Intracellularly - Meiosis

Question 1

Meiosis

Answer 1

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

Question 2

Synapsis

Answer 2

Fusion of chromosome pairs at the start of meiosis

Question 3

What is the process of meiosis brief?

Answer 3

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

Question 4

Meiocytes

Answer 4

A cell differnetiating into a gamete through meisosi

Question 5

What are the two meiocytes?

Answer 5

Oocytes and Spermatocytes

Question 6

What are the four phases of mieosis?

Answer 6

Prophase, metaphase, anaphase, telophase

Question 7

What are the five stages of prophase?

Answer 7

Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis

Question 8

What happens in leptotene?

Answer 8

Chromosomes become visible and threadlike by condensation, with synapsis

Question 9

What carries out synapsis?

Answer 9

Synaptonemal complex

Question 10

Synaptonemal Complex

Answer 10

This holds the two homologous chromosomes together

Question 11

What happens in Pachytene

Answer 11

Crossing over occurs

Question 12

Homologous Recombination

Answer 12

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

Question 13

First step in HR?

Answer 13

Introduction of DSBs by Spo11 protein

Question 14

Why is DSB break important in HR?

Answer 14

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

Question 15

Second step in HR…

Answer 15

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

Question 16

Third step in HR…

Answer 16

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

Question 17

Holliday junction

Answer 17

Homologous recombination intermediates, being key sites of genetic recombination.

Question 18

Roles of recombination..

Answer 18

Increase genetic diversity, pairs/segregates the homologs

Question 19

What happens in Diplotene

Answer 19

Synaptonemal Complex breaks down, and chiasmata begin to seperate

Question 20

Chiasmata

Answer 20

Chromatin structures that link homologs together until anaphase

Question 21

What happens in Diakinesis?

Answer 21

Chromosomes fully condensed and the homologs repel

Question 22

Metaphase

Answer 22

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

Question 23

Where do chromosomes allign in metaphase?

Answer 23

Metaphase plate.

Question 24

How is bivalent split in progeny random?

Answer 24

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

Question 25

What are the gametes two heterozygous homologs could form?

Answer 25

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

Question 26

What is the physical basis of independent assortment?

Answer 26

The randomness of allel seperate in metaphase

Question 27

Anaphase

Answer 27

Poleward segregation occurs and allele seperate

Question 28

What is the physical basis for Principle of Segregation?

Answer 28

Anaphase poleward segregation and allele separation.

Question 29

Srtucture of Synap Complex...

Answer 29

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

Question 30

Axial Element

Answer 30

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

Question 31

Functional importance of chiasmata?

Answer 31

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

Question 32

Importance of chiasmata?

Answer 32

Efficient homolog disjunction

Question 33

Process of crossover...

Answer 33

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.

Question 34

Crossover Interference

Answer 34

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

Question 35

Why does crossover interference occur?

Answer 35

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

Question 36

Heterochromatin

Answer 36

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

Question 37

Structure of the holliday junction in crossover....

Answer 37

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