Lecture 13 Flashcards
How do single cell organisms reproduce
Binary Fission (asexual reproduction)
Why is Meiosis important in preventing gametes being doubled
as mitosis would increase 2n to 4n
need meiosis to halve chromosome in gametes (n) to diploid number in 2n
What happens in Meiosis
homologous chromosomes from interphase seperate= haploid cells with duplicated chromosomes
What Happens in Meiosis II
Sister Chromatids seperate= haploid cells with unduplicated chromosomes
What happens in Prophase I
Centrosome movement, spindle formation, nuclear envelope breakdown (mitosis prophase)
Chromosomes pairs with homologs
crossing over
later in stage microtubules attach to two kinetochores move to the metaphase plate
What is crossing over
occurs in Prophase I
DNA molecules of non-sister chromatids are broken and rejoined to each other
x shaped regions (chiasmata)
What happens in Metaphase I
Pairs arranged at the metaphase plate, one chromosome in pair faces each pole
Both chromatids attached to spindle from opposite pole
What happens in Anaphase I
Protein breakdown of cohesion allows homolog to separate
homologs moved towards opposite poles
sister chromatid cohesion persists at the centromere, chromatids move as a unit to the same pole
What happens in Telophase and Cytokinesis I
Each cell has a haploid set of chromosomes, two sister chromatids, regions of non-sister DNA (crossed over)
Cytokinesis occurs
no duplication
What happens in Prophase II
spindle forms
late prophase, two chromatid chromosomes move toward metaphase plate
What happens in metaphase II
Chromosomes are positioned at the metaphase plate
sister chromatids not genetically identical (crossing over)
Attached to microtubules from opposite poles
What happens in Anaphase II
cohesive protein breakdown separates chromatids, move towards opposite poles
Telophase and Cytokinesis
Nuclei form, chromosomes are not condensed,
cytokinesis
One parent cell- 4 genetically different cells
What are the differences between Mitosis and Meiosis I
Mitosis chromosomes align independently no chiasmata centromeres on the metaphase plate chromatids disjoin 2n-2n
Meiosis I Homologous chromosomes synapse Chiasmata Chiasmata on metaphase plate Chromosomes disjoin 2n-n
How does genetic diversity remain in a population
independent assortment of chromosomes
crossing over
random fertilization of gametes
