Stages of meiosis

Question 1

What is the difference between meiosis I and meiosis II?

Answer 1

Meiosis 1 is the first division in the reduction division when the pairs of homologous chromosomes are separated

each intermediate cell will only contain one full set of genes instead of two (haploid)

Meiosis II - similar to mitosis, the pairs of chromatids in each daughter cell are separated forming two more cells, four daughter haploid cell are produced in total

Question 2

What happens in prophase 1?

Answer 2

chromosomes condense,

nuclear envelope disintergrates

nucleolus dissapear

spindle formation begins

difference from prophase in mitosis:

homologous chromosomes pair up, forming bivalents

brought together by the chromatids entangling

this is called crossing over

Question 3

What happens in metaphase I?

Answer 3

same as metaphase in mitosis except the homologous pairs of chromosomes assemble along the metaphase plate instead of the individual chromosomes

orientation of each homologous pair on the metaphase plate is random and independent of any other homologous pair

this is called independent assortment

independent assortment can result in many different of alleles facing the poles

results in genetic variation

Question 4

What happens in anaphase I?

Answer 4

spindles contract, separating the homolgous pairs

sections of DNA on sister chromatids, which became entangled, break off and rejoin, causes exchange of DNA

the points at which chromatids break and rejoin are called chiasmaa

this forms recombinant chromatids, genetic variation arises from this new combinations of alleles

sister chromatids are no longer identical

Question 5

What happens in telophase I?

Answer 5

essentially the same as telophase in mitosis

chromosomes assemble at each poles, envelope reforms, chromosomes uncoil

cell undergo cytokinesis and the reduction of chromosome number from diploid to haploid is complete

Question 6

What happens in prophase II?

Answer 6

chromosomes, which still consist of two chromatids, condense

nuclear envelope breaks down and spindle formation begins

Question 7

What happens in metaphase II?

Answer 7

differs from metaphase I, individual chromosomes assemble on the metaphase

due to crossing over, chromatids are no longer identical so there is independent assortment

and more genetic variation

Question 8

What happens in anaphase II?

Answer 8

unlike anaphase I, II results in the chromatids of the individual chromosomes being pulled to opposite poles after division of the centromeres - same as anaphase in mitosis

Question 9

What happens in telophase II?

Answer 9

chromatids assemble at the poles

chromosomes uncoil and form chromatin again

nuclear envelope reforms and the nucleolus becomes visible

cytokinises occurs, form 4 genetically different haploid daughter cells