Meiosis

Question 1

Amount of DNA at each division in meiosis

Answer 1

Meiosis I reduces 4c to 2c

meiosis reduces 2c to 1c

Question 2

describe the 5 stages of prophase I

Answer 2

Leptotene (Greek meaning - narrow threads; referring to chromosomes condensing to form string of beads; separate sister chromatids not yet visible)

zygotene (synapsis of homologous chromosomes ; pair is called a bivalent)

pachytene (chromatid pairs begin to separate; crossing over occurs)

diplotene (homologous chromosomes fully separate into 2 pairs of chromatids held only by chiasma)

diakinesis (terminalisation of chiasma, nucleoli/nuclear envelope disappear, centrioles begin to make spindle; chromosomes fully condensed - all 4 chromatids visible )

Question 3

Metaphase 1

Answer 3

bivalents align across the cell equator

Question 4

Anaphase 1

Answer 4

Chromosomes pairs separate and chromosomes move to opp ends of cell

Question 5

Telophase I

Answer 5

Each daughter cell has 2n chromosomes

nuclear envelope may reassemble before or prophase II

Question 6

Meiosis II

Answer 6

Centromeres split at the kinetochores

sister chromatids pulled to opp poles

tetras of haploid cells formed

Question 7

At which stages of meiosis is genetic variation introduced?

Answer 7

Pachytene of prophase I (when crossing over occurs )

anaphase I : independent assortment (random mixtures of maternal and paternal chromosomes at each pole)

Question 8

Define aneuploidy

Answer 8

Abnormal number of chromosomes

Question 9

Define monosomy

Answer 9

When a chromosome is missing from a pair

Question 10

what happens during leptotene?

Answer 10

replicated chromosomes become to condense to become thin threads

the two sister chromatids are to close to distinguish apart

Question 11

what happens during zygotene?

Answer 11

synapsis(alignments) of homologous maternal/paternal chromosome to form bivalents

Question 12

what happens during pachytene?

Answer 12

the pairs of chromosomes become condensed and coiled.

crossing over occurs

chromosomes split into sister chromatids

Question 13

what happens during diplotene?

Answer 13

hoologous chromosomes begin to migrate apart

chromosomes only held together by chiasmata

Question 14

what happens during diakinesis ?

Answer 14

chromosomes fully condensed now ; chiasmata and bivalents fully visible

nucleolus/nuclear envelope disappears