BIO 111 Week 10

origins of genetic variation

crossing over (prophase I) independent assortment of chromosomes (metaphase I) random fertilization

most checkpoints use a system of kinases called"

cyclin-dependent kinases

cleavage furrow

shallow groove in the cell surface

genes

units of heredity and are made up of segments of DNA genes are passed to the next generation during Meiosis each gene has a specific location called a locus on a certain chromosome haves information for making molecules of RNA and protein that the cell needs

cell cycle control system

-cell division is tightly regulated cell cycle control system: cyclically operating set of molecules a molecular "timer" with checkpoints to ensure the cell is ready to proceed past crucial points

cytokinesis is concurrent with telophase

-formally not part of mitosis -separate phase in M phase -final and complete separation into two autonomous cells- meaning that these two cells can survive on their own to survive

Cell cycle clock:

cyclins and cyclin dependent kinases

cleavage

pinching of plasma membrane

gametes:

2 different cell (sperm and egg) egg: contributes bulk of of cytoplasmic contents toward the zygote and the new organism sperm: only about contributing it's genetic content-lacks any other features

Meiosis I, Telophase and Cytokinesis

2 haploid cells form each chromosome still exist as sister chromatid

sister chromosome

3 identical copies is made up of DNA wound around histonprotein each strand coils up into a tight hico fiber

karyotype

a complete set of chromosomes in a species or individual homologous pair X shaped also a test to detect chromosomal abnormalities

Difference between anaphase I and anaphase II

anaphase I: the two chromosomes of each tetrad separate and start to move toward opposite poles of the cell. The sister chromatids remain attached at their centromeres and move together toward the poles anaphase II: the centromeres separate, and the two chromatids of each chromosome-now called daughter chromosomes-move separately to opposite poles on the spindle

Autosomes

any chromosome that is not a sex chromosome ex: 22 pairs in humans -each pair is homologous

Meiosis II the same as mitosis

begins with a haploid cell ***prophase II: no crossing over metaphase II: sister chromatids are no longer identical -chromosomes align on the metaphase plate anaphase II: sister chromatids are separated -back to being individual chromosomes -as microtubules shorten, they will pull there now individual chromosomes to the opposing pulls to the cell telophase II: 4 daughter cells form -no longer sister chromatids -nuclei form at opposite pulls of each of each dividing cell cytokinesis: splits the cells apart

prometaphase

between prophase and metaphase chromosomes are in complete condensed phased

metaphase

cell checks to make sure chromosomes are evenly distributed across a imaginary plane called the metaphase plate when cell is ready to divide, each chromosome is connected at the kinetochore to the mitotic spindle on the opposite side nuclear envelope completely degrades mitotic spindles are on opposite ends of the pull and is ready to separate the chromosomes

metaphase checkpoint

cell receive a molecular signal when senses each chromosome is attached to each spindle pole cell receive stop signal when any chromosomes are not attached cell receives go-ahead signal when all chromosomes are attached separase- enzyme that degrades proteins at the centromere initiates separation of chromatids and anaphase begins non-attached MTs elongate to overlap with those from opposite spindle poles motors link them together and push them apart while the MTs continue to elongate continually pushes the centrosomes apart, elongating the cell

cytokinesis in plant cells

cell wall cannot be pinched like the plasma membrane vesicles derived from golgi coalesce into a cell plate -vesicles fuse until either end of the cell, separating the two cytoplasm's -material inside the vesicles become the new cell wall

checkpoints

cellular conditions must be met before the cell progresses to the next phase control system senses these conditions and signals the cell to progress when conditions meet

G2 of interphase

centrosomes (with centriole pairs) nucleus nuclear enveolope plasma membrane

Meiosis I, Metaphase I

chromosomes align along plate by homologous pairs independent assortment

Steps for mitosis to occur

chromosomes need to condense chromosomes needs to be accurately segregated into new daughter nuclei w -only one copy of each chromosome physical separation nuclear envelope needs to be disassemble and new ones reassembled

cytokinesis in animal cells

cleavage cleavage furrow process is driven by a contractile ring of actin microfilaments -ring is bound to inner surface of plasma membrane so as the ring contracts, the cell gets pinched in the middle

locus

each gene has a specific location called a locus on a certain chromosome

mitotic spindle forms during:

early mitosis and quickly degraded as soon as it's done it's job

prophase

early mitotic spindle aster centromere two sister chromatids of one chromosome

Goal of Reproduction:

ensure propagation of the species

sister chromatids

exact copies genes are in the same place

microtubules

hollow tubes tubulin, a dimer consisting of an a-tubulin and a b-tubulin maintenance of cell shape; cell motility; chromosome movements in cell division; organelle movements existing microtubules get disassembled during prophase to provide recycles tubulin monomers

diploid is 2n

homologous chromosomes humans diploid 3 = 2(23)=46

Meiosis I, Anaphase I

homologous pairs separate from each other sister chromatids remain attached

synapsis: crossing over

homolous chromosomes loosely associate with each other break DNA complex forms to hold homologs together "synaptonemal" breaks sealed by joining ends of non-sister chromatids forms sister chromatids that are not exact copies

Ploidy:

how many chromosomes should we expect to find in the cell of an organism n=number of chromosomes

mitotic spindle is responsible for:

insuring that each daughter cell will inherit one copy and it does the physical separation of the chromatids

difference between metaphase I and metaphase II:

metaphase I: the homologous pairs of chromosomes become aligned in the middle of the cell and are attached to the now fully formed meiotic spindle. each homologue consists of two sister chromatids, so there are, in total, four chromosomes metaphase II: each chromosome becomes aligned in the middle of the cell, much as the chromosomes do in mitosis, and is attached to the now fully formed spindle. Each chromosome consists of one pair of sister chromatids, so there are, in total, two chromosomes.

mitotic spindle is made of:

microtubules

mitotic spindle at metaphase:

microtubules attach to chromosome centromere forming kinetochores each sister chromatid is attached to a bundle of microtubules microtubules attach to chromosome centromere forming kinetochores each sister chromatid is attached to a bundle of microtubules sister chromatids must be attached to bundle from opposite spindle poles

haploid state

n value not duplicated no sister chromosomes not homologous chromosomes humans haploid# = 23 ex: sperm and egg

Asexual reproduction

offspring originate from a single parent all are genetically identical to the parent clones great if the organism is well adapted

meiosis I, Prophase I:

prophase I: -duplicated, homologous chromosomes pair up -crossing over happens here (snypsis) -homologous chromosomes pair up

difference between prophase I and prophase II

prophase I: the duplicated homologous chromosomes paur up, and crossing-over occurs. At this point each homologous chromosome pair is visible as a tetrad, a tight grouping of four chromatids, two of them sisters and two of them non-sisters. The sites of crossing-over are seen as crisscrossed chromatids and are call chiasmata. Prophase II: While chromosomes duplication took place prior to meiosis I, no new chromosome replication occurs before meiosis II. In prophase II, then, the chromosomes are seen as pairs of sister chromatids attached by their centromeres.

telophase and cytokinesis

reconstruct nuclear envelope chromosomes decondense back into chromatin nucleoli reform overlaps with the process called cytokinesis telophase and cytokinesis happen at the same time

Sexual reproduction

requires 2 parents to create offspring fusion of gametes (sperm and egg) creates a zygote zygote: very first cell of our new offspring offspring are generically different from parents great for increasing survival rates

anaphase

separation of sister chromatids from the metaphase plate all id does is pull cells apart shortest stage microtubules are not attached to chromosomse. protein motors act to push the two centrosomes apart and elongate the cell this leads to chromosomes ending up on one end associated with the opposing centrosome

Difference between telophase I and telophase II

telophase I: the homologous chromosome pairs complete their migration to the two opposite poles. Now a set of chromosome still having two chromatids telophase II: the two chromatids of each chromosome have separated during anaphase II to produce individual chromosomes, each of a single chromatid, and that is what is seen in each nuclear area of telophase II.

Sex chromosomes

the pair of chromosomes that determine biological sex of an organism X or Y these are only partially homologous X: larger than Y, general human development the Y is smaller and has different genes

meiosis summary:

two rounds of cell division produces haploid daughter cells new cells are not genetical identical to each other used to make gametes

4 major meiotic differences from mitosis

two rounds of division in order to form final daughter cells four daughter cells instead of two cells are deduced to haploid cell. (value of n) genetic variability introduced by crossing over

duplicated homologous chromosomes

two sister chromatids that are different colors