Topic 10: Genetics and Evolution HL

Question 1

Germ line cell

Answer 1

A diploid cell that is destined to become a gamete

Question 2

somatic cell

Answer 2

body cell

Question 3

chiasma

Answer 3

point of crossing over of non-sister chromatids of a homologous pair of chromosomes

Question 4

recombination

Answer 4

exchange DNA between non-sister chromatids as a direct results of crossing over

Question 5

chromosome replication

Answer 5

At the start of meiosis, the chromosomes condense and so become visible as two chromatids, called sister chromatids.
Pairing, or synapsis, now occurs where two homologous chromosomes come to align beside each other (this does not happen in mitosis!)
This complex is referred to as a tetrad (composed of 4 chromatids) or a bivalent (composed of a pair of chromosomes).

Question 6

phases of meiosis

Answer 6

Meiosis I separates homologous chromosomes.
Crossing-over and recombination of DNA occurs during Prophase I.
Separating homologous chromosomes reduces the chromosome number by half.

Meiosis II separates sister chromatids of each chromosome.
There is no DNA replication between meiosis I and meiosis II.
Separating sister chromatids does not reduce the chromosome number.

Question 7

meiosis I

Answer 7

Homologous chromosomes separate in meiosis I.
This first meiotic division is unique, because:
sister chromatids remain associated with each other
The homologous chromosomes behave in a coordinated manner in prophase
Homologous chromosomes exchange DNA, leading to genetic recombination
The number of chromosomes is reduced by half (reduction division)

Question 8

Meiosis II

Answer 8

Sister chromatids separate in meiosis II.
This second meiotic division resembles mitosis.
There is no interphase separating meiosis I and II.
The replicated chromosomes are separated into chromatids.
The number of chromosomes remains the same from the start to the end of meiosis II