EXAM 3 Gen Bio

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two assumptions if early studies of inheritance

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1

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)

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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

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law of segregation

-two alleles will separate into different gametes

  • egg or sperm only get one of two alleles

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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

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Mendel's sample experiment steps

  1. prevent self fertilization

  2. pollinate

  3. collect seeds (peas)

  4. plant peas

  5. examine offspring

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character

observable, physical feature (flower color)

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trait

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

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heritable trait

passed from parent to offspring

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hybridization

crossing 2 true breeding plants

  • round seeds X wrinkled seeds

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

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recessive traits in Mendel's experiment

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

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dominant trait in Mendel's experiment

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

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particulate theory

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

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Mendel's model

STUDY IN NOTES

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alleles

different forms of a gene

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homozygous

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

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heterozygous

Individuals have two different alleles (Ss)

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phenotype

physical appearance of an organism

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genotype

the genetic makeup of an organism

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test cross

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

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monohybrid cross

plants are heterozygous for only one trait

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dihybrid cross

when two traits are both hybrid

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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

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results of Mendel's 2nd experiment

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

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probability

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

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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

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mutation

rare, stable, inherited changes in the genetic material

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wild type

allele present in most of the population other alleles are mutant

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mutant

alternative phenotype

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polymorphic

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

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mendelian rule breakers

co-dominance, blood group system, incomplete dominance

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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

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Blood (ABO) group system

3 alleles at 1 locus

<p>3 alleles at 1 locus</p>
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incomplete dominance

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

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

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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)

<p>Greek: stopping, standing over</p><ul><li><p>one locus (gene) alters the phenotype of a second gene Ex: color in labs</p></li><li><p>allele B (black) dominant to b (brown)</p></li><li><p>allele E (pigment deposition) is dominant to e (no pigment deposit, yellow)</p></li></ul>
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trihybrid cross

LOOK AT NOTES PRACTICE

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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

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sex is determined by...

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

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autosomes

both sexes have two copies of all other chromosomes

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XX

female

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XY

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

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SRY gene

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

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DAX 1 gene

on the x chromosome which produces a anti-testis factor

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if SRY gene is present...

inhibits DAX 1 maleness inhibitor and the embryo develops testes

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If SRY gene is NOT present

DAX 1 functions to inhibit maleness and the embryo develops ovaries

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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

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linkage

genes connected based on physical location

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parental types

when linked, the phenotypes we expect

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recombinants

the products of crossing over between the genes

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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

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crossing over

recombination of linked genes during meiosis

  • average 1-3 cross over per pair

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frequencies are greater...

for loci that are farther apart

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recombinant frequency

how often we see recombinants

of recombinants/ total offspring

  • can be used to make genetic maps

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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

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map unit (centimorgan)

distance between genes, recombinant frequency of 0.01= CM

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x inactivation

females= 2 X chromosomes male= 1 X chromosomes

  • one female X chromosome is randomly is inactivated at early embryogenesis

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nondisjunction

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

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nondisjunction during meiosis

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

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deletion

loss of DNA

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duplication

repeat of DNA

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inversion

reversal of segment

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translocation

exchange between 2 chromosomes

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bacteria exchanges genes by...

conjunction

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sex pilus

a projection that initiates contact between bacterial cells

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conjunction tubes

cytoplasmic bridge that forms between cells

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plasmids

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

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Frederick Griffith

studied strep phenomena

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2 strains

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

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

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heated S strain

not virulent

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heat killed s strain + R strain

virulent

  • bacteria that grew was smooth R strain was transformed

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DNA

genetic material that has the ability to perform transformation

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4 nitrogenous bases

  1. adenine

  2. guanine

  3. cytosine

  4. thymine

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purines

adenine and guanine

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pyrimidines

cytosine and thymine

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DNA structure (Watson and crick, pauling, Franklin)

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

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A-T

two hydrogen bonds

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C-G

3 hydrogen bonds

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deoxyribose structure

sugar of DNA

  • 5- carbon

  • 1st carbon nitrogenous base attaches

  • 3, 4, 5 DNA backbone

<p>sugar of DNA</p><ul><li><p>5- carbon</p></li><li><p>1st carbon nitrogenous base attaches</p></li><li><p>3, 4, 5 DNA backbone</p></li></ul>
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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

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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

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semi- conservative method

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

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dispersive

DNA chopped into pieces and mismatched into each cell

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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.

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semiconservative DNA replication steps

  1. unwind parental DNA

  • separate two strands

  1. add new nucleotides by complimentary base pairing

  • linked by phosphodiester bond

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helicase

unwinds/ separates 2 strands of DNA

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dna polymerase

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

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Primer

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

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leading strand

synthesized DNA that is continuous

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lagging strand

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

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Okazaki fragments

fragments on the lagging strand

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single stranded binding protein

hold strand apart

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topoisomerase

relieves supercoiling tension

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DNA polymerase I

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

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DNA ligase

seals nick left by Pol I (makes phosphodiester bond)

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overhang

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

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telomeres

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

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telomerase

extends the ends of chromosomes, reverse transcriptase- works backwards

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

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

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errors in replication

  • DNA polymerase error rate 1/10 s bases

  • 60,000 mutations/ replication

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proofreading activity

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

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