MEOISIS
DEF: a process by which a single cell divides twice to produce 4 daughter
cells, they have HALF the number of chromosomes of the parent cell –
haploid
Meiosis 1 reduction division which results in parent cell (diploid 2n) dividing
into 2 cells, each with 23 chromosomes each (haploid number n)
Meiosis 2 – copying division which involved the 2 haploid cells (formed in
meiosis 1) to divide again by mitosis to form 4 haploid cells
Mitosis – makes identical body cells (i.e. skin cells, stomach cells repair
damaged cells, growth, replace worn out cells
Meiosis produces sex cells and contributes to genetic variety – gametes (eggs
in females and sperm in males)
Most
body
cells
have 46
chromos
Sperm and eggs cells only have 23 chromosomes – when
omes (92
they come together, 46 chromosomes – fertilized egg
chromati
In the nuclei ds)
chromosomes – DNA strands wrapped around proteins
These histone proteins organise the chromosomes into a compact structure
chromatin enables DNA to fit inside small structures
Chromosomes (2 chromatids: each of the two threadlike strands into which a
chromosome divides longitudinally during cell division. Each contains a
double helix of DNA) made up of DNA, this genetic information is carried to
the next generation by the chromosomes
Reduction division:
INTERPHASE:
, DNA replication, growth, carrying out cell functions
DNA replication ensures that each new cell formed by cell division gets the
same genetic material as present in the mother cell (prevents it being halved
in mitosis)
46 chromosomes duplicated
MEIOSIS 1: a reduction division (results in 2 haploid cells)
PROPHASE 1:
Chromosomes condense and thicken – line up with their homologous pairs
Chromosomes become short and fat and are visible as 2 chromatids joined by
a centromere
Homologous pairs approximately the same size, contain the same type of
genes, in the same locations
The homologous pairs close together are called bivalents
Crossing over – the bivalents (homologous pairs) exchange pieces of their
inner chromatids by breaking and reforming their DNA
Some paternal genes change place with maternal genes and so forth
DEF: a process by which a single cell divides twice to produce 4 daughter
cells, they have HALF the number of chromosomes of the parent cell –
haploid
Meiosis 1 reduction division which results in parent cell (diploid 2n) dividing
into 2 cells, each with 23 chromosomes each (haploid number n)
Meiosis 2 – copying division which involved the 2 haploid cells (formed in
meiosis 1) to divide again by mitosis to form 4 haploid cells
Mitosis – makes identical body cells (i.e. skin cells, stomach cells repair
damaged cells, growth, replace worn out cells
Meiosis produces sex cells and contributes to genetic variety – gametes (eggs
in females and sperm in males)
Most
body
cells
have 46
chromos
Sperm and eggs cells only have 23 chromosomes – when
omes (92
they come together, 46 chromosomes – fertilized egg
chromati
In the nuclei ds)
chromosomes – DNA strands wrapped around proteins
These histone proteins organise the chromosomes into a compact structure
chromatin enables DNA to fit inside small structures
Chromosomes (2 chromatids: each of the two threadlike strands into which a
chromosome divides longitudinally during cell division. Each contains a
double helix of DNA) made up of DNA, this genetic information is carried to
the next generation by the chromosomes
Reduction division:
INTERPHASE:
, DNA replication, growth, carrying out cell functions
DNA replication ensures that each new cell formed by cell division gets the
same genetic material as present in the mother cell (prevents it being halved
in mitosis)
46 chromosomes duplicated
MEIOSIS 1: a reduction division (results in 2 haploid cells)
PROPHASE 1:
Chromosomes condense and thicken – line up with their homologous pairs
Chromosomes become short and fat and are visible as 2 chromatids joined by
a centromere
Homologous pairs approximately the same size, contain the same type of
genes, in the same locations
The homologous pairs close together are called bivalents
Crossing over – the bivalents (homologous pairs) exchange pieces of their
inner chromatids by breaking and reforming their DNA
Some paternal genes change place with maternal genes and so forth
