EXAM 3 Gen Bio

two assumptions if early studies of inheritance

1. Each parent contributed equally to offspring in reciprocal crosses (supported)

2. hereditary determinants blend in offspring (non supportive)

Gregor Mendel

studies refuted the early assumptions
studied inheritance in pea plants (only two possibilities)
- started with true breeding plants and allowed for them to self pollinate for similar offspring

law of segregation

-two alleles will separate into different gametes
- egg or sperm only get one of two alleles

law of independent assortment

each member of a pair of homologous chromosomes separates independently of the members of other pairs so the results are random
- doesn't always apply to genes on the same chromosome; but they do segregate independently

Mendel's sample experiment steps

1. prevent self fertilization

2. pollinate

3. collect seeds (peas)

4. plant peas

5. examine offspring

character

observable, physical feature (flower color)

trait

a form of a character (purple flowers or white flowers)

heritable trait

passed from parent to offspring

hybridization

crossing 2 true breeding plants

• round seeds X wrinkled seeds

• results: F1 all round, F2: 3:1 round:wrinkled

recessive traits in Mendel's experiment

the traits that disappear in the F1 generation (wrinkled seeds)

dominant trait in Mendel's experiment

the trait that appears in the F1 generation (round seeds)

particulate theory

the heritable units were desecrate particles
-each parent has two particles for each character, one from each parent

Mendel's model

STUDY IN NOTES

alleles

different forms of a gene

homozygous

true breeding individuals have 2 copies of the same allele (SS or ss)

heterozygous

Individuals have two different alleles (Ss)

phenotype

physical appearance of an organism

genotype

the genetic makeup of an organism

test cross

how to determine the genotype of an organism- cross an unknown with a homozygous recessive

monohybrid cross

plants are heterozygous for only one trait

dihybrid cross

when two traits are both hybrid

SsYy linked or segregated?

If linked: gametes would be SY or sy; F2 would have three times more spherical yellow than wrinkled green

If independent: gametes could be SY, sy, Sy or sY; F2 would have 9 different genotypes; phenotypes would be 9:3:3:1

results of Mendel's 2nd experiment

recombinant phenotypes resulting in a 9:3:3:1 ration

probability

event certain to occur - probability = 1
event NOT to occur - probability = 0

dihybrid cross

probability that F2 seeds will be spherical is 3/4: probability of heterozygote + probability of homozygote 1/2 + 1/4= 3/4
joint probability that a seed will be spherical and yellow 3/4 x 3/4 = 9/16

mutation

rare, stable, inherited changes in the genetic material

wild type

allele present in most of the population other alleles are mutant

mutant

alternative phenotype

polymorphic

locus with wild-type allele present less than 99% of the time

mendelian rule breakers

co-dominance, blood group system, incomplete dominance

co-dominance

two alleles at one locus produce phenotypes that are both present in the heterozygote
EX: Roan cattle
WW- color
W'W'- white
WW'- both

Blood (ABO) group system

3 alleles at 1 locus

incomplete dominance

2 alleles result in a combined phenotype
Ex: crossing a dark pink and white flower resulting in offspring that is lighter pink

polydactyly

birth defect characterized by the presence of more than the normal number of fingers or toes
DOMINANT TRAITS AREN'T ALWAYS THE MOST COMMON

Epistasis

Greek: stopping, standing over

• one locus (gene) alters the phenotype of a second gene Ex: color in labs

• allele B (black) dominant to b (brown)

• allele E (pigment deposition) is dominant to e (no pigment deposit, yellow)

trihybrid cross

LOOK AT NOTES PRACTICE

Drosophila experiment

didn't yield expected ratios according to law of independent assortment

• genes inherited were said to be linked

• all of the loci on a chromosomes form a linkage group

found: genes are linked for eye color with genes that determine sex

sex is determined by...

a single sex chromosome or by a pair
also which chromosome fertilizes the egg

autosomes

both sexes have two copies of all other chromosomes

XX

female

XY

male
produce two kinds of gametes- half carry a Y and half carry a X

SRY gene

on the Y chromosome
-encodes a protein involved in primary sex determination

DAX 1 gene

on the x chromosome which produces a anti-testis factor

if SRY gene is present...

inhibits DAX 1 maleness inhibitor and the embryo develops testes

If SRY gene is NOT present

DAX 1 functions to inhibit maleness and the embryo develops ovaries

sex linked genes

many genes unrelated to sex are on the X chromosome
For recessive genes
---- Females: inherit recessive from both parents
------Males: inherit recessive from mother (hemizygous), inherit Y from father

linkage

genes connected based on physical location

parental types

when linked, the phenotypes we expect

recombinants

the products of crossing over between the genes

absolute linkage

rare genes at different loci on the same chromosomes do sometime separate

• genes may recombine during prophase I of meiosis by crossing over

• chromosomes exchange corresponding segments, The exchange involves two chromatids in the tetrad both chromatids become recombinant

crossing over

recombination of linked genes during meiosis
- average 1-3 cross over per pair

frequencies are greater...

for loci that are farther apart

recombinant frequency

how often we see recombinants

of recombinants/ total offspring

• can be used to make genetic maps

genetic map

shows arrangement of genes along a chromosome

• can be applies to find relative distance on chromosomes

• higher chance of recombination between distant genes than nearby genes

map unit (centimorgan)

distance between genes, recombinant frequency of 0.01= CM

x inactivation

females= 2 X chromosomes
male= 1 X chromosomes
- one female X chromosome is randomly is inactivated at early embryogenesis

nondisjunction

failure of chromosome or chromatids to separate, extra copy in one cell and loss in another

nondisjunction during meiosis

sex chromosomes
kleinfelter syndrom- XXY sterile male
Turner syndrome- XO sterile female
XYY- normal male
XXX- normal female

deletion

loss of DNA

duplication

repeat of DNA

inversion

reversal of segment

translocation

exchange between 2 chromosomes

bacteria exchanges genes by...

conjunction

sex pilus

a projection that initiates contact between bacterial cells

conjunction tubes

cytoplasmic bridge that forms between cells

plasmids

small circular chromosomes besides the main one, can move between the cells during conjunction

Frederick Griffith

studied strep phenomena

2 strains

1. S (smooth)- causes you to get sick (virulent)

2. R (rough)- non virulent (doesn't cause you to get sick)

heated S strain

not virulent

heat killed s strain + R strain

virulent
- bacteria that grew was smooth
R strain was transformed

DNA

genetic material that has the ability to perform transformation

4 nitrogenous bases

1. adenine

2. guanine

3. cytosine

4. thymine

purines

adenine and guanine

pyrimidines

cytosine and thymine

DNA structure (Watson and crick, pauling, Franklin)

bases are on the interior
2 strands run antiparallel
helix and uniform diameter

A-T

two hydrogen bonds

C-G

3 hydrogen bonds

deoxyribose structure

sugar of DNA

• 5- carbon

• 1st carbon nitrogenous base attaches

• 3, 4, 5 DNA backbone

essential characteristics of DNA

1. stores genetic information

2. genetic material is subject to mutations

3. genetic material is precisely replicated in cell division

4. genetic material is expressed as a phenotype

conservative method

• takes old stand and copy it exactly the same

• old strands would go to one cell and new copy went to the other

semi- conservative method

each cell got an old copy and new copy THIS IS TRUE

dispersive

DNA chopped into pieces and mismatched into each cell

gel electrophoresis

Gel electrophoresis is a technique used to separate DNA fragments according to their size. DNA samples are loaded into wells (indentations) at one end of a gel, and an electric current is applied to pull them through the gel. DNA fragments are negatively charged, so they move towards the positive electrode.

semiconservative DNA replication steps

1. unwind parental DNA

• separate two strands

2. add new nucleotides by complimentary base pairing

• linked by phosphodiester bond

helicase

unwinds/ separates 2 strands of DNA

dna polymerase

synthesizes DNA in 5'-3' direction (specifically III)

Primer

RNA sequence to start replication
-cant add DNA from nothing - needs a 3' hydroxl group

leading strand

synthesized DNA that is continuous

lagging strand

strand is made backwards, starting from primer and is in fragments

Okazaki fragments

fragments on the lagging strand

single stranded binding protein

hold strand apart

topoisomerase

relieves supercoiling tension

DNA polymerase I

removes primer, writes DNA on lagging strand, can't make phosphodiester bond between 3 OH group and phosphate

DNA ligase

seals nick left by Pol I (makes phosphodiester bond)

overhang

every time we synthesize DNA the extreme end gets an overhang because primer is removed in turn getting shorter

telomeres

repeated the same sequence (TTAGGG) cap the end of the chromosome to protect it

telomerase

extends the ends of chromosomes, reverse transcriptase- works backwards

DNA-----> RNA ------> protein

-----------> transcription --------------> translation

errors in replication

• DNA polymerase error rate 1/10 s bases

• 60,000 mutations/ replication

proofreading activity

can reread what is added and if wrong it can fix it (3'-5' exonucleotylic activity) , error rate decrease