Miosis Flashcards
Sexual reproduction
Producing offspring via gametes
Depends on miosis, DNA recombination
Consists of n cells
Fertilization
The nuclei of an egg and a sperm meet producing a zygote, further mixing DNA
Fertilization cycle
Fertilization (2n)– miosis(2n)–spore(n)–mitosis–gametes
Spores
Divide using mitosis
Animals
2n phase dominates miosis directly followed by gamete formation
Males miosis
Each miotic cell turns into a functional sperm
Females miosis
1/4 nuclei turn into a functional egg cell
Most plants, some fungi
Alternate n and 2n generations. Fertilization produces 2n sporophytes. Miosis occurs and n spores are produced
Spores in plants
Become n gametophytes which can mature into gametes. Identical because miosis does not occur
Most fungi
2n phase is limited to only the zygote
Immediatly after fertilization miosis produces n, where mitosis can occur
Fungi fertilization
2, n gametes (+)/(-) meet. 4, n cells produced from 1 2n cell
Miosis
Produces 2 different cells. Occurs in specialized tissues producing gametes and spores
Homologous chromosomes have
The same genes in the same order in the DNA, but might have different alleles
Homologous chromosomes are made of
1 paternal chromosome and 1 maternal chromosome
Roles of miosis
Increase variability and half the chromosome number
Each n cell carries half the genes for a homologous chromosome
Genetic recombination purpose
Have maternal and paternal genes passed on
Meiocytes
Cells that divide by miosis. S phase occurs, creating 2 daughter cell SNA for G2 phase
Miosis I
Synapsis occurs. Chromosomes pair lengthwise gene for gene and recombination occurs. 2 daughter cells with n (double) chromosomes are produced
Miosis II
Sister chromatids are separated. 4 cells with n chromosomes are created
Internkinesis
Interphase that seperates the 2 miotic cycles. No DNA replication occurs
Prophase I
Duplicated chromosomes fold and condense
pairing and synapsis occurs
recombination between homologous pairs
Spindle fibers form
Synapsis
Homologous pairs line up side by side forming tetrads
Tetrads
A make up of 4 chromatids
Prometaphase I
Nuclear membrane breaks
Spindle fibres connect
Kinetochore microtubules connect to 1 sister chromatid
Metaphase I
Spindles line chromosomes on the metaphase plate
Anaphase I
Double structured sister chromosomes are divided to the poles
Telophase I
Brief, nuclear membrane may reform
Interkinesis
Spindle fibers disassemble and become 2 spindle fibers for miosis II
Prophase II
Chromosomes condense
Prometaphase II
Nuclear membrane breaks down, spindle fibers enter and attach
Metaphase II
Spindle movement brins chromosomes to the metaphase plate
Anaphase II
Sister chromatids separate and move to the poles (now are single chromosomes)