6.3 Meiosis

Question 1

what are homologus pair of chromosomes

Answer 1

• a pair of chromosomes of which one is maternal (from egg) and one is paternal (from sperm).
• Carry the same genes at same loci, but could be different alleles of the same genes.

Question 2

how are genetic differences caused in mieosis

Answer 2

Independent assortment
> during metaphase 1 homologous pairs of chromosomes line up opposite each other on either side of the equator

> random which side paternal and maternal chromosome pair aligns
each gamete receives different combinations of maternal and paternal chromosomes
any sperm cell could fertilise the egg cell

crossing over:
> crossing over genetic material occurs between non-sister chromatids of bivalents forming chiasma
> breaks occur in genetic material where chromatids cross over and parts of the chromatids are exchanged between homologous pairs
genetic material is transferred between sister chromosomes

> results in new combination of alleles in resulting gametes

Question 3

what happens in prophase 1

Answer 3

Starts the same as in mitosis (chromosomes condense nuclear envelope disappears spindle fibers form)
Difference to mitosis: Homologous chromosomes pair up forming bivalents chromatids entangle cross over

Question 4

what happens in metaphase 1

Answer 4

Similar to mitosis, except pair of homologous chromosomes line up in the middle.
any homologous chromosome can end up facing either end of the pole, which is called independent assortment results in genetic variation

Question 5

what happens in anaphase 1

Answer 5

the homologous chromosomes are pulled apart to opposite poles of the cell as spindle fibres shorten, but the chromatids stay joined
the exchange of DNA from crossing over occurs the points of which the chromatids breaks and rejoin is called chiasmata
the sister chromatids are no longer identical

Question 6

what happens in telophase 1

Answer 6

Essentially the same in mitosis the chromosomes reach the other end of the pole the nuclear envelope reforms chromosomes uncoil.

Question 7

what happens in cytokenisis

Answer 7

The process by which the cell splits into two at the end of mitosis, forming a new nuclear envelope and plasma membrane

Question 8

whats binary fission

Answer 8

The process of cell division in prokaryotic cells

Question 9

stages of binary fission

Answer 9

The circular DNA replicates, both copies attach to the cell membrane. The plasmid also replicates
The cell membrane grows between the replicated DNA and begins to pinch inwards which splits the cytoplasm in two. The new cell wall forms, forming the complete daughter cells

Question 10

whats a diploid cell

Answer 10

an organism or cell having two sets of chromosomes one from each parent

Question 11

whats a haploid cell

Answer 11

half the number of chromosomes 23

Question 12

whats meiosis

Answer 12

Cell division where the nucleus divides twice to produce 4 non genetically identical daughter cells makes haploid cells

Question 13

what happens in prophase 2

Answer 13

The chromosomes which are still two chromatids, condense again spindle reforms and nuclear envelope begins to break

Question 14

what happens in metaphase 2

Answer 14

Chromosomes are pulled by spindle fibers to middle
Due to crossing over they are no longer identical so there is more independent assortment

Question 15

what happens in anaphase 2

Answer 15

as spindle fibres shorten and centromeres divide Individual chromatids pulled to each side of pole like in mitosis

Question 16

what happens in telophase 2 and cytokenisis

Answer 16

Chromatids uncoil and become chromatin the nuclear envelop reforms again
Cytokineses results in the division of 4 haploid cells which are genetically different from each other and parent cells due to independent assortment and crossing over