Session 1: Chromosomes and Mitosis

chromosome

contains one long molecule of duplex (double stranded) DNA molecule

each chromosome contains

many genes

genome of an organism

is one full set of chromosome haploid

haploid

n, one half of diploid 2n

chromosome and chromatid

double-stranded DNA molecules

use the term chromatid specifically

when referring to DNA during the cell cycle to indicate the state of a chromosome as either unreplicated (one chromatid) or replicated (two chromatids).

The two chromatids of a chromosome that are present after DNA replication are called

sisters

Two different chromosomes that have the same gene content, but are inherited from different parents are

homologs

Genetic information is stored in

chromosomes

chromosomes are located in

nucleus

genetic information is stored as discrete instructions called

genes

genes

fundamental unit of information, all information to be what we are stored in genes

diff versions of genes

alleles

DNA markers are used to

identify particular regions along the DNA in chromosomes

all chromosomes make up

genome

genome is

all of the dna we can account for, not just the genes, all of dna

what is unique about genomes

is number of genes in a species

• diff # of chromosomes

• diff # of genes

these what make genomes unique

humans have how many chromosomes

46 chromosomes, 2 sets of 23 chromosomes

23 pairs of human chromosomes (this IS the genome, 23 chromosomes)

23 is 1 single set of chromosomes

size of human genome

3 × 10^9 base pairs (3 billion)/ 23 chromosomes

23 chromosomes

haploid (half of chromosome complement)

it is the genome though, all the unique genes, all of the DNA in one set of chromosomes

46 chromosomes

2 sets of 23 chromosomes

1 way to visualize chromosomes is through

karyotype, mitotic spread of chromosomes

we are diploid meaning

we have 2 sets of chromosomes, two copies of each chromosomes

diploid gets

1 set of chromosomes from female parent

1 set of chromosomes from male parent

homologous chromosomes

• carry information for the same proteins or same RNAs, carrying the same traits and characters

• one from dad, one from mom

locus

location of a gene, physical location

multiple of locus is loci

gene variants are called

alleles

there are different versions of a gene called

alleles

allele difference can be difference in

molecular makeup OR some visible phenotypic consequence

phenotype

• an observable characteristic or trait

• product of gene expression

• ex: eye color, hair color

common phenotype in population

is wild type allele

rare phenotype in population

is mutant

disease causing allele vs normal allele

normal = wild type

mutant, non-functional, disease causing = mutant

genoype

how alleles present at a locus are described

indicates what alleles are found in the chromosomes

dominant allele generally

capital letter

recessive allele

lowercase letter

recessive many times is mutant, but not always

2 diff alleles for a gene

person is heterozygous for this gene

2 same alleles for a gene

homozygous (both cap or both lowercase)

homologous chromosomes are the same in the sense that

they are carrying information for the same traits

• might have identical information

• or different information (heterozygous)

one from each parent doesn’t have to be identifical

telomeres

• ends of the chromosomes

• unique replication and structure

• minimize degradation

chromosome short arm

p arm

chromosome long arm

q arm

in the center constriction point of chromosome

centromere

off from middle to get short and long arm

centromeres are how

after replicaiton duplicated chromosomes are held together

two chromatids held together by centromere

chromosomes are necessary for

proper replication and segregation of the genome

organizes genes for proper expression

chromosome transmission

how chromosomes get passed on from 1 generation to the next

cell division

cytokinesis

what happens in cyotkinesis

• divvying up all organelles and genetic info

• splitting in 2

Division of chromosomes

mitosis

process of cell division (cycle) is controlled by

cell cycle

from mitosis through dna rep back thru mitosis,

1 round of cell division and segregation of DNA

Order of chromosome rep cycle

G1, S, G2, M

G1

• End of mitosis to the beginning of DNA replication

• Gap 1 before chromosome replication

S

Synthesis—DNA replication

when and where chromosomes get duplicated

making identical copy of DNA

chromosomes have 2 copies each held together at centromere, have 2 chromatids

G2

Gap 2 preparation for mitosis

M

mitotic phase

mitosis chhromatid separation

chromosomes line up and divide

get equal copy of the genome in the daughter cells

get full copy of the complement of chromosomes in daughter cells

steps of mitotic phase

PMAT

prophase

prometaphase

metaphase

anaphase

telophase

chromosome most of the time

are not in X shape

most of the time thin and thready like a ball of yarn, can’t see individual chromosomes

chromosome in x shape only in

M phase when chromosomes condense and wind up tightly and become visible

karotypes

only seen during M phase

help visualize big rearrangements like duplications and translocations

chromatid

only used when talking about chromosome replication cycle*

how we refer to whether a chromosome has one double stranded molecule of DNA or two double stranded molecules of DNA held together by centromere
Chromatid is one double stranded DNA molecule

sister chromatids

products of DNA replication

two chromatids that are held together by the centromere

two identical double stranded dna bond together by centromere

homologs

the matching chromosomes of a diploid cell that are derived from different parents

Prophase

Chromatids are Paired

chromosomes condense and get nice and tight, see x shape

Prometaphase

• centrosomes move to poles

• nuclear envelope dissolve

• centrosomes send out microtubles and spindle fiber that grab chromosomes

Metaphase

Chromosomes align in Middle of cell

spindle fibers (type of microtubles) pull chromosomes to the equator of the cell during metaphase aka metaphase plate

Anaphase

Chromosomes pull Apart

spindle fibers shorten, pull sister chromatids apart at the centromere

• back to one chromatid chromosome

Telophase

Result= Two chromosome sets, Two daughter cells

spindle fibers go away, the chromosomes decondense and new nuclear envelope forms

Cytokinesis

finished pinching off membranes, two individual daughter cells

Goal of mitosis

• Make clonal sets of chromosomes

• duplicate all chromosomes to produce two daughter cells, each with a full genetic set, each with a full genetic complement

mitosis happens in what type of cells

somatic cells

Goal of meiosis

• Make gametes, generate diversity

• Rare form of cell division goal is to reduce the number of chromosomes by two, cut everything in half to make gametes

• a complete set of genome but not two book copies