Lectures 5-6

Gregor Mendel

Gregor Mendel

worked with garden peas to test family resemblance and genes

true breeding plants

when reproduce all offspring will look like parents (purple x purple = purple)

non-true breeding plants

odd offspring (purple x purple = purple AND white)

the basic cross

bred ture offspring of certain trait with one of different variation of same trait = hybrids

P generation

parent generation (true breeding) (purple and white)

cross fertilize

cross 2 tpes/ variations of a trait

F1 generation

offspring of 1st cross (purple)

self cross

2nd cross, F1s self fertilize

F2 generation

self crossed offspring, color variation (3 purple, 1 white)

dominant trait

captial letter, overriding effect of different variation (will appear visibly)

recessive trait

lowercase letter, masked variation (present at gene level but not visibly seen) (only expressed when genotype is homologous)

F3 generation

1/3 purple breed true, 2/3 purple didn’t

1 element model

parents transmit information (genes) abouut traits to their offspring

2 element model

each individual receives 2 copies (1 from each parent) of each factor (allele) to encode each trait

3 element model

not all factors (alleles) are same, different combinations lead to different traits

4 element model

two alleles dont blend, assemble randomly

5 element model

the presence of an allele doesn’t guarantee it’ll be expressed (can be latent)

homozygote

2 alleles are identical (true breeding)

heterozygote

2 alleles are different (non-true breeding)

genotype

alleles found in individual, AA =/ Aa

phenotype

physical appearance of individual, AA (homozygous) =/ Aa (heterozygous)

phenotype ratio

3:1

genotype ratio

1:2:1 (1 homo dominant, 2 hetero, 1 homo recessive)

Mendels 1st law of heredity

Principle of Segregation - 2 alleles segregate during gamete formation to be rejoined at random during fertilization (1 from each, latent traits)

the punnett square

50% mom’s heterozygous gametes dominant/recessive, same for dad

Dihybrid cross

2 traits

dihybrid ratio

9:3:3:1

Mendels 2nd law of herdity

Principle of Independent Assortment - in a dihybrid cross the alleles of each gene assort independently

gene linkage

2 genes linked on same chromosome will be passed down together but will only get offspring with same phenotypes as parents

genes far apart on same chromosome

get segregated during meiosis recombination

polygenic inheritence

phenotype trait attributable to 2 of more genes, quantitative/ continuously varying trait

polygenic inheritence example

height with lots of variation and multiple traits controlling it and disease (difficult)

pleiotropy

simgle gene affects 2 or more characteristics

incomplete dominance

both alleles found in the genotypei

incomplete codominance

a mixture of the alleles in the genotype visible in the phenotype

environmental effects on gene expression

sickle cell anemia and decrease sensitivity of malaria

epistasis

phenotype traits attributable to 2 or more genes that interact (1 modifies/ hides another)

epistasis example

hair color and baldness, fur coat and amount of melanin

codominance example

mice offspring with patches of black and grey fur

number of human chromosomes

46, 23 from mom and 23 from dad

how chromosomes are passed on

cell division that produces gametes

karyotype

complete map set of chromosomes

chromatids

before they replicate, sisters with identical info

centromere

what holds 2 sisters together

chromosomes

paired sister chromatids

homologous pair

same chromosome from mom and dad, same type and genes

why might homologous pair differ

may have different alleles

mitosis phases

interphase, prophase, prometaphase, metaphase, anaphase, telophase

interphase

DNA diffuses and replicates

prophase

chromatin condenses into visible chromosomes with identical paired sister chromatids

prometaphase

nuclear envelope breaks, microtubules go to poles/ opposite ends

metaphase

chromosomes line up at equator, condensed and highly coiled (can get best visual)

anaphase

sisters pulled apart, new daughter moves to poles

telophase

cell cleaves in half, daughters enter interphase again separately

Meiosis phases

early prophase , mid prophase , prometaphase, metaphase 1, anaphase 1, telophase 1, prophase 2, metaphase 2, anaphase 2, telophase 2

early prophase

chromosomes condense

mid prophase

homologous pairs join

prometaphase

pairs cross over

metaphase 1

pairs align at equator

anaphase 1

homologous chromosomes move to poles (sisters dont separate)

telophase 1

cell divides to form sister cells

prophase 2

chromosomes recondense but DNA doesn’t replicate

metaphase 2

centromeres line at equator

anaphase 2

pulled apart and chromosomes move to poles

telophase 2

chromosomes gather into nuclei and cell divides

meiosis products

4 cells with nucleuses with chromosomes

meiosis process

start with 2 DNA, divides 1st into normal amount of DNA then divides again into half as much as normal cell (gametes join)

ploidy

number of copies of chromosomes

haploid

a cell with one copy of each chromosome 1N

diploid

cell with 2 copies of each chromosome 2N

polyploid

more than 2 copies of each chromosome xN

mitosis ploidy

2N to 4N to 2N

meiosis ploidy

2N to 4N to 2N to 1N

crossing over

homologous chromosome pairs (meiosis) have enzymes released that can break and rejoin chromatids

recombination

DNA from non-sister chromatids can be exchange ie. dad chromosome with mom DNA

likeliness of recombination

variable, some might have many or few

recombination leads to

genetic variation (meiosis), reshufflings

gene linkage

in F1 generation, genes are unlinked, 4 gamete combinations are produced (RY,Ry,rY,ry)

all the following are true regarding meiosis except

gametes produced are diploids - are actually haploid

Wilhelm Johannsen

created term gene as unit for inherited traits

Thomas Hunt Morgan

genes rest on chromosomes

George Beadle and Edward Tatum

1 gene codes for 1 enzyme

Oswald Avery, Maclyn McCarty and Colin Macleod

genes are made of DNA

Rosalind Franklin

structure of DNA (helical), Photo 51

the double helix

DNA comprised of 2 intertwined strands of nucleotids

nucleotids fixed along

2 helical backbones made of repeating sugar and phosphate units

nucleotids held together by

hydrogen bonds between nucleotids, paired specifically together

4 nucleotides

Adenine (A), Thymine (T), Cytosine (C), Guanine (G)

adenine forms

2 hydrogen bonds with thymine

cyotsine forms

3 hydrogen bonds with guanine

how DNA replicates

single parental strand with 2 chains can replicate to 2 daughter strands with exact same information that’s rarely lost

semi econservative replication

produces molecule with both old and new DNA, each molecule contains 1 complete old strand and 1 new one

DNA replication

helix unzips, breaking bonds between paired nucleotids, number of enzzymes bring new nucleotides to the parental chain and form new parent chains

DNA polymerase

match existing nucleotides on parental chain with complementary bases, to form bond between new pairs

the central dogma

portions of DNA get converted into RNA that provides intstructions to cell for production of proteins, who do work of the cell

RNA

single strand of DNA

DNA to RNA

transcription

transcription

works similar to DNA replication

RNA to protein

translation

translation

RNA sequence used to synthesize a polypeptide (protein)