Cell Division, Genetics, Molecular Biology

Front 1

Cell Cycle

Back 1

a process by which cells go through a sequence of stages from one division to the next

there are 2 types of cell division (mitosis and meiosis)

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Mitosis

Back 2

daughter cells have same # of chromosomes

Front 3

Meiosis

Back 3

daughter cells that have half as many chromosomes

produces sex cells, and has 2 sets of steps (interphase and division phase)

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Chromosomes

Back 4

clumps of DNA and protein

when DNA is clumped together with protein in a chromosome, its called chromatin

chromosomes can be condensed or uncondensed

during interphase, it's usually uncondensed
during M phase, it's usually condensed

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5 stages of Mitosis

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1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
5. Cytokinesis

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Sister Chromatids

Back 6

When chromosomes are duplicated they are attached by centromeres and called sister chromatids

One set of sister chromatids is still called 1 chromosome until it divides in M phase

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Interphase

Back 7

GI --> rapid growth, unduplicated chromosomes
S --> duplicating chromosomes (all DNA is duplicated)
G2 --> complete prep for cell division

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Prophase

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chromosomes shorten and thicken

centrioles move to opposite ends of cell

cell prepares for attachment of spindle fibres

Spindle fibres --> guides the chromosome movement

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Metaphase

Back 9

chromosomes line up in the middle of the cell

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Anaphase

Back 10

centrioles, using spindle fibres, pull apart sister chromatids

segments of chromatids break apart and then reattach

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Telophase

Back 11

spindle fibres dissolve

chromosomes lengthen

nuclear membranes

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Cytokinesis

Back 12

cytoplasm divides

in animal cells, cell is pinched

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Clones

Back 13

organisms with the same DNA

Front 14

Natural clones

Back 14

There are 2 types --> identical twins and asexual reproduction

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Asexual reproduction

Back 15

when a species reproduces without a partner and only involves mitosis

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Artificial cloning

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you can grow a whole individual from a single cell

first ever artificial animal clone was a frog

you must remove the nucleus from an egg and stick the nucleus from another cell (usually from a blastocyst)

Front 17

Artificial cloning, continued

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If you take DNA from a gastrula or anything further, it usually doesn't work because once you hit the gastrula stage is when the cells begin to specialize

more specialized cells have less ability to undergo mitosis

it is possible to use an adult cell as a nucleus donor

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Stem cells

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an undifferentiated cell from which any cell can arise

with appropriate signals, they'll differentiate into whatever specialized cell you want

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Telomeres

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every time you duplicate DNA, a little bit at the end of it is lost

DNA is on the end of the telomere, so you lose nothing important

eventually, your telomeres get so short that you can't undergo mitosis without losing important DNA

Front 20

Telomerase

Back 20

an enzyme that extends telomeres

cancer cells ignore messages to stop dividing

Front 21

Meiosis

Back 21

is a 2 stage cell division leading into 4 daughter cells with half as many chromosomes

in humans, there are 24 types of chromosomes (named X and Y)
we have 2 pairs of chromosomes 1-22, on X, then either an X or Y - totalling 46 chromosomes

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Homologus pairs

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the pairs of the same type of chromosomes

gametes are haploid (n)
adult cells are diploid (2n)
plants can be triploid (3n) or tetraploid (4n)

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Meiosis I

Back 23

consists of prophase I, metaphase I, anaphase I, telophase I

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Synapse

Back 24

the pairing up of Homologus pairs

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Anaphase I

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homologus pairs pulled apart instead of sister chromatids (2n --> n)

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Meiosis I and II

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between meiosis I and II, no duplication of DNA

meiosis II is identical in process to mitosis (except in mitosis you have 46 chromosomes and meiosis II you have 23 chromosomes)

in both meiosis II and mitosis you pull apart sister chromatids

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Crossing Over

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during meiosis I, homologus pairs group up (so 4 sister chromatids are intertwined)

at this point, they trade DNA to create entirely unique chromosomes

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Karyotype

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an arranged picture of chromosomes (arranged from biggest to smallest)

made by taking a cell and stopping mitosis at metaphase

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Spermatogenesis VS. Oogenesis

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both done via meiosis

spermatogenesis leads to the production of 4 sperm

oogenesis leads to 1 egg and 3 polar bodies

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Alternate Reproduction Strategies

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some animals alternate b/w sexual and asexual reproduction

some aphids use asexual reproduction all summer, then use sexual in the fall

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Life Stage I

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sporophyte (2n) produces spores (1n) via meiosis

spores grow into gametophytes

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Life Stage II

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gametophyte (1n) produces gametes (1n) via mitosis

2 gametes combine into a sporophyte

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Non disjunction

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a) in meiosis I --> homologus pairs don't separate

b) in mitosis or meiosis II --> sister chromatids don't seperate

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Human Gametogenesis

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if non disjunction occurs in MEISOSIS I, you'll get 2 gametes with an extra chromosome and 2 with a missing chromosome

If nondisjunction occurs in MITOSIS II, there will be an extra chromosome with 1 gamete missing and 2 normal gametes

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Human Gametogenesis continued

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if a gamete with 24 chromosomes combines with a normal gamete, you will have 3 homologus chromosomes called trisomy

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Monosomy

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missing a chromosome

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Trisomy 21

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missing an X chromosome

22 normal homologus pairs + 'X chromosome'

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Klinefetter Syndrome

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2 'X chromosomes' and a Y chromosome (XXY)