101: Lec 26

What is mitosis?

Division of a somatic cell to produce 2 identical daughter cells

What does mitosis make in uni and multicellular organisms?

Makes the whole unicellular thing, allows growth and repair in mulitcellular

What is the cell cycle for mitosis?

90% interphase (G1,S,G2), 10% mitotic phase

What happens in G1?

Metabolic activity and growth (e.g. proteins,organelles, mitochondria). Has unduplicated chromosomes

What happens in S?

Metabolic activity, growth, and DNA replication

What happens in G2?

Metabolic growth, activity, and prepping for cell division

How many chromatids do we have by the end of interphase?

92

How many centrosomes at the end of G2?

2

What do centrosomes do?

Organize microtubules to allow them to move cell contents to opposite poles of the cell

What happens in prophase?

Chromosomes start to condense, centrosomes start to move away from each other (they are making microtubules called spindles)

What happens in pro-metaphase?

Kinetochores form at the center of chromatids, microtubule spindles attach to them, and the nuclear membrane breaks down

What happens in metaphase?

Centrosomes at opposite poles, chromosomes line up on metaphase plate

What happens in anaphase and what is 1 fun fact about it?

Sister chromatids separate and move to either pole as kinetochore microtubules shorten, separating genetic material. shortest mitotic phase

What happens during telophase and cytokinesis?

Cell cleaves dividing chromosomes, nuclear membranes form, cytoplasm of parent cell divided between 2 new daughter cells

What is asexual reproduction and give an example?

Does not involve fusion of gametes or change in chromosome number e.g. hydra

What problem does meiosis solve and how?

Baby can’t get 92 chromosomes, so meiosis breaks parent chromosomes apart to make gametes (which also helps with genetic diversity)

What happens in meiosis I?

Separation of homologous chromosomes

What happens in prophase I?

Homologous chromosomes pair up and crossing over occurs between non-sister chromatids (which produces recombinant chromosomes)

How many crossing over events per chromosome?

1-3

What happens in metaphase I and anaphase I?

Chromosome pairs orientate randomly on the metaphase plate (independently). then in anaphase they are split to opposite poles

What happens in telophase I?

2 haploid cells form, each chromosome has 2 sister chromatids

Do we get crossing over or independent assortment in meiosis II?

No, because no longer any pairs of homologous chromosomes

What is independent assortment and when does it occur?

Each maternal and paternal homologue orients independently on the metaphase plate, occurs during metaphase I. 8.4million possible comibnations

What is crossing over and when does it occur?

The exchange of material between non-sister chromatids during prophase I. This produces recombinant chromosomes

What is random fertilization?

Any sperm can fertilize any egg (64 trillion combinations)

What is aneuploidy?

An abnormal number of chromosomes

What happens if we get non-disjunction at meiosis I?

2 gametes with an extra chromosome (n+1) and 2 gametes with 1 less chromosome (n-1)

What happens if we get non-disjunction at meiosis II?

2 gametes with either 1 too many or 1 too less chromosome, and 2 normal gametes

What is trisomic, monosomic, nullisomic, and polyploidy?