Lecture 45. Meiosis - Shuffling The Genetic Deck

Question 1

What move chromosomes?

Answer 1

Microtubules

Question 2

How long is the DNA in a human cell?

Answer 2

Two metres

Question 3

When can chromosomes be studied?

Answer 3

When they are condensed

Question 4

What is a karyotype?

Answer 4

A catalogue of all the chromosomes in an organism

Question 5

Do plants have sex chromosomes?

Answer 5

Some do

Question 6

What are telomeres?

Answer 6

Found at the ends of the chromosome, they maintain length and have a repeated structure

Question 7

What is the centromere?

Answer 7

Where the spindles attach to the chromosome, satellite DNA

Question 8

What do euchromatin and heterochromatin do in the chromosome?

Answer 8

Package DNA, RNA & protein

Question 9

What are the four structures a chromosome can have?

Answer 9

Telocentric
Acrocentric
Submetacentric
Metacentric

Question 10

What is the short arm of a submetacentric chromosome called?

Answer 10

p

Question 11

What is the long arm of a submetacentric chromosome called?

Answer 11

q

Question 12

What can the visible bands in chromosomes tell you?

Answer 12

High resolution physical map position

Question 13

What are the two types of cell division?

Answer 13

Mitosis and meiosis

Question 14

What are the stages of mitosis?

Answer 14

Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 15

What happens during interphase?

Answer 15

Chromosomes & organelles replicate

Question 16

What happens during prophase?

Answer 16

Spindle begins extending from poles, and attaches to centromeres (kinetochore)

Question 17

What happens during metaphase?

Answer 17

Centromeres align at the equator (metaphase plate) - bipolar attachment

Question 18

What happens during anaphase?

Answer 18

Chromosomes migrate to opposite poles - sister chromatids are now chromosomes

Question 19

What happens during telophase?

Answer 19

Chromosomes at poles, spindle disassembles, nuclear membrane reforms

Question 20

What happens during cytokinesis?

Answer 20

Chromosomes decondense and cells divide

Question 21

What breaks down the cohesin protein between metaphase and anaphase?

Answer 21

Separase

Question 22

What does meiosis result in?

Answer 22

Four genetically distinct cells

Question 23

What occurs in prophase I during meiosis?

Answer 23

Centrosome splits & move to poles DNA condensing begins
Homologous chromosomes align & synaptonemal complex forms
Doublestrand breaks arise & chiasmata form
Nuclear membrane breaks down
Spindle begins to form DNA fully condensed, synaptonemal complex breakdowns, & monopolar kinetochores attach chromosomes to spindle

Question 24

What occurs in metaphase I during meiosis?

Answer 24

Kinetochores have aligned at the equator (metaphase plate)

Question 25

What occurs in anaphase I during meiosis?

Answer 25

Monopolar attachment pulls homologous chromosomes to opposite poles

Question 26

What occurs in telophase I and anaphase I during meiosis?

Answer 26

Haploid cells have formed ‘Shuffling the deck’ has occurred by independent assortment of parental chromosomes and crossing-over of chromosome arms

Question 27

What are the five stages of prophase I?

Answer 27

Leptotene Zygotene Pachytene Diplotene Diakinesis

Question 28

What occurs in leptotene?

Answer 28

Leptotene - 'thin thread' stage Chromosomes start to condense & become visible Homolog pairing begins Double-strand DNA breaks are introduced (potential sites for crossing-over)

Question 29

What occurs in zygotene?

Answer 29

Zygotene - 'paired threads' stage A synaptonemal complex begins to form between homologous pairs (Synapsis) Paired homologs now referred to as bivalents

Question 30

What occurs in pachytene?

Answer 30

Pachytene - 'thick thread' stage Condensing of chromosomes continues Synaptonemal complex is complete Bivalents now have four sister chromatids (tetrads) Crossing-over is completed

Question 31

What occurs in diplotene?

Answer 31

Diplotene - 'two thread' stage Synaptonemal complex disassembles Each pair of sister chromatids begins to separate Chiasmata are visible regions of cross-over between non-sister chromatids

Question 32

What occurs in Diakinesis?

Answer 32

Diakinesis - 'moving apart' stage Chromosomes repel each other Non-sister chromatids remain loosely associated via chiasmata Nuclear membrane and nucleolus disappear Monopolar attachment of chromosomes to spindle fibers

Question 33

What are the functions of the synaptonemal complex?

Answer 33

Facilitates late stages of recombination Prevents different homolog pairs from getting entangled