4 subdisciplines of genetics

1. Mendelian Genetics

2. Cytogenetics

3. Molecular biology/genetics

4. Population/Quantitative/Statistical Genetics

 genetics

the study of heredity and variation

heredity

cause of similarities between individuals

variation

cause of differences between individuals

gene

unit of inheritance transmitted from parent to progeny

genotype

genetic makeup of organism

phenotype

anything that can be perceived by the senses

allele

one member of 2 or more alternate forms of a gene occupying the same locus

locus

specific location of a gene on a chromosome

diploid

2 chromosomal sets

Gregor Mendel

father of genetics

 homozygote

diploid or polyploid with the same allele

heterozygote

diploid/polyploid with different alleles

dominant

in a pair of alleles, a member expresses in complete exclusion of the other member.

recessive

a member fails to express itself in the presence of dominant counterpart.

monohybrid cross

1 characteristic, 2 parents

dihybrid cross

2 traits, 2 parents

test cross

a cross between an individual of dominant phenotype with 1 individual of recessive phenotype.

why perform a test cross?

           -find out if it is homozygous dominant

           -linkage analysis

backcross

cross between progeny and parent

why do a backcross?

develop purebreds.

reciprocal cross

a pair of crosses in which the genotype of female and male parents in the first cross are reversed in the second cross.

why do a reciprocal cross?

find out if there is maternal inheritance

Mendelian principles

1. Principle of Dominance

2. Principle of Segregation

3. Principle of Independent Assortment

Principle of Dominance

in heterozygotes, one allele may mask the expression of the other allele.

Principle of Segregation

in heterozygotes, 2 different alleles segregate from each other during the formation of sex cells so that any one gamete receives one or the other allele.

Principle of Independent Assortment

the segregation of the members of a pair of alleles is independent of the segregation of other pairs during the process leading to the formation of the sex cell

gamete generation/possible combination

the number of different kinds of gametes that can be produced depends on the number of loci for which the individual is heterozygous.

Exceptions from Mendel's laws

1. Codominance

2. Incomplete Dominance

Codominance

the expression of both alleles in a heterozygote

(mixture of trait)

Incomplete Dominance

condition in heterozygotes where the phenotype is intermediate between the 2 homozygotes.

(blending)

3 major components in interphase nucleus

1. karyolymph

2.nucleolus

3. chromatin

karyolymph

clear nuclear sap containing protein

karyotype

picture of a chrmosomes organized by length in descending order; organized by centromere and bending pattern

p arm

short arm of sister chromatid

q arm

long arm of sister chromatid

what are the 4 features used to distinguish the morphology of a chromosome?

1. length

2. bending pattern

3. presence/absence of satellites

4. centromere location, relative arm length

name the 4 classifications of centromere location.

metacentric

submetacentric

acrocentric

telocentric

metacentric

centromere is central and arms are equal length

submetacentric

one arm is longer than the other

acrocentric

centromere is near one end; arms very unequal in length.

telocentric

centromere is terminal, no 2 arms

polyteny

lateral multiplicity

euchromatin

stain slightly or not at all

heterochromatin

stains darker

name the 3 types of chromosome bands.

C-Bands

Q-Bands

G-Bands

C-Bands

Constitutive heterochromatin (constant)

-always occur in particular space-- in proximity of telomere and centromere

Q-Bands

Quinacrine Mustard

bright orange/yellow, enhances G-Band, tends to be temporary

G-Band

Giesma dye Mixture

overcomes temporary effect of Q flourescence

The cell cycle

G₁ of cell cycle

organelles double in number, cell enlarges, some protein synthesis

S phase of cell cycle

DNA replication

G₂ phase of cell cycle

makes sure DNA properly replicated

protein synthesis- enzymes for cell division 

G₀ phase of cell cycle

rest stop/permanent arrest

What kind of cells are permanently arrested?

muscle cells and nerve cells

what are checkpoints and where are they in the cycle?

make sure everything was done correctly in the previous stage, repair damages.

at the end of G₁, end of G₂, and in the beginning of M.

what are the 4 substages of mitosis?

Prophase, Metaphase, Anaphase, Telophase

What happens in prophase?

-chromatin condenses, chromosomes are visible

-nuclear envelope disintegrates

-nucleases become mute

-nucleoli disappear

-pairs of centrioles begin moving to opposite poles

-spindle apparatus begins to form

Metaphase

-chromosomes move to metaphase plate

-all spindle fibers are attached to kinetochore

Anaphase

duplicated chromosomes split

telophase

(reverse prophase)

-nuclear membrane reforms

-nucleoli reappear

-spindle apparatus desintegrates

-chromosome disperses into chromatin

-cytokinesis

Meiosis

gamete formation

phases of meiosis

Prophase I

Metaphase I

Anaphase I

Telophase I

INTERKINESIS

Prophase II

Metaphase II

Anaphase II

Telophase II

what are the 5 subphases of Prophase I?

Leptotene

Zygotene

Pachytene

Diplotene

Diakinesis

Leptotene

appearance of chromosome as thin, long, thread

zygotene

lateral association of homologous chromosomes

pachytene

consists of the thickening and shortening of bivalents

recombination takes place here

Diplotene

double thread at which homologues begin to separate as the synaptonemal complex begins to break down

Diakinesis

characterized by shortening of homologous chromosomes and terminalization of chiasmata.

tetrad/bivalent

paired homologues

synaptonemal complex

lattice that holds homologues together