extra copy fuses to another gamete? (down's syndrome)
when the gamete with the extra copy fuses to another gamete at fertilisation, the resulting zygote will have 3 copies of chromosome 21

Biology (17 decks)

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