Mitosis and meiosis Flashcards
Schwann theory on mitosis
Cells come from cells
Virchow theory on mitosis
Cells arise through binary fission
Stages of mitosis
Prophase - metaphase - anaphase - telophase - cytokinesis
What happens in early prophase?
Condensing replicated chromosomes
What happens in late prophase?
Prometaphase
Microtubules emerge from centrosome at poles of mitotic spindle extend into nuclear region reaching chromosomes. Some of the spindle microtubules attach to kinetochores. Other spindle microtubules make contact with microtubules coming from opposite pole
What happens in metaphase?
Mitotic spindle is fully formed. Chromosomes midway between spindle poles
What happens in anaphase?
Two centromeres of each chromosome come apart, separating the sister chromatids. Proteins of kinetochores, powered by ATP, walk newly separated daughter chromosomes along microtubules towards opposite poles of the cell. Microtubules attached to kinetochores shorten. Spindle microtubules not attach lengthen. Poles move farther apart
What happens in S phase?
Interphase - each chromosome is duplicated by the cell
How many chromosomes are there after DNA synthesis?
46 chromosomes - 92 chromatids
Characteristics of mitosis
- Genetically identical cells
- Diploid cells
- Takes place throughout an organism’s lifetime
- Involved in asexual reproduction
Characteristics of meiosis
- Genetically unique cells
- Haploid cells
- Sexual reproduction
- 4 haploid cells produced
What happens during meiosis?
- Interphase: DNA replication
- Prophase 1: chromosomes join
- Metaphase 1: homologs align in centre of cell
- Anaphase 1: homologous chromosomes separated
- Anaphase 2: sister chromatids separate
What holds homologous chromosomes together?
Synaptonemal complex
Where does crossing over occur?
Between homologous chromosomes
Non-sister chromatids of homologous ch
Characterics of spermatozoa
23 chromosomes, n=1
What is an egg?
A secondary oocyte in metaphase ii
N number of zygote
2
How many primary coccyges in ovary?
300,000
What is produced by meiosis in males?
Spermatozoa
How are secondary spermatocytes produced?
Spermatogonium undergoes mitosis twice to produce primary spermocyte (meiosis i) and then secondary spermatocyte (meiosis ii)
What is a germ cell?
Any cell that gives rise to gametes
What is a primordial germ cell?
Diploid cells that arise through mitosis. Arise in primitive streak and migrate via the gut of an embryo to the developing gonads. Once in gonads, they form oogonium (female fetus). At 7 months, oogonia turn into primary oocytes. In males, oogonium = spermatogonia
What does ss mean?
Chromosome made from one chromatid
What does ds mean?
Chromosome made from two chromatids
True or false, germ cells can only undergo meiosis
False
True or false, meiosis is only completed in females once the oocyte is fertilised?
True
Do males run out of primary oocytes?
No
