Chapter 2 - Chromosomes and Cellular Reproduction

prokaryotic cells major features

No nucleus

divide quickly

DNA in physical in contact with ribosomes

prokaryotic reproduction

binary fission

only 1 origin of replication

very quick

eukaryotic cells main features

have nucleus

DNA is in nucleus

DNA is converted to RNA to leave the nucleus

slower cell division

ALOT of DNA

haploid number

number of types of chromosomes in a cell (n)

eg: n = 23 in humans

ploidy

number of each type of chromosome

diploid, haploid, triploid, etc.

diploid

2n

two copies of each type of chromosome

somatic cells

haploid

n

one copy of each type of chromosome

gametes

homologous pairs / homologs

two copies of each type of chromosome are identical

chromosomes that have the same genes in the same positions

alleles

different variations of one gene

locus

location of a genes on a chromsome

centromere

where spindle fibers attach to chromosomes

telomeres

the ends of linear chromosomes

help maintain chromosomes stability

sister chromatids

two identical DNA molecules after replication

mitosis

cell cycle

continuous division

makes identical copies

increases number of cells

meiosis

sexual reproduction

makes gametes

phases of cell cyles

Interphase → G0, G1, S, G2

M-Phase → mitosis, cytokinesis

interphase

G0, G1, S, G2

DNA replication and cell growth

M-phase purpose

mitosis and cytokinesis

nuclear and cytoplasmic division, chromosomes separation and cell division

G0

non-diving phase

cell may enter

‘time out’

G1

cell growth

preparation for division

centrosome division

G1/S checkpoint

checks of replication machinery

checks for DNA damage

commitment to division

S

DNA replication

G2

preparation and growth for division

organelle replication

G2/M checkpoint

ensures cell has everything it needs for mitosis

checks for DNA damage

M-phase sections

prophase

prometaphase

metaphase

anaphase

telophase

cytokinesis

prophase

chromosomes condense

centrosomes move toward poles of cells

2 chromatids per chromosome

mitotic spindles form

prometaphase

nuclear envelope breaks down

spindle fibers attach to chromosomes

metaphase

chromosomes line up along metaphase plate

spindle assembly + M checkpoint

anaphase

sister chromatids separate

separase breaks down cohesin

telophase

chromosomes decondense

cleavage furrow forms

nuclear envelope reforms

cytokinesis

cytoplasm division

number of chromosomes + DNA molecules in G1

chromosomes = 4

DNA = 4

number of chromosomes + DNA molecules in S

chromosomes = 4

DNA = 4→8

number of chromosomes + DNA molecules in G2

chromosomes = 4

DNA = 8

number of chromosomes + DNA molecules in prophase

chroms = 4

DNA = 8

number of chromosomes + DNA molecules in metaphase

chrom = 4

DNA = 8

number of chromosomes + DNA molecules in anaphase

chrom = 8

DNA = 8

number of chromosomes + DNA molecules in telophase

chrom = 4

DNA = 4

fertilization

fusion of haploid gametes

meiosis 1

separation of homologous pairs

reduction in chromosomes number by half

Reduction Division

prophase 1

homologous chromosomes pair

crossing over occurs between non-sister chromatids

metaphase 1

homologous pairs line up along metaphase plate

random assignment

random assignment

homologous pairs align randomly

genetic variation

anaphase 1

homologous chromosomes separate

sister chromatids stay together

shugosin prevents cohesin near the centromeres from being degraded by separase

telophase 1 + cytokinesis

cytoplasm divides

interkinesis

between meiosis 1 and 2

nuclear membrane reforms

spindle fibers disappear

chromsomes decondense

centrosomes dupplicate

meiosis 2

separation of sister chromatids

maintains chromosomes number

like mitosis

Equational Division

prophase 2

chromosomes recondense

nuclear membrane breaks down

spindles fibers reform

metaphase 2

individual chromosomes line up along equatorial plate (perpendicular to metaphase plate)

anaphase 2

sister chromatids separate

shugosin and all of cohesin is degraded

telophase 2 + cytokinesis

cytoplasm divides

produces 4 genetically distinct daughter cells with half the number of chromosomes

crossing over

shuffles alleles between the same types of chromosomes → creates new combinations

in prophase 1

between non-sister chromatids