Meiosis

Question 1

Describe interphase of meiosis

Answer 1

G1: cell synthesis organelles such as mitochondria and ribosomes. Manufacture proteins. Builds up large store of energy.

S: DNA replicates, centrioles replicates

G2: continues to build up energy and manufacture proteins and organelles

Question 2

Outline prophase I

Answer 2

Behaviour of chromsomes:
Chromatin condense into chromosomes

Behaviour of centrioles:
- move to opp end of people andform spindle fibres
- spindle fibre attach to controversial of chromosome via kinetochore

Behaviour of chromosomes:
- homologous chromosome undergo synapsis forming chiasmata
- chiasmata allows corssing over between no sister chromatids of homologous chromosomes

Question 3

What is synapsis

Answer 3

Chiastma formed between non-sister chromatids of homologous chromsomes forming bivalent

Question 4

Characteristics of homologous chromsomes

Answer 4

• same size
• centromeres in same position
• same genes but have different alleles
• identical sequence of gene loci

Question 5

Why 2 sister chromatids are genetically identical before crossing over while a pair of homplpgos chromosomes are not

Answer 5

1. Sister chromatids are 2 identical DNA molecules with the same DNA sequence as a result of DNA replication during S phase
2. Homologous chromsomes are inherited from different parent who are gentically different hence while they have the same genes, they may hae different alleles

Question 6

Describe how crossing over occurs

Answer 6

Homologous chromsomes undergo synapsis where chiasmata is formed between non-sister chromatids of homologous chromsomes forming a bivalent. Chiasmata allows crossing over of non sister chromatids in bivalent.

DNA nucleotides of homologous regions in nonsister chhromatids break and rejoin
Resulting in exchange of genetic material forming new combinations of allele

Question 7

Outline Metaphase I

Answer 7

Bivalent ranged along metaphase plate

Independent assortment occurs
- orientation of chromosomes in bivalent is independent of that of other bivalent
- subsequent separation of homologous chromsomes in anaphase I results in random assortment of maternal and paternal chromosomes in each gamete

Question 8

Outline anaphase I

Answer 8

Homologous chromosomes separate and move to opposite ends of the pole as kinetochore microtubules shorten

Non-kinetochore microtubules shorten causing cell to lengthen

Question 9

Outline telophase I

Answer 9

Spindle fibres disintegrate
Nuclear envelope and nucleolus reforms

Cytokinesis: 2 daughter nuclei contains 1 et of chromosome each

Question 10

Importance of meiosis

Answer 10

Prevent doubling of chromsomes during sexual reproduction
- meiosis produce haploid gametes
- fusion of male and female gametes zygote and restore diploid number of chromsomes

Generate genetic variation
- crossing over in prophase I forms new combination of alleles
- independent assortment in metohase I results in random assortment of maternal and partner all chromsomes in each gamete

Fertilisation
- fusion of random gametes

Question 11

What is numerical aberration

Answer 11

Failure to separate
- homologous chromsomes in anaphase I
- sister chromatids in anaphase II

Results:
Aneuploidy or polyploidy

Question 12

What is aneuploidy and polyploidy

Answer 12

Aneuploidy: abnormal number of individual chromsomes due to failure to separate homologous chromsomes in anaphase I or sisterchromatids in anaphase II

Question 13

What is occurring during the vertical drop of DNA per cell graph

Answer 13

Cytokines