6.3 (2.1.6) Meiosis

why is meiosis known as reduction division

each cell (gamete) formed contains half of the chromosome number of the parent cell

define homologous chromosomes

chromosome pairs, one from each parent, that are similar in length, gene position, and centromere location

define allele

different versions of the same gene

describe meiosis 1

reduction division when the pair of homologous chromosomes are separated into two haploid cells

describe meiosis 2

mitotic division in which the pairs of chromatids present in each daughter cell are separated to form two more cells. four haploid cells produced in total

describe prophase 1

1) chromosomes condense

2) nuclear envelope breaks down

3) nucleolus disappears

4) spindle fibres are formed

5) the homologous chromosomes pair up forming bivalents

6) crossing over occurs

describe metaphase 1

1) homologous pairs of chromosomes assemble along metaphase plate

2) independent assortment of chromosomes occur

define independent assortment

the random separation of homologous chromosomes in meiosis 1 that produces genetic variation

describe anaphase 1

homologous chromosomes are separated and the chromatids stay joined to each other

define chiasmata

the point at which chromatids break and rejoin

describe telophase 1

1) chromosomes assemble at each pole

2) nuclear membrane reforms

3) chromosomes uncoil

4) 2 new haploid daughter cells are formed

describe prophase 2

1) chromosomes condense and become visible

2) nuclear envelope breaks down and spindle formation begins

describe metaphase 2

1) individual chromosomes assemble on the metaphase plate

2) independent assortment occurs

describe anaphase 2

sister chromatids of the individual chromosomes pulled to opposite poles after division of centromere

describe telophase 2

1) chromatids assemble at opposite poles

2) chromosomes uncoil and form chromatin

3) nuclear envelope reforms and nucleolus becomes visible

4) in total 4 haploid non-identical daughter cells are formed