MITOSIS AND MEIOSIS Flashcards
Spermatogenesis vs Oogenesis
Spermatogenesis:
- Produces 4 spermatozoa.
- Small with tightly packed DNA and flagella.
Oogenesis:
- Produces 1 ovum and a polar body.
- Only one gamete is formed.
number gametes
Males: Sperm germline can divide throughout life.
Females: Oocytes are largely fixed before birth, with a limited number.
GAMETE formation timings
Males: Gametes are continuously formed and released.
Females: Gametes are released once per month.
meiosis overview
Occurs only in germ cells for sexual reproduction.
Reduces chromosome number by half (from diploid to haploid) through 2 divisions.
Germline segregated early in animals (not the same in plants).
Mutations in somatic cells are not inherited.
mitosis overview
Transmits the entire genome to two daughter cells.
Ploidy is maintained.
Interphase (G1, S, G2) prepares for replication.
G0 is the state of non-proliferating cells.
Highly regulated process.
chromatin condensation in mitosis
Condensin proteins organize loose chromatin into visible chromosomes.
During interphase, chromatin is loosely distributed around the nucleus.
Condensin binds to DNA and folds chromatin into individualized chromosomes.
karyotype
A photograph of the complete set of chromosomes.
Grouped in homologous pairs, arranged by size.
Organism-specific in appearance and number.
Homologous Chromosome Pairing (Meiosis)
Programmed DNA DSB (double-strand breaks) initiate at the beginning of meiosis, starts recombination
Non-sister chromatids are used for repair, pulling homologous chromosomes together.
Synaptonemal complex forms, keeping homologous chromosomes (HC) close until the DSB is repaired.
Crossovers hold chromosomes together at the chiasma.
importance of crossovers
Allow for recombination (new allele combinations).
Increases genetic variation.
Prevents the accumulation of harmful mutations.
sex chromosomes and recombination
Two systems: XX (F) - XY (M) or ZW (F) - ZZ (M).
Sex chromosomes derived from autosomes after the loss of recombination.
During meiosis, crossovers occur in pseudo-autosomal regions, ensuring pairing and correct segregation.
stages of mitosis
Sister chromatids are produced by DNA replication during S phase, held together by centromere
One kinetochore attaches to each sister chromatid. during metaphors, microtubules attach to kinetochore to allow for seperation
Sister chromatids are separated.
Cytokinesis divides the two daughter cells.
Sister Chromatids Adhesion and Separation
Cohesin proteins hold sister chromatids together after DNA replication.
In prophase, cohesin holds the chromatid arms, but by metaphase, arms are free.
In anaphase, cohesin at the centromere is degraded, allowing separation.
binary fission in bacteria
Asexual reproduction via division of a single circular chromosome.
Mitochondria and chloroplasts divide similarly, due to their bacterial origin.
chromaosomal regions
sister chromatids - identical copies of chromosome
euchromatin - lighter colour as less condense
heterochromatin - darker bands as more condensed
centromeres - constitutive heterochromatin, repetitive DNA and bind to kinetochore during mitosis
temoleres at end - made up of constitutive heterochromatin
kinetochore
protein structure located at centromere of each sister chromatid, is an attachment site for spindle fibres to attach to separate the chromatids
