Meiosis - Making Sex Cells

Question 1

What is Meiosis?

Answer 1

A process used to make haploid gamete cells from diploid cells in the ovaries and testes
Used in sexual rep.
Consists of one replication of DNA in Interphase and two cell divisions (Meiosis I & Meiosis II)
Sometimes referred to as REDUCTION DIVISION cause it’s a form of cell division that produces daughter cells with fewer chromosomes than the parent cells

Question 2

What is Recombination?

Answer 2

The products of Meiosis have different combinations of genes
Offspring are genetically different from one another and their parents

Question 3

Meiosis I : Interphase I

Answer 3

Like somatic cells, germ cells (gamete producing cells) proceed through the growth and synthesis phases of Interphase before dividing
Chromosomes are replicated in the S phase of Interphase, allowing the Germ cell to begin meiosis with duplicated
chromosomes
Each chromosome is made up of a pair of identical sister chromatids held together by a centromere

Question 4

Meiosis I : Prophase I

Answer 4

Each pair of homologous chromosomes line up side by side (synapsis)
Homologous chromosomes are not identical : same genes, diff. alleles
Each pair of Homologous Chromosomes is called a Tetrad (total of 4 chromatids)
“Non-sister chromatids” refers to side by side chromatids that are non-identical

Question 5

Meiosis I : Metaphase I

Answer 5

Spindle fibers attach to centromeres of each homologous chromosomes
Spindle fibers guide each Tetrad to the equator of the cell (metaphase plate)
Tetrad align in the center of the cell as homologous chromosomes - not single file like mitosis

Question 6

Meiosis I : Anaphase I

Answer 6

Tetrads break up
Spindle fibers shorten and homologous chromosomes separate and are pulled to opposite poles
Sister chromatids are still held together by centromeres so they don’t split like they do in mitosis

Question 7

Meiosis I : Telophase I

Answer 7

Homologous chromosomes uncoil and spindle fibers disappear
Cytokinesis divides cytoplasm into 2
Nuclear membrane forms around each group of Homologous Chromosomes
Each new cell contains one set of sister chromatids and is now haploid
Chromosome replication does not take place before the next phase of meiosis
NO SECOND INTERPHASE
NO DNA REPLICATION

Question 8

Meiosis II

Answer 8

The phases in Meiosis I & II are similar
Each cell proceeds through Prophase II, Metaphase II, Anaphase II, and Telophase II
Each cell that enters Meiosis II is haploid but with double-stranded chromatids
At the end of Meiosis II, the daughter cells are still haploid, but the contain single-stranded chromosomes

Question 9

Meiosis II : Prophase II

Answer 9

New spindle fibers form

Question 10

Meiosis II : Metaphase II

Answer 10

Chromosomes align on the equator of the cell
Spindle fibers attach to centromeres

Question 11

Meiosis II : Anaphase II

Answer 11

Centromeres split
Sister chromatids go to opposite sides of the cell

Question 12

Meiosis II : Telophase II

Answer 12

Cleavage develops in the cell membrane
Nuclear membrane reforms
Chromatids unravel into chromatin

Question 13

What happens at the end of Meiosis II?

Answer 13

Four Haploid cells are formed