Chromosomes and meiosis
- made of a strand of DNA wrapped around proteins called histones
- Chromosome = coloured body (absorb dye easily), visible under microscope
SOMATIC CELLS OF DIPLOID ORGANISMS - number of chromosomes in each cell the same (22
pairs of chromosomes and 1 pair of gonosome -sex determining )
- Homologous chromosome: 2 chromosomes, same size and shape, one paternal one
maternal and there are the same genes in place but may have differing alleles
- Chromosome number = specific number of chromosomes in a somatic cell of a species
Meiosis
- Cell division that takes place in reproductive organs (to produce gametes)
- Gametes = haploid (n) ie one chromosome from each homologous pair
- Male and female games fue during fertilization to form diploid zygote (2n)
- Animals: meiosis takes place in testis (spermatogenesis) and ovaries (oogenesis)
- Plants: takes place sporangia (formation of spores)
- Microsporangia = pollen sacs in male anthers
- megasporangia= ovules in female ovaries
- Important: gametes are formed, chromosome number is kept constant for each
generation, genetic variation (crossing over and arrangement of chromosomes at
equator during metaphase)
Process of meiosis: meiosis 1 = reduction division become 2 haploid cells
- Homologous chromosomes come together to form bivalent, one from each pair
goes into daughter cell
- Meiosis 2 = copying division replicate an become 4 haploid cells
- Each chromosome separates into two chromatids, one goes to each daughter cell
therefore there are 4 daughter cells formed
- 2 sister chromatids = 1 chromosome
- 2 chromosomes = 1 homologous pair
- A pair of homologous chromosomes in close contact with each other make a bivalent
CROSSING OVER
, - mutual exchange of pieces of chromosomes so whole groups of genes/alleles are
swapped (late prophase in meiosis 1)
- Replicated homologous pairs come together in a process called synapsis to form
bivalents (swap pieces of inner chromatids) points of crossing over = chiasmata/chiasma
- After crossing over occurs = recombinant pair (outer, unchanged chromatids = parentals)
- Important: genetic variation, new genes can be influenced into species = evolution
Similarities of meiosis and mitosis
- Both are cell division, DNA of parent cell is replicated in interphase, early prophase
chromosomes become short fat, and visible
Differences between meiosis and mitosis
- made of a strand of DNA wrapped around proteins called histones
- Chromosome = coloured body (absorb dye easily), visible under microscope
SOMATIC CELLS OF DIPLOID ORGANISMS - number of chromosomes in each cell the same (22
pairs of chromosomes and 1 pair of gonosome -sex determining )
- Homologous chromosome: 2 chromosomes, same size and shape, one paternal one
maternal and there are the same genes in place but may have differing alleles
- Chromosome number = specific number of chromosomes in a somatic cell of a species
Meiosis
- Cell division that takes place in reproductive organs (to produce gametes)
- Gametes = haploid (n) ie one chromosome from each homologous pair
- Male and female games fue during fertilization to form diploid zygote (2n)
- Animals: meiosis takes place in testis (spermatogenesis) and ovaries (oogenesis)
- Plants: takes place sporangia (formation of spores)
- Microsporangia = pollen sacs in male anthers
- megasporangia= ovules in female ovaries
- Important: gametes are formed, chromosome number is kept constant for each
generation, genetic variation (crossing over and arrangement of chromosomes at
equator during metaphase)
Process of meiosis: meiosis 1 = reduction division become 2 haploid cells
- Homologous chromosomes come together to form bivalent, one from each pair
goes into daughter cell
- Meiosis 2 = copying division replicate an become 4 haploid cells
- Each chromosome separates into two chromatids, one goes to each daughter cell
therefore there are 4 daughter cells formed
- 2 sister chromatids = 1 chromosome
- 2 chromosomes = 1 homologous pair
- A pair of homologous chromosomes in close contact with each other make a bivalent
CROSSING OVER
, - mutual exchange of pieces of chromosomes so whole groups of genes/alleles are
swapped (late prophase in meiosis 1)
- Replicated homologous pairs come together in a process called synapsis to form
bivalents (swap pieces of inner chromatids) points of crossing over = chiasmata/chiasma
- After crossing over occurs = recombinant pair (outer, unchanged chromatids = parentals)
- Important: genetic variation, new genes can be influenced into species = evolution
Similarities of meiosis and mitosis
- Both are cell division, DNA of parent cell is replicated in interphase, early prophase
chromosomes become short fat, and visible
Differences between meiosis and mitosis
