4.3 - meiosis Flashcards
gamete
sex cell (sperm or egg)
sperm is produced
in the testes
eggs (ova/ovum) are produced
in the ovaries
are gametes haploid or diploid
haploid
fertilization
the fusion of a sperm and egg to form a zygote which divides and multiplies to make an embryo
zygote
diploid fertilized egg
meiosis
the process of making gametes in sexually reproducing organisms
3 main steps to meiosis
interphase
meiosis |
meiosis ||
interphase (meiosis)
DNA replicates and the cell prepares for meiosis
occurs in a spermatocyte and oocyte which are both diploid cells
spermatocyte
male diploid sex cell
oocyte
female diploid sex cell
homologous chromosomes desc
pair of chromosomes similar in shape and size
homologous pairs carry genes controlling the same inherited traits
(humans have 23 pairs of homologous chromosomes, 22 autosome pairs and 1 sex chromosome pair)
homologous pairs are also called
tetrads because a homologous chromosome pair consists of 4 chromatids
meosis 1- prophase desc
synapsis- chromosomes pair up beside each other
crossing over- genetic information is mixed
nuclear membrane disappears and spindle fibres form
what is crossing over?
while synapsis is when a paternal and maternal chromosome pair to form a tetrad, chromosomes SEGMENTS are exchanged between two non-sister chromatids to mix up the genetic information
meiosis 1 - metaphase 1
homologous chromosomes line up in the middle of the cell in random assortment
spindle fibres move chromosomes to centre
what is random assortment?
homologous pairs of chromosomes will line up in the middle of the cell. The maternal and paternal arrangement is randomized, allowing for variation in the gametes
meiosis 1- anaphase 1
spindle fibres pull toe homologous chromosomes to opposite poles
meiosis 1- telophase 1
chromosomes reach the poles
spindle fibres dissolve
nuclear membrane forms
meiosis 2- prophase 2
nuclear membrane disappears
spindle fibres form in each new cell
meiosis 2- metaphase 2
chromosomes line up in the middle
meiosis 2- anaphase 2
centromeres separate and chromatids are pulled to opposite poles
meiosis 2- telophase 2
chromatids reach the poles
spindle fibres dissolve
FOUR new nuclear membranes form
gametogenesis is composed of
spermatogenesis
oogenesis
spermatogenesis
production of sperm cells in the testes (4 viable sperm cells are produced)
oogenesis
production of egg cells in the ovaries (1 viable egg cell is produced and is much larger than a sperm cell)
karyotype
a photograph of stained chromosomes sorted and arranged by size and type
each homologous set in a karyotype is made of
2 homologues
sex determination in some animals
humans (xx= female xy= male) birds (zw=female zz=male) reptiles (temperature warm egg= female cold egg = male) fish (males become female w/ age) insects (fertilization fertilized = female etc.)
