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Biology - Genetics > Intracellularly - Meiosis > Flashcards

Intracellularly - Meiosis Flashcards

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1
Q

Meiosis

A

This is cell division where a diploid cell splits into four haploid cells in sexual reporduction in eukaryotes.

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2
Q

Synapsis

A

Fusion of chromosome pairs at the start of meiosis

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3
Q

What is the process of meiosis brief?

A

Four strand structure forms where the homologous chromosomes attach
Chromosomes seperate to poles, with cleavage(haploid)
Chromatids seperated into two seperate daughter cells, haploid

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4
Q

Meiocytes

A

A cell differnetiating into a gamete through meisosi

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5
Q

What are the two meiocytes?

A

Oocytes and Spermatocytes

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6
Q

What are the four phases of mieosis?

A

Prophase, metaphase, anaphase, telophase

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7
Q

What are the five stages of prophase?

A

Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis

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8
Q

What happens in leptotene?

A

Chromosomes become visible and threadlike by condensation, with synapsis

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9
Q

What carries out synapsis?

A

Synaptonemal complex

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10
Q

Synaptonemal Complex

A

This holds the two homologous chromosomes together

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11
Q

What happens in Pachytene

A

Crossing over occurs

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12
Q

Homologous Recombination

A

This is the exchange of segments of chromosomes by cross-wise joining across holliday junctions

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13
Q

First step in HR?

A

Introduction of DSBs by Spo11 protein

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14
Q

Why is DSB break important in HR?

A

Allow linkage of the DNA segments and spatial coalignment of the homologs

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15
Q

Second step in HR…

A

Spo11 remains bound after DS cleavage, Exo1 exonuclease resects DNA ends exposed, exposing 3’s tails

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16
Q

Third step in HR…

A

Tails bound by RecA, which catalyze strand invasion into homologous duplex DNA

17
Q

Holliday junction

A

Homologous recombination intermediates, being key sites of genetic recombination.

18
Q

Roles of recombination..

A

Increase genetic diversity, pairs/segregates the homologs

19
Q

What happens in Diplotene

A

Synaptonemal Complex breaks down, and chiasmata begin to seperate

20
Q

Chiasmata

A

Chromatin structures that link homologs together until anaphase

21
Q

What happens in Diakinesis?

A

Chromosomes fully condensed and the homologs repel

22
Q

Metaphase

A

Where the two bivalents, by their homologous chromosomal centromeres, via MT action, orient to opposite poles

23
Q

Where do chromosomes allign in metaphase?

A

Metaphase plate.

24
Q

How is bivalent split in progeny random?

A

Orientation in metaphase plate, which is random, determines which bivalent is found.

25
Q

What are the gametes two heterozygous homologs could form?

A

A B and a b or A b and a B with 1;1;1;1 ratio

26
Q

What is the physical basis of independent assortment?

A

The randomness of allel seperate in metaphase

27
Q

Anaphase

A

Poleward segregation occurs and allele seperate

28
Q

What is the physical basis for Principle of Segregation?

A

Anaphase poleward segregation and allele separation.

29
Q

Srtucture of Synap Complex…

A

Zipper like structure, in prophase 1 the sister chromatids develop axial element, connceted by transever filaments

30
Q

Axial Element

A

An SC structure organising chromatids into DNA loops, with bases anchroed to it.

31
Q

Functional importance of chiasmata?

A

Attachment of the two homologous chromosomes to opposite spindle poles, for segregation in meiosis 1

32
Q

Importance of chiasmata?

A

Efficient homolog disjunction

33
Q

Process of crossover…

A

Spo11 DSB, DNA resection producing a DNA strand with a 3’ end subsequently bound by Rad51
Crossover with invasion of 3’ tail into OTHER homolog, forming the holliday junction.

34
Q

Crossover Interference

A

Describes the non-random placement of crossovers with respect to each other in meiosis.

35
Q

Why does crossover interference occur?

A

Formation of crossover is tension dependent, however crossovers also relieve tension, so crossovers can form only locally.

36
Q

Heterochromatin

A

A chromosome material of increased density than normal, supressing/modifying gene activity.

37
Q

Structure of the holliday junction in crossover….

A

D loop formation with strand invasion, where DNAP extends 3’ end, forming holliday junction by annealing of 3’ end to the D loop

Biology - Genetics (14 decks)

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