Cell Cycle

describe what DNA content is (C) and in a normal haploid cell, what is it in g?

how many helices make up 1 chromosome (if it has a centromere holding 2 together it is 2C), 3.5E-12 g

compare euchromatin and heterochromatin

Eu- active, loosely packed, stains lightly

Hetero - inactive, tightly bound, stains dark

what is constitutive heterochromatin

always inactive and has lots of repeat sequences so if a lysogenic virus comes in and tries to put its DNA in your DNA, it puts it in an inactive region and the viral DNA does not get read

describe all of the stages of the cell cycle

Gº - resting, not actively cycling

G1 - preparing to duplicate DNA

S - DNA synthesis (still 46 chs (2n) but not its 2C)

G2 - cells are preparing to separate

M - mitosis

describe the 3 checkpoints in the cell cycle

G1 - cell size, nutrients, growth factors, DNA damage

G2 - cell size, did DNA replicate properly

M/spindle assembly - are the spindle properly attached to the centromeres

difference between centromere and centrosome

centromere hold chromatids together, separates q and p arm, and act as attachment site for spindle fibres

centrosomes are made of centrioles, they go to the poles, make spindle fibres with alpha and beta tubulin

6 differences between meiosis and mitosis

location: mitosis is in all tissues, meiosis is in gametes

mitosis makes diploid cells, meiosis makes haploid

mitosis duplicates and divides once, meiosis duplicates once and divides twice

mitosis is fast, meiosis is slow

no recombination in mitosis but yes in meiosis

mitosis leads to genetically identical but not in meiosis because of recombination and independent assortment

describe the flow of egg development

oogonium undergoes growth and differentiation —> primary oocyte (2n) undergoes meiosis 1 —> secondary oocyte (n) + polar body (cytoplasm divided unequally) undergoes meiosis 2 —> mature egg and polar body

describe the flow of sperm development

spermatogonium does growth and differentiation and division —> primary spermatocyte (2n) does meiosis 1 and 2 —> secondary spermatocyte (n) —> 4 spermatids

what are the possible combinations of recombination

46 chromosomes so 2^(23)

What did Dr. Hayflick discover

cells have a finite lifespan in culture, “immortal” cells are stem cells and cancer cells

function of telomeres

maintain DNA integrity, help DNA replication finish without damaging actual DNA, and help orient chromosomes into the nucleus

what is a common approach in chromosomal staining and why do we do it

G-banding with giesma stain under a light microscope to help identify abnormalities

how might you track genes to see if they do recombination, or to see if there is an abnormality

add fluorescent probes or paint the chromosome

describe mixoploidy and 2 types

2 or more genetically distinct lineages in 1 person

mosaicism - abnormality within the same zygote

chimerism - eats the twin and gets its DNA

what is a mosaic

different tissues can have different sets of chromosomes

what is a constitutional abnormality

abnormal egg, sperm, or fertilization

can be 2 sperm, 1 egg or vice versa (triploidy)

can be DNA duplication but no division so its 4n (tetraploidy)

describe the Philadelphia chromosome

translocation between ch 9 and 22, occurs in 95% of chronic myeloid leukaemia patients which activates a kinase that is targeted by imantinib (small molecule inhibitor), ch 22 becomes the Philadelphia chromosome

describe robertsonian translocations

translocation where the p arm is very very small, and it swaps p arms with something else (centric), now one chromosome has 2 centromeres and one is acentric. acentric is lost in mitosis, but the dicentric one, there centromeres are so close they essentially function as 1 so it is stable (leads to 45 chromosomes instead of 46)

what is nullisomy

lacking a pair of homologs (lethal before implantation)

what is monosomy

lacking 1 chromosome (lethal during embryonic development)