EXAM 3 Gen Bio

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135 Terms

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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
3 alleles at 1 locus
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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
2 alleles result in a combined phenotype 
Ex: crossing a dark pink and white flower resulting in offspring that is lighter pink
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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)
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)
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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
sugar of DNA 
- 5- carbon 
- 1st carbon nitrogenous base attaches 
- 3, 4, 5 DNA backbone
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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
2) 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