Flashcards in test 2 Deck (37):
1
big exception to mendel's ideas
chromosome theory and linkage
2
sutton/boveri chromosome theory
genes are located on chromosomes
-genes (alleles) and chromosomes both occur in pairs
-allele pairs and chromosome pairs both separate from each other and enter separate gametes
-separation of both allele pairs and chromosome pairs are independent
3
proof of chromosome theory
morgan created research group called Drosophila group
group showed that certain gene was on the X chromosome and therefore the chromosome theory must be true
4
morgan's observations
strange results from cross between white-eyed female and red-eyed male (all red-eyed females and all white-eyed males)
could only explain strange results if he assumed the white-eyed gene was on the X chromosome
5
bridge's final proof of chromosome theory
experiment with nondisjunction where he produced XXY female
in various sex chromosomes that resulted from these females, the X chromosome and the white eye gene seemed to be transmitted together
proof was first article in first volume of journal Genetics
6
X linkage in humans
genes on X chromosome=X linked
ex: hemophilia A and red green color blindness
7
sex linked genes
gene on X or Y chromosome
8
how many PARs on X and Y chromosomes
2 PARs
at tip of each telomere
9
linkage
more than 1 gene is located on each chromosome so 2 genes found on the same homologous pair of a chromosome will not obey mendel's law of independent assortment
alleles will move together (linked)
for a 2 point cross there are 2 possibilities
10
parental and recombinant gametes
gametes F1 individual makes are either:
-same combo of alleles as P generation
-opposite combo of alleles as P generation
11
independent assortment vs. linkage
if genes are on different chromosome pairs they will assort independently (# of P gametes will be ~equal to # of recombinant gametes)
if 2 genes are on same chromosome pair they will not assort independently but will be linked (# of P gametes will be significantly greater than # of recombinant gametes)
12
recombinant gametes and crossing over
for linked genes recombinant gametes are produced by crossing over between 2 genes
even if crossover occurs the products of a single meiotic event will be 2 parental and 2 recombinant alleles
13
predicting outcome of dihybrid cross involving linked genes
punnet square using probabilities
list gamete genotypes and probability of each gamete (probability calculated if you know distance between genes)
probabilities of each gamete pair multiplied together giving frequency of each genotype
14
gene mapping
for linked genes the distance between is proportional to the frequency of crossing over
further apart 2 genes are the more likely a crossover will occur between them
ex: 1% recombinant gametes=1 map unit or cM
max distance=50 cM
15
3 point test cross
used bc 2 point test crosses often overlook double crossovers
individual crossed with homozygous recessive
analysis reveals gene order, distance between genes, and the degree of interference
16
steps of 3 point cross
1. determine gene order
2. determine distance between genes
3. calculate coefficient of coincidence
17
what is the coefficient of coincidence
decimal that expresses what proportion of expected double crossovers actually happened
18
mapping in organisms with an ordered tetrad
ascomycetes (all products of single meiosis in sac)
some have cells maintained in order in which they are produced by meiosis I and II (possible to map distance between gene and its centromere)
4 of 1 kind on top and 4 of other kind on bottom
19
somatic cell hybridization
technique used in 1960s to map some human genes to chromosomes or even regions of a chromosome
fusion of human tissue culture cell to mouse cell
human cells preferentially lost so you can get cell with all mouse chromosomes but 1 human chromosome so if cell still produces specific human product then gene for that product must be on that chromosome
20
FISH
fluorescent in situ hybridization
technique involves hybridizing a probe DNA molecule (tagged with fluorescent marker) to a spread of chromosomes
21
SNPs and GWASs
single nucleotide polymorphisms and genome-wide associated studies
use common variants of a single DNA base pair as markers to hunt for genes related to a trait or disease
22
LOD score
log of odds favoring linkage
used in population genetics
pedigree analysis can be used to infer linkage of 2 genes
estimate probability that pedigree was produced by 2 genes linked at a given distance vs. produced by 2 non linked genes
23
discovery of nucleic acids
miescher
isolated new substance from nuclei of cells ("nuclein") which he realized was new class of organic material
knew it wasn't protein bc it had no S but had P
nuclein was probably mixture of DNA and RNA
"nucleic acids" today
24
DNA as genetic material of almost everything
avery, macleod, and mccarty
showed DNA was genetic material of bacterium that causes type of pneumonia in mice
based on griffith experiment with bacteria with/without capsule (S and R) ("transforming principle")
25
RNA as genetic material of some viruses
some viruses have no DNA but do have RNA
some RNA viruses replicate their RNA using RNA replicase or enzyme reverse transcriptase to make DNA intermediate which is then copied to RNA
viruses called "retroviruses"
26
DNA structure
polynucleotide (polymer of nucleotides)
27
DNA polynucleotide
polynucleotide made by joining many nucleotides together
3' pentose sugar bonded to 5' phosphate of next nucleotide
DNA has sugar-phosphate backbone with bases protruding off 1 side
28
nucleotide
each DNA (or RNA) nucleotide is composed of 3 subunits (phosphate, pentose, base)
29
nucleoside
pentose and base (no phosphate)
30
purines
have a double ring structure and are larger than pyrimidines
adenine and guanine
31
pyridines
single ring structure and are smaller than purines
cytosine and thymine (uracil replaces thymine in RNA)
32
the double helix
watson and crick proposed 3-D model for structure of DNA (double helix)
work based on x-ray crystallography work of Franklin and Wilkins and work of chargaff (A=T and G=C) and general understanding of structure of DNA polynucleotide
33
strands of DNA
2 antiparallel nucleotide strands running in opposite polarity
34
alpha helix
the 2 strands are coiled in an alpha helix (right handed helix)
35
specific base pairing
A always paris with T and G always pairs with C
base pairing is by hydrogen bonding involving N, O, and H
3 bonds that hold G to C
2 bonds that hold A to T
36
dimensions of the double helix
3.4 A thick and stacked internally
with of molecule is 20 A and makes 1 complete turn ever 34 A
10 base pairs per turn of the helix
37