Biology Unit 2, Part 1: genes, cell division

Genetics

the stuff and study of heredity

Gene

unit of heritable information, carries information across generations about phenotypic feature, sequence of DNA that encodes a gene product

Reproduction problems to be solved

transfer information and apportionment of biological materials

Asexual reproduction

offspring are clone of parent, all prokaryotes (binary fission) and many eukaryotes (mitosis)

Sexual reproduction

two parents combine genes (meiosis), leads to recombination, only in eukaryotes

Mitosis

genetic material (chromosomes) is equally partitioned into two daughter cells (eukaryotes)

Binary fission

in prokaryotes, proteins bind to origin site of replication (ori) to direct chromosomes to poles, analogous to mitosis

Centrosome

tubular proteins that regulate movement of nucleus material

Centromere

where chromatids join at the middle

Mitotic spindle

is involved in creating force needed for chromosome movement, made of microtubules

Interphase

Prep phase for cell before mitosis, DNA loose and not compact

Interphase stages

G1: cell grows larger makes new proteins, copies organelles. S-phase: copies DNA = sister chromatids, which are attached to same DNA molecule by proteins and centrosomes duplicate

4 Mitosis stages

Prophase, metaphase, anaphase, telophase

Prophase stages

Early prophase: chromosomes condense, mitotic spindle forms from centrosome, centrosomes begin to migrate to poles of cell, nucleoli disappear. Mid-prophase: chromosomes fully condensed, centrosomes complete migration to poles, nuclear envelope begins to degrade, spindle fibers enter nuclear area from pole, kinetochores form at centromeres

Prometaphase

nuclear envelope degrades completely, spindle fibers begin to attach at kinetochores, sister chromatids attach to opposite poles

Metaphase

spindle fibers attached to centromere at kinetochore, all sister chromatids attached to opposite poles, chromosomes migrate to center plane of cell “metaphase plate”

Anaphase

Protein bond between sister chromatids degrade, sister chromatids separate, poles move further apart as non-kinetochore spindle fibers lengthen

Unreplicated chromosomes

term for the sister chromatids after they have been pulled apart in anaphase

Telophase

non-kinetochore spindle fibers continue to elongate cell, nuclear envelopes begin to form at poles, chromosomes de-condense back into chromatin, nucleoli re-form, cytokinesis begins

Cytokinesis

Animals: pinch inward to form furrow. Plants: cell plate forms between. Requires energy, involves golgi apparatus (makes vesicles to transport microtubules for cell plate), distibrutes organelles.

46 chromosomes

number of chromosomes humans have

Sexual reproduction in animals

free-living stage is diploid, gametes formed by meiosis, haploid cells merge genomes to form diploid zygote

Sexual reproduction in plants

Diploid sporophyte form haploid spores by meiosis, spores form gametophyte by mitosis, gametophyte forms gametes by mitosis, gametes merge to form zygote

Sexual reproduction in fungi

free-living organism is haploid, gametes formed by mitosis, gametes merge to form diploid zygote, zygote undergoes meiosis to form haploid cells

Meiosis overview

Splits a diploid cell twice (I,II) to create four unique haploid cells. Both rounds follow the PMAT (Prophase, Metaphase, Anaphase, Telophase) steps.

Meiosis I

Seperating homologous chromosomes,

Early prophase I

Chromosomes condense and pair up with their matching partners (homologous chromosomes) (homologs form tetrad).

Late prophase I

Chromosomes perform crossing-over (form chiasmata), swapping chunks of DNA to create brand-new genetic combinations (occurs at chiasma), spindles form and attach to kinetochores

Metaphase I

chromosomes line up in middle, spindles from poles attach to the different chromosome of each pair,

Anaphase I

homologous chromosomes seperate and move along spindle fibers toward pole, sister chromatids remain attached at centromeres

Telophase I and cytokineses

homologous chromosomes reach opposite poles, each pole has complete haploid complement of chromosomes, each chromosome consists of two sister chromatids

Prophase II

spindle forms, chromosomes move toward metaphase plate (middle)

Metaphase II

Chromosomes reach metaphase plate, kinetochores of sister chromatids attach to spindle fibers from opposite poles

Anaphase II

centromeres of sister chromatids seperate, sister chromatids move toward opposite poles

Telophase II and cytokineses

mechanism same, produces four haploid daughter cells

Cyclin-dependent kinases

specialized enzymes that respond to cell-external signals (growth factors), which act on cell-internal signals