Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

biology topic 4 > meiosis and genetic variation > Flashcards

meiosis and genetic variation Flashcards

1
Q

what does the process of meiosis produce?

A

Involves two nuclear divisions to create four haploid daughter cells from a single diploid parent cell which are all genetically different from each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what two mechanisms in meiosis cause variation and at what point?

A
  • indépendant segregation of homologous chromosomes
  • crossing over between homologous chromosomes

==> both occur in meiosis 1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is a homologous chromosome?

A

2 chromosomes with exactly the same genes on them but different alleles (maternal and paternal)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is independent segregation?

A

homologous pairs of chromosomes line up opposite each other at the equator of the cell
- it is random which side of the equator the maternal and paternal chromosomes from each homologous pair lie
- the pairs are separated so one of each homologous pair ends up in the daughter cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

how does independent segregation cause variation?

A

the random positioning of the homologous pairs of chromosomes creates a large number of possible chromosomes in the daughter cells produced

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

how do you calculate how many possible combinations there are for which chromosomes end up in the gametes?

A

2^n
where n is the number of homologous pairs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is crossing over?

A

homologous pairs line up opposite each other at the equator and parts of the chromatids can become twisted around each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

explain the process of crossing over in meiosis 1

A
  • when chromaTIDS become twisted around one another, this puts tension on the chromaTIDS and now there is strain which cases parts of the chromatid to break
  • the broken parts of the chromatid recombine with another chromaTID of its homologous pair
  • results in new combinations of alleles in gametes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

compare the processes of meiosis and mitosis

A

1- meiosis is two nuclear divisions whereas mitosis is one

2- meiosis forms haploid cells whereas mitosis forms diploid cells

  • meiosis introduces genetic variation whereas mitosis creates genetically identical cells / clones
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

to identify meiosis in a life cycle diagram, what labelling feature indicates the process of meiosis?

A

meiosis involves a diploid parent cell dividing to become a haploid cell
- diploid is represented as 2n as there are 2 copies of the chromosome pairs whereas haploid is represented as n as there is only one copy

==> the part on the diagram where 2n changes to n is where meiosis occurs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what process further increases genetic variation after the 4 haploid cells have been produced?

A

random fertilisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

how does random fertilisation increase genetic variation further?

A
  • it is random which egg and sperm will fuse in fertilisation as so variation increases further
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

how is the number of possible combinations of chromosomes calculated including random fertilisation?

A

(2^n)^2
- n is the number of chromosome pairs
- all squared for the fusing of 2 gametes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is the definition of genetic diversity?

A

the number of different alleles of genes in a population

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what does genetic diversity enable?

A

a factor enabling natural selection to occur

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is natural selection?

A

the process that leads to evolution in populations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what are the principles of natural selection in the evolution of populations?

A
  • variation due to mutation
  • causes advantageous allele
  • selection pressure means those with the advantageous allele survived and reproduced
  • advantageous allele passed on and increases in frequency in population
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what does natural selection result in?

A

species that are better adapted to their environment
- may be anatomical (structural features such as bird beak shape), physiologic (chemical reactions within the body), or behavioural (how organism behaves to increase survival)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what are the types of selection?

A

directional and stabilising

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is directional selection?

A
  • selection pressure towards one extreme moves the mode in a right or left direction
    – occurs when there is a change in the environment
    – the modal trait changes

eg: antibiotic resistance and peppered moths

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is stabilising selection?

A
  • the modal traits has the selective advantage
  • the modal trait remains the same
  • occurs when there is no change in the environment
    ==> extremes are lost and eliminated which causes the standard deviation to decrease as individuals with the extreme trait decrease

eg: human birth weight

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

define speciation

A

the formation of a new species when changes take place due to natural selection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

when does speciation occur?

A

when members of the same species become geographically isolated and so cannot breed together
==> for example because of flooding, valleys, eathquake formation of islands, mountains

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

how does speciation result in two populations of the same species being unable to interbreed?

A

because they are geographically isolated, there is an accumulation of differences in their gene pools due to the different directional selection pressure on each side of the barrier.
- overtime their alleles become so different that the two populations would be unable to interbreed to make fertile offspring and are therefore classed as two different species

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
what process causes chromosome mutations?
chromosome non-disjunction during meiosis
26
what is non-disjunction?
the chromosomes or chromatids do not split equally during anaphase
27
how do chromosome mutations occur?
spontaneously due to non-disjunction
28
what are the two forms of chromosome non-disjunction?
1. polyploidy - changes in whole sets of chromosomes 2. aneuploidy - changes in the number of individual chromosomes
29
what is formed when polyploidy occurs?
a change in the whole sets of chromosomes so a whole additional set of chromosomes is formed so creates a triploid gamete instead of diploid
30
what is formed when aneuploidy occurs?
a haploid gamete is still produced but one additional or one two few chromosomes are produced
31
what does polyploidy mostly occur in?
plants
32
explain how polyploidy impacts meiosis 1
1- each homologous pair is doubled due to DNA replication in interphase 2- non-disjunction in meiosis 1 where ALL chromosomes pair to separate equally so only one out of two daughter cells created 3- normal division in meiosis 2 where the chromatids separate equally except for in the cell where no chromosomes were 4. however, now 2 diploid gametes have been formed rather than 4 haploid gametes
33
what would happen if a diploid gamete fused with a haploid gamete?
a triploid zygote has been formed (3n) - in the case of humans, it wouldn't survive and form a foetus
34
explain how polyploidy affects meiosis 2
1- each homologous pair is doubled due ti DNA replication in interphase 2- normal division in meiosis 1 where chromosomes separate equally 3- non disjunction in meiosis 2 causes all chromatids to fail to equally separate 4- still forms two haploid and one diploid gamete
35
what does aneuploidy result in and how?
non disjunction occurs which is when individual homologous chromosome pairs fail to separate during meiosis and results in a gamete having one more or one fewer chromosome ==> for example this causes Down's syndrome when there is an extra copy of chromosome 21
36
explain how aneuploidy affects meiosis 1?
- each homologous pair is doubled due to DNA replication in interphase - non-disjunction occurs in meiosis 1 where one chromosome doesn't separate equally - normal division in meiosis 2 where chromatids separate equally - however now, some haploid gametes have one too few (n-1) and the other have one too many (n+1)
37
what happens in fertilisation of a normal gamete and an aneuploidy gamete?
the resultant zygote will have more or fewer chromosomes ===> forms a diploid cell 2n+1 or 2n-1
38
how does aneuploidy affect the formation of haploid cells in meiosis 2?
- each homologous pair is doubled due to DNA replication in interphase - normal division in meiosis 1 - non disjunction occurs in meiosis 2 where one chromatid fails to separate equally ==> results in 2 haploid gamete n-1 and n+1 and two normal haploid gametes (n)
39
what is the definition for a gene mutation?
a change in the sequence of bases in a gene that can alter the sequence of amino acids in a protein
40
what is the frequency of gene mutations occurring?
they occur spontaneously and is random - but the frequency can be increased by mutagenic agents such has carcinogens
41
when are gene mutations likely to occur?
during DNA replication (interphase in the cell cycle)
42
how do gene mutations form a non-functioning protein?
because the gene is altered, it can result in a different amino acid sequence (primary) in the encoded polypeptide. - if this changes, the formation of hydrogen and ionic bonds within the tertiary structure will be in different places and so fold differently. Thus, resulting in a different 3D shape and therefore a non-functioning protein.
43
what are the 6 different types of gene mutations?
addition deletion substitution inversion duplication translocation
44
what is an addition mutation?
when one extra base (DNA nucleotide) is added to sequence
45
what is the impact of addition mutation in the sequence?
- a frame shift occurs which is when all the subsequent codons are altered
46
how does addition mutations cause a non-functioning protein?
This type of mutations can be very harmful because all the altered codons could code for a different amino acid which results in a very different sequence of amino acids in the polypeptide chain and thus the protein will have a completely different shape (tertiary) forming a non-functioning protein
47
what is a deletion mutation?
the deletion of a base in a sequence
48
what is the impact of a deletion mutation in the sequence?
causes a frame shift to the left - all bases move back one because of the deleted base
49
how does a deletion mutation cause a non-functioning protein?
every subsequent triplet / codon is altered and therefore code for a different polypeptide so the primary structure is altered and thus the protein will have a completely different shape (tertiary) forming a non-functioning protein
50
what is a substitution mutation?
one base is changed for a different base but the number of bases remain the same and there is no frame shift.
51
what is the impact of a substitution mutation
only one codon changes so often there is no impact - the genetic code is degenerate so may still code for the same amino acid (no impact)
52
what can a substitution mutation result in?
nonsense mutation mis-sense mutation silent mutation
53
what is a silent mutation?
the substituted bases still codes for the same amino acid because of the degenerate nature of the genetic code
54
what is a mis-sense mutation
different amino aid is coded for in the polypeptide chain - may have no impact - may change the positioning of bonds in the tertiary structure and forming a different shape and not functioning
55
what is a nonsense mutation?
creates a premature stop codon - signal for the cell to stop translation of the mRNA molecule into an amino acid sequence This causes the polypeptide chain produced to be incomplete and this affecting the final protein structure and function
56
what is an inversion mutation?
a section of basses detach from the DNA sequence, but when they re-join they are inverted, so this section of code is back to front ==> example TTC AGG becomes GGA CTT
57
what does an inversion mutation result in?
different amino acids being coded for in a specific region ==> frequently results in a non-functional protein or an entirely different protein produced
58
what is translocation mutation?
a section of bases on one chromosome detaches and attaches onto a different chromosome
59
what impact do translocation mutations have?
can cause significant impacts on gene expression and therefore the resulting phenotype (because a whole section of a chromosome is likely to be multiple genes and therefore lots of proteins will be incorrect for that cell) ==> forms non-functional proteins
60
what is a duplication mutation?
a whole gene or section of a gene is duplicated so that two copies appear on the same chromosome

biology topic 4 (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions