meiosis Flashcards
what is meiosis?
special type of cell divison that occurs only in reproductive organs.
what do meiosis make?
gametes
what are the functions of meiosis
meiosis 1: reduction division
meiosis 2: further divide the cell
what is the division of chromosome number?
body cells= 46 chromosomes (2n)– diploid
gametes= 23 chromosomes (n)– haploid
meiosis– interphase
same as mitosis= cell grows and replicates DNA
= chromosome is made up of a pair of identical sister chromatids held together by a centermer
prophase 1
homologous chromosomes align and form a bivalent
nuclear membrane disappears
spindle fibers begin to form
crossing over occurs
what so homologous chromosomes contain?
the same genes- but since they came from diff parents they can have different alleles
crossing over?
the exchange of genetic material b/w non sister homologous chromatids
may not happen at all
what is a bivalent?
the structure of the 2 non sister homologues pairs crossing over
what is a bivalent?
the structure of the 2 non sister homologues pairs crossing over, where the sister chromatids may touch and break.
the region where crossing over occurs?
chiasma
result of crossing over?
chromatids that are a mixture of paternal and maternal alleles. crossing over may happen multiple times between diff chromatids within the same homologous pair.
metaphase 1
spindle fibers attach to the centromere of each chromosome
spindle fibers pull each bivalent to the center of the cell
random assortment occurs
random assortment?
another way to ensure genetic variability
what happens during random assortment
bivalents line up on the equator of the cell randomly
paternal chromosomes// maternal chromosomes= that some gametes will obtain maternal and others will get paternal genes
or, parental chromosomes could be on both sides of the equator= gametes to contain a mixture of maternal and parental chromatids.
anaphase 1
The homologous chromosomes separate
and move to opposite poles of the cell.
centromere does not split as in mitosis=sister chromatids are held together, moving one chromosome to each of the poles.
telaphase 1
may or may not occur– depends on the type of meiosis is occurring
chromosomes begin to uncoil and the spindle fibers disappear.
The cytoplasm is divided and the nuclear
membrane begins to form around the pairs of
homologous chromosomes.
does DNA replication occur in meiosis 2??
no, Because each chromosome already consists of two chromatids,
meosis 2
identical to mitosis
end product of meiosis
4 non identical haploid cells
