CELS 191 Lecture 15 Flashcards
what does G2 of interphase consist of in meiosis (this is the same as mitosis)
the nuclear envelope is still intact and the nucleolus is visible. two centrosomes have formed. chromosomes have been duplicated during S phase but have not yet condensed
what happens during meiosis one
the homologous pairs of chromosomes are separated
what occurs in prophase 1
the nuclear envelope breaks down, the chromosomes condense and the spindle forms. crossing over (exchange of DNA) between non-sister chromatids occurs at chiasmata (crossing over can’t occur too close to the centromere). each chromatid is now mix of DNA from each homologous chromosome
what occurs in metaphase 1
the chromosomes are attached to the kinetochore microtubules, at each centromere. each pair is lined up independently. paired homologous chromosomes have moved to the metaphase plate. the chiasmata line up on metaphase plate (not the centromeres, as in mitosis)
what occurs in anaphase 1
recombined homologous chromsomes seperate (disjoin). sister chromatids remain attached to each other (in anaphase of mitosis, sister chromatids seperate). the cell starts to elongate (non-kineochore microtubules extend), and each duplicated chromosome moves to the poles at opposite ends of the cell. the kinetochore microtubules contract and drag the chromosomes via the kinetochore
what occurs in telophase 1
duplicated chromosomes (the pairs of sister chromatids) reach poles at opposite ends of the cell. the spindle disappears and the nuclear envelope reforms
what occurs in cytokinesis of meiosis 1
in animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two. in plant cells a cell plate forms. cytoplasm divides, resulting in two haploid cells. haploid because only half the genetic information is in each new cell. cells (and sister chromatids) are genetically different due to crossing over
what occurs during meiosis 2
sister chromatids are separated
what occurs during prophase 2
the spindle forms as the centromeres duplicate and move to opposite poles. kinetochore microtubules attach to each duplicated chromosome at the centromere (via kinetochore proteins). each duplicated chromosome is still composed of two chromatids attached at centromeres
what occurs in metaphase 2
the duplicated chromosomes align at the metaphase plate. the centromeres lie on the metaphase plate
what occurs during anaphase 2
sister chromatids disjoin at the centromere. each chromatid becomes an independent daughter chromosome. daughter chromosomes move towards opposite poles as their kite chore mircotubules shorted. the non-kinetochore microtubules lengthen, and the cell elongates
what occurs during telophase 2 and cytokinesis
two daughter nuclei (with nuclear envelope) form in the cell. the meiotic division of one parent cell produces four daughter cells, each with a haploid set of (unduplicated) chromosomes. the four daughter cells are genetically distinct from one another and from the parent cell
out of meiosis 1, meiosis 2 and mitosis, which processes do the chromosomes align independently
mitosis and meiosis 2 - in meiosis 1 homologous chromosomes synapse
out of meiosis 1, meiosis 2 and mitosis, which processes require chiasmata
meiosis 1 only
out of meiosis 1, meiosis 2 and mitosis, which processes do centromeres line up on the metaphase plate
mitosis and meiosis 2 only - in meiosis 1 chiasmata line up on the metaphase plate
out of meiosis 1, meiosis 2 and mitosis, which processes involve chromatids disjoining
mitosis and meiosis 2 - in meiosis 1 chromosomes disjoin
asexual reproduction outperforms sexual reproduction every time so why do organisms choose to reproduce sexually
because genetic diversity allows selective responses for example to
spatially variable environments
changing environments
sib-sib competition
how does sexual reproduction produce genetic diversity
independent assortment of chromosomes
crossing over
random fertilisation of gametes
what is independent assortment
independent assortment states that during gamete formation, the alleles of different genes separate independently of one another, meaning the inheritance of one trait doesn’t influence the inheritance of another.
