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Biology - AS Level > meiosis > Flashcards

meiosis Flashcards

1
Q

what are the 2 types of mutation

A

gene mutation
chromosme mutation

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2
Q

what are gene mutations

A

change in the sequence of bases on the DNA

ultimately changes AA code and protein

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3
Q

what are chromosome mutations

A

a change in the no of chromosomes or change in the overall structure of a chromosome

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4
Q

what are spontaneous gene mutations

A

random mistakes occurring in DNA replication
no particular cause and occur with low frequency

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5
Q

how can the rate of mutation be increased

A

by exposure to mutagenic agents

radiations- x-rays and UV light
some chemicals eg benzpyrene in tobacco smoke which damages base cystosine
infectious agents eg HPV

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6
Q

what are the 4 types of gene mutation

A

-addition
-deletion
-substitution
-inversion

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7
Q

what is an addition mutation

A

one or more bases are added
thus frameshift and shifts reading frame-diff protein

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8
Q

what is a deletion mutation

A

one or more bases are deleted from sequence
thus frameshift and shift in reading frame - diff protein

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9
Q

what are substituition mutations

A

one nucleotide base or codon is exchanged for another so only triplet is affected
non-frameshift as only affect on triplet coden so not reading frame

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10
Q

what are inversion mutations

A

a base pr a sequence of bases is reversed
non-frameshift

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11
Q

what are the consequences of gene mutations

A

silent mutations - no effect
due to the removal of introns / mini satellite
code is degenerate - one codon for multiple

mis-sense- leads to formation of altered proteins
sequence of bases changed = altered mRNA
altered mRNA can be translated to diff AA seq
may then form protein w altered tertiary struct
causes affect on function

can be beneficial - advantageous characteristics
or harmful as non-functional

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12
Q

nonsense

A

codon changed to STOP codon then translation is ended prematurely and will be non-functional
has a serious affect on cell

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13
Q

what are the chromosome mutations

A

deletion- segment of chromosome is lost - vital genes could be lost
translocation- segment transferred onto another
duplication- section of chromo is transferred onto its homologous counterpart- so now had 2
inversion- large segment of chromo is now reversed

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14
Q

how are the changes in chromo number referred as

A

small-scale losses or small-scale gains

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15
Q

what is gaining a chromo called

A

trisomy eg downs syndrome

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16
Q

what is losing a chromo called

A

monosomy

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17
Q

what is having a complete extra set of chrome called

A

polyploidy - only plants

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18
Q

how many divisions are in meiosis

A

2

19
Q

what are haploid cells

A

half the diploid number with 1 chromosome from each pair - represented a n

20
Q

what are diploid cells

A

full set of chromosomes in pairs- represented as 2n

21
Q

what are the phases of meiosis

A

meiosis 1
pro 1
meta 1
ana 1
tela 1

meiosis 2
pro 2
meta 2
ana 2 tela 2

22
Q

what occurs in prophase 1

A

-DNA condenses and becomes visible as chromosomes
-DNA replication has already occurred so each chromosome consists of two sister chromatids joined together by a centromere
-The chromosomes are arranged side by side in homologous pairs
-A pair of homologous chromosomes is called a bivalent - formed in a process known as synapsis
-As the homologous chromosomes are very close together the crossing over of non-sister chromatids may occur. The point at which the crossing over occurs is called the chiasma (chiasmata; plural)
-In this stage centrioles migrate to opposite poles and the spindle is formed
-The nuclear envelope breaks down and the nucleolus disintegrates
-spindle forms

23
Q

what occurs in metaphase 1

A

-bivalents become arranged on the equator of the spindle

24
Q

what occurs in anaphase 1

A

-one chromosome from each bivalent is pulled toward opposite poles of the spindle
-the centromeres do not divide
-it is important to remember that each bivalent acts independently so each pole receives a mix of mat and pat chromosomes

25
Q

what occurs in telophase 1

A
  • each pole of cell- now a haploid set of chromo, one from each homologous pair
    -chromosomes decondense
  • nucleoli and nuclear membrane reappear
26
Q

what is the role of meiosis 1

A

to produce two haploid cells - in humans -23

27
Q

how does meiosis 1 introduce variation

A

cross-over events
independent/ random assortment

28
Q

what occurs in prophase 2

A
  • chromo condense
  • nucleoli disappear
    -nuclear mem breaks down
    -centrioles migrate towards opposite poles of cell
  • spindle forms
29
Q

what occurs in metaphase 2

A
  • chromosomes line up on the equator of the spindle
30
Q

what occurs in anaphase 2

A

-centromeres split and chromatids are pulled to opposite poles of the cell

31
Q

what occurs in telophase 2

A

-chromatids decondense
-nuclear mem reform
-nucleolus reappear
-spindle breaks down
-centrioles disappear

32
Q

what then occurs after telophase 2

A

cytokinesis then takes place and produces 4 haploid daughter cells

33
Q

what is the significance of meiosis

A

halves no. of chromosomes producing haploid cells
introduces variation

34
Q

what is the role of meiosis

A

to produce non-genetically identical daughter cells
which are known as gametes

35
Q

what is a cross-over event

A

Crossing over is the process by which non-sister chromatids exchange alleles
Process:
-During meiosis I homologous chromosomes (form bivalent) pair up and are in very close proximity to each other
-The non-sister chromatids can cross over and get entangled
-These crossing points are called chiasmata
-As a result of this a section of chromatid from one chromosome may break and rejoin with the chromatid from the other chromosome

this generates large amounts of variation

36
Q

what is independent assortment

A

Independent assortment is the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I

37
Q

how does independent assortment occur

A

homologous chromo pair up and then separate to opposite poles of the cell - each pair acts independently so random mix

38
Q

what does the possible no. of chromo combo equal to

A

The number of possible chromosomal combinations resulting from meiosis is equal to 2^n
n is the number of homologous chromosome pairs

39
Q

what are some differences bwt mitosis and meiosis

A

The Different Outcomes of Mitosis and Meiosis
Number of daughter cells
Mitosis = 2
Meiosis = 4
Ploidy of daughter cells
Mitosis = 2n
Meiosis = n
Are the daughter cells genetically identical to the parent cells and each other?
Mitosis = yes
Meiosis = no - cross over / IA

meiosis - 2 divisions
mitosis - 1 division

meiosis - production of gametes
mitosis - asexual rep and tissue growth + repair

40
Q

how does IA affect fertilisation

A

During fertilisation any male gamete can fuse with any female gamete to form a zygote
This random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a unique combination of alleles
There is an almost zero chance of individual organisms resulting from successive sexual reproduction being genetically identical

41
Q

what is non-disjunction

A

the failure of either chromosomes or chromatids to separate and leads to gamete with abnormal chromo numbers

this can happen in either meiosis 1 or 2

42
Q

how do you determine where meiosis occurs in a life cycle

A

when chromosome number halves
2n - n
NOT WHEN ALWAYS WHEN PRODUCE GAMETES

work out the adult cell in each - will be 2n

43
Q
A

Biology - AS Level (14 decks)

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