Meiosis Flashcards
why is sexual reproduction important for survival
the varied genes give better chances to individuals for survival
where does meiosis happen
-in cells that will become gametes (not egg or sperm itself)
-spermatocytes and primary oocytes (both produced by mitosis)
how are sperm produced
from spermatocytes via meiosis
how are eggs (secondary oocytes) produced
from primary oocytes via meiosis
meiosis produces cells that
-have half the # of chromosomes found in the original parent cell
-are genetically different from the parent cell and each other
why is the number of chromosomes halved
-to prevent mutations
-to keep number of chromosomes constant between all generations
-or else chromosomes double each generation
what are homologous pairs
-chromosome pair that have the same genes (chromosome one of mom with chromosome one of dad)
-not identical (because of alleles) but similar
what are alleles
alternative versions of a gene
what do alleles control
they control the same character but do not necessarily contain the same genetic info
what is the goal of meiosis
to convert diploid parent cells to haploid sex cells
how does the duration of mitosis compared to the duration of meiosis
mitosis takes around 12-24 hours
meiosis takes over 48 days depending on the species and cell type
what is the process of meiosis
-meiosis I (two daughter cells): prophase l metaphase l anaphase l telophase l cytokinesis
-meiosis II (4 daughter cells): prophase ll metaphase ll anaphase ll telophase ll cytokinesis
what is meiosis preceded by
interphase (same as mitosis)
-46 chromosomes but 92 chromatids
what’s the difference between mitotic prophase and meiosis prophase l
in mitosis the sister chromatids stay together
in meiosis l homologous pairs attach with another homologous pair (2Xs next to each other)
what are two pairs of homologous chromosomes next to each other called
tetrads
what is synapsis
two homologous chromosomes pair (2Xs) are held together tightly and crossing over happens
what holds the pairs together during synapsis
proteins
what is crossing over
exchange of genetic information between nonsister chromatids
when does crossing over happen
prophase I
what is the end result of crossing over
chromosomes will have the same number of genes but the sister chromatids are no longer identical
when can crossing over occur
can occur anytime on a chromosome during propahse I as agreat way to introduce variation
how is metaphase l difference than the mitotic metaphase
-in mitosis the sister chromatids line up single file
-in meiosis l chromosomes line up as homologous pairs (tetrads)
what happens in anaphase I
the homologous chromosomes pairs get separated (one X per side of cell)
- diploid into haploid
are telophase l and cytokinesis the same for meiosis l as for mitosis
yes
are the chromosomes replicated again between meiosis l and ll
no
how does meiosis ll compared to mitosis
almost the same except the sister chromatids are not identical because of the crossing over
where does cytokinesis occur
occurs in each cell produced by meiosis
how many cells are resulted from a parent oocyte
one ovum and three polar bodies
what are polar bodies
non functioning cells that aren’t big enough to continue the meiosis process
why is the one ovum the biggest one
because it has better chances of surviving past fertilization
has more nutrients to cell divide (to make zygote), can meet its metabolic needs
how does oogenisis and the ovarian cycle work
all eggs are made before birth, not fully developed which starts at puberty (paused until then)
what are the three ways of increasing genetic variation
-crossing over
-independent assortment of chromosomes (M1)
-random fertilization (conception)
what is the independent assortment of chromosomes
each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs in meiosis I
what is random fertilization
any sperm can fuse with any ovum
what is the evolutionary significance
-natural selection results in the accumulation of genetic variations favoured by environment
-certain combinations of alleles may work better
how are alleles connected to mutations
a mutation is the original source of different alleles
