Meiosis Flashcards
Classifications of cells present in sexually reproductive organisms
Somatic cells: Diploid number of chromosomes
Gametes: Haploid number of chromosomes (sperm and ova)
What are the results of meiosis?
Reduction of chromosome number
Segregation of alleles
Random assortment of homologs
Shuffling the genetic material by crossing over
Meiosis name in males and females
Males = Spermatogenesis (production of sperm in the seminiferous tubules of the testes)
Females = Oogenesis (production of ova in the ovaries)
Process of spermatogenesis
Stage 1: Division of germline epithelium by mitosis into spermatogonia
Stage 2: Spermatogonia undergo growth
Stage 3: Two meiotic divisions of spermatocytes produces four daughter cells
Stage 4: Haploid cells differentiate to form sperm cells
Stage 5: Sperm cells nourished by Sertoli cells
Process of oogenesis
Stage 1: Start at fetal development with oogonia forming by mitosis
Stage 2: Oogonia start meiosis but the process is arrested at prophase I
Stage 3: After puberty, follicles continue developing each month through FSH secretion
Stage 4: Follicles complete meiotic division forming two unequally sized cells. Polar body is degraded and secondary oocyte forms from larger cell
Stage 5: Secondary oocyte begins second meiotic division which is arrested at prophase II until fertilisation
Stage 6: It is released from the ovary (ruptured follicle develops into corpus luteum) and, if fertilisation occurs, will complete meiosis
Stage 7: The second meiotic division will produce an ovum and a second polar body
What are the stages of meiosis?
Meiosis I
Meiosis II
Meiosis II has no interphase
What are the events of interphase I?
Chromosomes replicated during S phase
Duplicated chromosomes contain two identical sister chromatids attached at the centromere
Centriole pairs replicate
What occurs during the first meiosis division?
Cell division reduces the number of chromosomes by half
Stages:
* Prophase I
* Metaphase I
* Anaphase I
* Telophase I
What are the five stages of prophase I
Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis
What occurs during leptotene
First stage of prophase I
Chromosomes condense
What occurs during zygotene?
Second stage of prophase I
Synapsis occurs (homologous chromosomes pairing to form a tetrad along their length)
Tetrad = two chomosomes/four non-sister chromatids
What occurs during pachytene?
Third stage of prophase I
Crossing over occurs in syneptonemal complexes
What occurs during diplotene?
Fourth stage of prophase I
Homologous recombination (chiasmata formed by migration of DNA strands between DNA molecules in a reciprocal manner)
What occurs during diakinesis?
Fifth stage of prophase I
Terminalisation of chiasmata
Chromosomes reach maximal condensation
What occurs during metaphase I?
Tetrads align along the metaphase plate
Random orientation of homologous pairs to the poles of the cell are random
Metaphase I is the shortest phase of meiosis I
What occurs during anaphase I?
Homologous chromosomes move towards the poles
Sister chromosomes remain attached at the centromeres
What occurs during telophase I?
Each pole now has a haploid number of chromosomes
Cytokinesis occurs subsequent to telophase forming two daughter cells
Prophase II and Metaphase II
Same as in mitosis
What occurs during anaphase II?
Sister chromatid separate
What occurs during telophase II?
Nuclei form
Cytokinesis occurs subsequent to telophase forming four haploid cells
