mitosis and meiosis Flashcards
what type of cells are produced through meiosis
-gametes
-egg or sperm
-haploid
what is a haploid cell
a cell that has one copy of each gene
where does meiosis occur
gonads (testes or ovaries)
what is it called when meiosis occurs in males
spermatogenesis
what is it called when meiosis occurs in females
oogenesis
what happens in interphase of meiosis
-G1 cell grows and carries out life processes
-S chromatin replicates and is organized into chromosomes
-G2 Cell prepares for cell division
what is meiosis I
-reduces the chromosome number by half
-involves homologous chromosomes
what happens in prophase I
-it is the longest and most complex phase
-nuclear membrane dissolves and chromosomes condense
-centrioles make spindle fibres which are attached to to centromeres
-synapsis occurs
-crossing over occurs
what is synapsis
process by which homologous chromosomes come together to form a tetrad
what is a tetrad
consists of two chromosomes of 4 chromatids (sister and non sister) joined together
what are homologous chromosomes
-pair of chromosomes (maternal and paternal) that are similar in shape and size
-homologous pairs (tetrads) carry genes controlling the same inherited traits
-humans have 23 pairs of homologous chromosomes
-22 pairs of autosomes
-1 pair of sex chromosomes (XX, XY)
what is crossing over
-leads to variation
-may occur between non sister chromatids
-segments of non sister chromatids break and reattach to the other chromatid
what happens in metaphase I
-shortest phase
-tetrads align on the equator
-independent assortment occurs - orientation of homologous pairs is random (allows for more variation)
what happens in anaphase I
-homologous pairs separate and move towards poles
-sister chromatids remain attached at their centromeres
what happens in telophase I
-each pole now has haploid set of chromosomes
-two new nuclear membranes form
-spindle fibres dissolve and their centrioles duplicate
-cytokinesis occurs and two haploid daughter cells are formed
what does not happen in meiosis II
interphase because there is no more DNA replication to be done
what happens in prophase II
-DNA condenses into chromosomes
-nuclear membranes disappear
-centrioles move to the poles of the cell
-spindle fibres form
-same as prophase is mitosis
what happens in metaphase II
-chromosomes line up in the middle of the cell
-spindle fibres push them there
-same as metaphase in mitosis
what happens in anaphase II
-centromeres divide and the sister chromatids separate
-sister chromatids are pulled by spindle fibres to opposite sides of the cell
-same as anaphase in mitosis
what happens in telophase II
-centrioles duplicate and spindle fibres disappear
-4 new nuclear membranes form
-cytokinesis occurs
-produces 4 genetically unique haploid daughter cells
-same as telophase in mitosis
what does spermatogenesis produce
-4 haploid spedm for every one diploid cell
what does spermatogenesis produce
-4 haploid spedm for every one diploid cell
what does oogenesis produce
-only 1 mature haploid egg cell and 3 polar bodies for everyone 1 diploid cell
-the polar bodies will be broken down and reabsorbed
-polar bodies donate their nutrients to the egg because after fertilization the zygote doesn’t implant for 7 days
what is fertilization
the fusion of a sperm and egg to form a zygote
what is a zygote
a fertilized egg
what is no disjunction
-failure of chromosomes to separate and segregate into daughter cells
-may occur during meiosis I or meiosis II
abnormal number of chromosomes may result
where does non disjunction occur in meiosis I
during anaphase the homologous chromsomes both go to one cell
what does nondisjunction in meiosis I result in
two diatomic gametes and two nullisomic gametes
where does nondisjunction occur during meiosis II
in anaphase two one pair of sister chromatids fail to separate
what does nondisjunction in meiosis II result in
one disomic gamete, one nullisomic gamete, and two monosomic gametes
