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Human Genomics & Genetics > GAG WK4 > Flashcards

GAG WK4 Flashcards

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Biology 101 flashcards
1
Q

What is meiosis

A

cell divides twice to produce 4 cell containing half of the original amount of genetic information

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2
Q

How many gamete cells form from meiosis

A

4 daughter cells

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3
Q

What are homologues

A

any pair of homologous chromosomes

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4
Q

Explain what is meant by meiosis is reductional

A

meiosis reduces the chromosome number by half

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5
Q

Explain what is meant by mitosis is proliferative

A

mitosis maintains the chromosome number

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6
Q

What is the difference between diploid and haploid cells

A

diploid = cells w/ 2 sets of chromosomes
haploid = cells w/ 1 set of chromosomes

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7
Q

What are the features of mitosis

A
  • produces 2 diploid daughter cells
  • no homologous pairing
  • maintains the same number of chromosomes
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8
Q

What are the features of meiosis

A
  • produces 4 haploid daughter cells
  • 2 rounds of cell division
  • reduces the amount of chromosomes
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9
Q

What is the main difference between meiosis I and meiosis II

A

meiosis I = homolgous pair up and separate
meisois II = sister chromatids separate

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10
Q

What are telomeres

A

protective ends of chromosomes

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11
Q

What are centromeres

A

region where sister chromatids are attached

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12
Q

What are microtubules

A

protein structures that pull chromosomes apart

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13
Q

What are kinetochores

A

protein complex on the centromere where microtubules attach

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14
Q

What is the main reason why proper chromosome segregation is important

A

it prevents abnormal chromosome numbers

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15
Q

List the processes necessary for correct chromosome segregation

A
  • chromosome pairing (synapsis)
  • crossing-over
  • spindle fibre attachment
  • checkpoint mechanisms
  • cohesion degradation
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16
Q

Outline the importance of chromosome pairing (synapsis) in chromosome segregation

A

Proper pairing ensures each gamete gets one chromosome from each pair, preventing aneuploidy (ex: Down syndrome)

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17
Q

Outline the importance of crossing-over in chromosome segregation

A

it ensures chromosomes stay together until properly aligned and separated

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18
Q

Outline the importance of spindle fibre attachment in chromosome segregation

A
  • microtubules must attach to kinetochores on chromosomes to pull them to opposite poles
  • errors in attachment can lead to mis-segregation and non-disjunction
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19
Q

Outline the importance of checkpoint mechanisms in chromosome segregation

A
  • Prevents Premature Separation (delays anaphase until all chromosomes are aligned properly)
  • detects errors (misaligned chromosomes are detected)
  • reduces risk of aneuploidy
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20
Q

Outline the importance of cohesin degradation in chromosome segregation

A

cohesin must degrade to allow chromatids to separate

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21
Q

What is the law of segregation

A
  • each parent carries 2 alleles for a gene
  • alleles segregate during meiosis
  • ensures each gamete only gets 1 allele
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22
Q

Outline the law of independent assortment

A
  • genes for different traits on different chromosomes are inherent independently
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23
Q

Outline linkage

A

2 genes on the same chromosomes can be inherited together (unless separated by crossing over)

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24
Q

What increases the odds of linkage

A

if the genes are sitting close to each other

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25
Q

What are the assumptions of Hardy-Weinberg equilibrium

A
  • random mating (no mating preference)
  • no selection (no trait gives an advantage)
  • no mutation + genetic drift + meiotic drive (random segregation of chromosomes)
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26
Q

What is the Hardy-Weinberg equilibrium

A

A principle stating that allele and genotype frequencies in a population remain constant from generation to generation, under certain conditions

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27
Q

What is the purpose of the Hardy-Weinberg equilibrium

A
  • Acts as a baseline to detect evolutionary changes.
  • Helps estimate allele frequencies in populations.
  • Useful in predicting carrier frequencies of genetic disorders
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28
Q

What are unliked genes

A

genes that are inherited independently from each other

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29
Q

What is a genotype

A

specific combination of alleles an individual inherits

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30
Q

What is a phenotype

A

observable trait resulting from that genotype

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31
Q

What is Rec8

A

specific cohesin protein that holds sister chromatids together during meiosis

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32
Q

What is the purpose of cohesin

A
  • ensures sister chromatids remain attached until the right time in cell division
  • preventing premature separation
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33
Q

What is Mps3

A
  • a protein that marks telomeres at nuclear periphery
  • this marking helps facilitate the pairing of homologous chromosomes
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34
Q

Explain the importance of dynamic movement of chromosomes during meiosis

A

-it is necessary for formation of side to synaptonemal complexes, which help hold homologous chromosomes together and promote recombination

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35
Q

What happens when chromosome movement during meiosis is disrupted?

A

It causes errors in chromosomes segregation

36
Q

Why do chromosomes undergo structural changes?

A

It allows them to come closer together, making it easier for homologous chromosomes to align

37
Q

What is the bouquet formation in chromosome pairing?

A

When Telomeres cluster at one side of the nucleus

38
Q

What is the purpose of a bouquet shape during chromosome pairing?

A

It helps bring homologous chromosomes near each other

39
Q

What is the Rabl configuration?

A

The central mirrors are positioned on one side of the nucleus with chromosome arms extending to the opposite side

40
Q

What is the purpose of the Rabl configuration in chromosome pairing?

A

It maintains approximately of the homologous chromosomes

41
Q

How does homologous recombination contribute to chromosome pairing?

A

Homologous recombination uses DNA sequence, similarity between homologs to promote pairing and enable genetic material exchange

42
Q

Why are pairing centers important in chromosome pairing?

A
  • initiate the pairing of homologous chromosomes
  • stabilises the association between homologues
43
Q

What is the synaptonemal complex

A

Protein structure that forms homologous chromosomes

44
Q

What is the function of synaptonemal complex

A

Stabilises the pairing and facilitates genetic recombination

45
Q

Outline prophase I stages

A
  1. thin ribbon
  2. paired ribbon
  3. thick ribbon
  4. double ribbon
46
Q

What happens during the thin ribbon stage

A

Initial pairing begins

47
Q

What happens during the paired ribbon stage

A

Paired Ribbon: The synaptonemal complex forms.

48
Q

What happens during the thick ribbon stage

A

Thick Ribbon: Chromosomes are fully paired and organised.

49
Q

What happens during the double ribbon stage

A

final arrangement before segregation

50
Q

What is the function of enzyme spo11

A
  • creates double-strand breaks in DNA
  • initiates homologous recombination
51
Q

How does Spo11 help chromosome pairing **

A
  • double-strand breaks are repaired using sequences from homologous chromosomes
  • ensures correct pairing
52
Q

What is SMC3

A

protein part of a complex called cohesin

53
Q

What is the function of SMC3

A
  • holds sister chromatids together
  • helps maintain structure of paired homologous chromosomes
54
Q

Why is chiasma formation important in the segregation of homologous chromosomes

A
  • chiasma helps stabilise the chromosomes during segregation
  • ensures homologous pairs stay connected until pulled apart
55
Q

How do microtubules help segregation of homologous chromosomes

A
  • microtubules pull homologous chromosomes toward opposite side of the cell
  • chiasma and cohesin help resist these pulling forces until the right moment
56
Q

What is the chiasmata

A

physical links between homologous chromosomes due to crossovers during prophase I

57
Q

What is the function of chiasmata

A

counteract the pulling forces exerted by microtubules during chromosome segregation

58
Q

What is the link between chiasmata and crossovers

A
  • The number of chiasmata indicates how often crossovers occur
  • If there are fewer chiasmata (therefore fewer crossovers) = a higher chance chromosomes won’t be distributed correctly
  • leads to missegregation
59
Q

What is mono-orientation

A
  • each kinetochore attached to microtubules from only 1 pole
  • use of monopolin protein complex at kinetochore
60
Q

why is that sister kinetochore must exhibit mono-orientation

A

for correct separation of homologous chromosomes

61
Q

What happens to cohesion during anaphase I

A
  • cohesion on chromosome arms is removed
  • allows sister chromatids to separate whilst keep centromeric cohesion intact
62
Q

What happens to cohesion during anaphase II

A
  • centromeric cohesion is removed
  • allows complete separation of sister chromatids
63
Q

What is the role of rec8

A
  • ensures homologous chromosomes stay connected while the arm cohesion is lost
64
Q

What is the role of separase

A
  • a protease that cleaves the Rec8 subunit of cohesion
  • allows chromatids to separate when cell is diving
65
Q

How is separase kept inactive

A
  • securin is a protein that binds to separate and keeps it inactive
  • so the chromatids don’t separate too early
66
Q

How is separase activated

A
  • securin is degraded when all chromosomes are aligned during metaphase
  • ensures separate can now cleave Rec8
  • only when the cell is ready to move to anaphase
67
Q

Why is it that at anaphase I, centromeric cohesion is kept phosphorylated by Sgo1-PP2A

A

preventing premature separation of sister chromatids during meiosis I

68
Q

What is meiotic recombination

A

homologous chromosomes exchange genetic material

69
Q

What are the functions of meiotic recombination

A
  • promotes homologous pairing
  • chiasma formation
  • genetic diversity
70
Q

What are meiotic recombination hotspots

A

thousands of hotspots where recombination is more likely to occur

71
Q

How does Spo11 promote DNA breaks

A

it alters the shape of DNA substrates

72
Q

Where does Spo11 activity happen the most

A

meiotic hotspots

73
Q

What are the features of meiotic recombination hotspots

A
  • over 200 DNA breaks per cell
  • distributed across genome but in a non-random manner
  • thousands of hotspots exist where recombination is more likely
74
Q

What are hotspots influenced by

A
  • methylation marks
  • intergenic regions = non-coding areas between genes can affect hotspot designation
75
Q

What is PRDM9

A

gene that determines hotspot specificity and it can turn Spo11 into a site-specific nuclease

76
Q

What is PRDM9 function

A

it directs Spo11 to break DNA at certain spots determining where recombination happens

77
Q

Why are recombination patterns in terms of reproduction

A
  • 2 populations w/ different PRMD9 alleles cannot interbreed
  • they have incompatible recombination patterns
78
Q

What is being activated during DNA damage (DNA breaks)

A

ATM and ATR are activated (kinases)

79
Q

What happens if ATM and ATR become mutated

A

they can lead to defects in DNA repair and meiotic progression

80
Q

Outline how ATM and ATR are activated

A
  1. phosphorylation of chromatin
  2. transient meiotic arrest for DNA repair
  3. Promotion of DNA repair mechanisms to resolve breaks and maintain genomic integrity
81
Q

What happens when Spo11 is knocked out in mice?

A
  • mouse becomes infertile
  • Chromosomes are unable to pair correctly because there are no DNA breaks for recombination
  • Without recombination, no chiasmata are formed
  • cell undergoes apoptosis or produces defective gametes, causing infertility
82
Q

What is Rad51

A

Rad51 is a protein that helps chromosomes pair up by promoting recombination.

83
Q

What is the role of Rad51 in meiosis?

A

It repairs many DNA breaks, but only a few crossovers occur

84
Q

How many crossovers do most chromosomes experience?

A

Most chromosomes experience 1 crossover

85
Q

How are crossovers regulated during meiosis?

A
  • Crossovers happen in specific locations
  • crossover in one area of the chromosome can prevent crossovers nearby
  • helps ensure that crossovers are spaced out properly to prevent too many in one region

Human Genomics & Genetics (7 decks)

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