HGA2 - Meiosis

Question 0

Advantage of sex

Answer 0

shuffling of genes

• provides variation on which selection can act

Question 1

The problem with sex

Answer 1

• only half the parent genes are transmitted from each parent - each individual is less efficient at passing its genome to next generation (problem compounded with 2 sexes)
• sex is dangerous

Question 2

Genetic info

Answer 2

• genetic info stored in nucleus in chromosomes
• most cells diploid with 2 sets of chromosomes
- 1 from mother, 2 from father
• matched pairs = homologous chromosomes

Question 3

Interphase (meiosis)

Answer 3

• chromosomes duplicated (2 identical copies called sister chromatids)
• DNA wound around histone proteins, each coils into helical fiber

Question 4

Stages of Meiosis

Answer 4

MEIOSIS I
Prophase
• Leptotene
• Zygotene
• Pachytene
• Diplotene
• Diakinesis

Metaphase I
Anaphase I
Telophase I

Interkinesis

MEIOSIS II
Prophase II
Metaphase II
Anaphase II
Telophase II

Question 5

Prophase I – Leptotene

Answer 5

• chromosomes thicken and become visible
• chromatids remain invisible
• centromeres begin to move to opposite poles

Question 6

Prophase I – Zygotene

Answer 6

• homologous chromosomes enter synapsis (recognize each other and align)

Question 7

Prophase I – Pachytene

Answer 7

• synapsis complete – homologs completely aligned
• homologous chromosomes form bivalent/tetrad
- 2 pairs of sister chromatids, 4 chromatids total
• crossing over/recombination

Question 8

Crossing over/recombination

Answer 8

• genetic exchange between nonsister chromatids of homologous pairs

Question 9

Synapsis also known as

Answer 9

synaptonemal complex

Question 10

Chiasma

Answer 10

where chromosomes connect at crossover sites

Question 11

Prophase I – Diplotene

Answer 11

• synaptonemal complex dissolves

* bivalent/tetrad pulls apart slightly by connected at crossover site (chiasma)

Question 12

Prophase I – Diakinesis

Answer 12

• chromosomes thicken and shorten (condense more0
• nuclear membrane breaks down
• spindle forms

Question 13

Metaphase I

Answer 13

• tetrads/bivalents line up along metaphase plate

* each chromosome of a homologous pair attaches to opposite poles (sisters to the same side)

Question 14

Anaphase I

Answer 14

• centromere doesn’t divide (protected by separase)
• chiasma migrate off chromatid ends
• each chromosomes still consists of 2 sister chromatids
• homologous chromosomes to different poles

Question 15

Telophase I

Answer 15

• nuclear envelope re-forms
• cells with half the number of chromosomes, 2 sister chromatids
• begins meiosis with 46 chromosomes, now each daughter cell has 23 chromosomes

Question 16

Interkinesis

Answer 16

• similar to interphase but NO CHROMOSOMAL DUPLICATION

Question 17

Prophase II

Answer 17

• choromosomes condense
• centrioles move toward the poles
• the nuclear envelope breaks down at the end of prophase II

Question 18

Metaphase II

Answer 18

• chromosomes align at the metaphase plate

* sister chromatids attach to spindle fibers from opposite poles

Question 19

Anaphase II

Answer 19

• centromeres divide

* sister chromatids move to opposite poles

Question 20

Telophase II

Answer 20

• chromosomes begin to uncoil

* nuclear envelopes and nucleoli re-form

Question 21

Cytokinesis

Answer 21

• the cytoplasm divides, forming 4 new haploid cells

Question 22

Recombination

Answer 22

• chiasma formation

* genetic material from 1 parent changes to the other parent genetic background

Question 23

Aneuploidy

Answer 23

• cells with more/less DNA than a normal cell

eg Down syndrome

Question 24

Polyploidy

Answer 24

• cells with many genomes

immediate speciation, human agriculture