genetics unit one

meiosis

physical basis for mendelian genetics

most metazoans are _____

diploid

diploid

2 genomes/2 complete sets of genetic information, one set from each parent

prokaryotes

generally haploid (1 genome, can be many copies) genome generally on single DNA molecule

in eukaryotes, the genome is

distributed among many molecules “chromosomes”

chromosomes are

single DNA molecules wrapped around proteins

lower eukaryotes like yeast as well as plants

alternate haploid/diploid phases or generations

some eukaryotes are polyploid which means

they have more than two copies. can be evenploid or oddploid

oddploid organisms are generally _____

sterile

C is

DNA content

chromatids per chromosomal pair

in mitosis G2

1 cell that is 2N 4C

in mitosis

2 identical cells, both 2N 2C

in mitosis G1

2N 2C

in mitosis G2

2N 4C

two things done in meiosis

cut ploidy level in half

result in genetically different cells

transient diploid state results in

genetic differences

what do diploids have to do in meiosis

produce haploid cells with all chromosomes

in meiosis, one 2N cell produces

4 haploid cells

chromosome

portion of genome. DNA molecule plus associated proteins “chromatin”

sister chromatids

chemically identical portions of chromosome → after DNA replication

metacentric

centrosome in middle of chromosome, arms are same length

telocentric

centromere right at arm

aerocentric

one short arm one long arm

submetacentric

centromere near the middle

in G1, there is only

one chromatid per chromosome

chromosome arms

portions of the chromosome on opposite sides of the centromere

centromere

part of the chromosome to which kinetochore/spindle fibers attach

how does the centromere bind to the kinetochore?

DNA sequence at that location binds the proteins that make up the kinetochore

protein structure that binds to the DNA sequence of centromere

bind spindle, DNA, and motor proteins, spindle fibers are not retractable, the motor proteins walk

telomeres

the ends of the chromosomes

in interphase- bind to nuclear lamina to position chromosomes

homologous chromosome or homologue

chromosomes carrying the same genes, but not necessarily chemically identical

2 copies of same chromosome, maternal and paternal copies

ploidy

number of chromosome sets

homologues

same genes, but possibly slightly different forms of the gene→ alleles

diploid

each chromosome has a homologue

sex chromosomes excepted

meiosis N and C path

start with one 2N 4C cell → two 1N 2C cells → four 1N 1C

what happens in Anaphase I

homologous chromosomes separate into 2 daughter cells, each with complete genome

homologues are near each other but not _____

tightly associated

what holds homologues together to form bivalent

synaptonemal complex

bivalent

2 homologues put together

bivalents are called the

“four strand stage”

homologues exchange material called _____

chiasma

genetic consequence of exchanging material is _____

crossing over

sister chromatids are no longer identical after _____, still attached to the same centromere

crossing over

diakinesis

kinetochore generates force, bivalents are moved to center of cell

kinetochore contains _____ that generate pulling force

protein motors

what separates homologues

enzyme complexes, both proteases and topoisomerases separate homologues

independent assortment happens in

anaphase I

where is genetic diversity generated

exchange of chiasma in prophase I

homologue separation in anaphase I

when does chiasma occur

every meiosis, every chromosome

location of chiasmata is _____

random in drosophila

pseudorandom in humans

frequency of chiasmata is _____

proportional to distance

the further two genes are apart, the _____ a chiasma to form

more likely

at anaphase I the homologues are released by _____

enzymes