Biol 207 - Genetics 2
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the frequency of the dominant allele within a population
frequency of recessive allele within a population
- p2 + 2pq + q2 = 1
- both the genotype frequencies and allele frequencies in a population are unchanged following matings within a population.
- Random mating: individuals mate together with equal frequencies
- No natural selection: genotypes have equal fitness
- No migration: no leaving or entering of the population
- No mutation: allele frequencies do not change due to mutation
- Large population: need a large population to reduce random sampling effects (genetic drift)
when genotypes preferentially mate together. type of non-random mating
carry two alleles at each of two loci. heterozygous for alleles of two genes.
- typical phenotypic dihybrid cross ratio results. ratio's can be obtained by using the product rule for each of the monohybrid cross results.
- assumes loci assort independently
- assumes complete dominance of alleles
- assumes phenotypes can be interpreted easily with no interactions between the genes
Law of Independant assortment
two loci assort independently of each other during gamete formation
alleles of loci located close together on the same chromosome tend to be inherited together.
The interaction of genes that are not alleles, in particular the suppression of the effect of one such gene by another. The phenotype differs from what would be expected if the loci were expressed independently and indicates the genes interact in the same biological pathways
- when a singly homozygous recessive genotype (aaB_ or AAB_) has the same phenotype as the double homozygous recessive (aabb).
- 9:3:4 ratio
when a dominant allele at one locus masks the second locus' phenotype
ex: A allele is epistatic to both B and bb combinations so whenever there is "A" that will produce only 1 allele no matter what the second allele produces.
Duplicate Gene Action
When two loci have redundant functions in the same biological pathway so that they both produce identical phenotypes. only the double recessive phenotype shows a different phenotype.
Complementary Gene Action
when the genes work together (complementary) to produce a final product and without each other a loss of function occurs
process resulting in gametes with combinations of alleles that were not present in previous generations gametes
Independant assortment of alleles whose loci are on different chromosomes
recombination occurring through crossovers between loci on the same chromosome.
products of meiosis that resulted in recombination of gametes
- products of meiosis which have original genotypic combinations
- aka non-recombinant
no physical connections between loci. loci are on different chromosomes, will segregate independently.
50% chance of recombinant or parental gametes with unlinked loci.
- number of recombinant gametes divided by the total number of gametes.
- Maximum 50% (unlinked loci)
- Min 0% (complete linkage)
- aka absolute linkage
- loci are so close together on the same chromosome that parental combinations of alleles always segregate together. no crossovers ever occur.
aka partial linkage
when two loci are located on the same chromosome but the loci are far enough them occur sometimes but not always during meiosis
alignment/connection of homologous chromosomes during prophase 1 of meiosis 1
double strand breakage of a pair of non-sister chromatids which then connect to the opposite chromatid and exchange sections of DNA. occurs during prophase 1 of meiosis via synapsis.
- two dominant alleles are together on a chromosome and the two recessive alleles are together on another chromosome
recessive and dominant alleles are together on one chromosome
map units (mu) or centiMorgans (cM)
units of gentic distance. proportional to the RF.
shorter distances are more accurate (RF<30%) and maxes out at 50%
by combining the results of multiple genetic distances the loci of a chromosome can be obtained therefore giving a rough idea of positions of loci relative to other loci.
when two crossovers occur between the loci which creates gametes with the same genotypes as a non-recombination event (50% RF)
Three -point cross
pure breeding lines with different genotypes are crossed producing a triple heterozygous individual which is testcrossed. Allows the order and distance between three linked genes to be determined.
techniques involving the study of DNA and macromolecules that have been isolated from an organism
combination of techniques to isolate and analyze DNA or RNA transcribed from a particular gene
dissolve membranes and denature proteins
protects DNA by sequestering Mg2+ ions, which otherwise would act as a co-factor for nucleases
enzymes which digest DNA
contains DNA and smaller metabolites
small clump of DNA that forms after centrifugation. Can be used in other reactions after addition of water.
Polymerase Chain Reaction: method of DNA replication and amplication
- 1) add DNA polymerase + nucleotides + DNA template + DNA primers + pH buffer + ions (Mg2+)
- 2) Thermacycling: series of precise temperatures. first 95oC
- 3) Annealing: cooling (45-65oC) that allows forming of double stranded helices and annealing of primers to templates
- 4) Extension: 72oC temp allows for DNA polymerase to be most active and synthesize the new DNA strand starting from the primer.
- repeat 30 times.
Taq DNA pol
from Thermus acquaticus it is a thermostable DNA polymerase which allows it to survive the increased temperatures during PCR.
- enzymes that recognize a specific DNA sequence and cuts the DNA helix at this location
- aka restriction enzymes
ends of DNA that have an overhanging single stranded section. caused by certain restriction enzymes
ends of DNA that have been cut without leaving any overhanging single strands
when DNA strands are covalently joined, end to end. accomplished by enzyme called DNA ligase
complementary overhanging sticky ends and blunt ends are compatible but non complementary sticky ends are not and won't be ligased together
small circular double stranded molecules that replicate independently.
describes the process of inserting a DNA plasmid into a bacteria
cells that have been prepared so that they can uptake DNA. Done through exposue to CaCl2 or electical fields (electroporation)
gene present on a plasmid that is transformed into a bacteria in order to differentiate between bacteria that have the uptaken plasmid and those that don't
A bacteriophage, plasmid, or other agent that transfers genetic material from one cell to another
used to detect and analyse DNA.
done by DNA being put at one end of a gel (made of agarose) and then DNA is pushed by an electrical current (towards positive electrode).
shorter sections of DNA will travel further so molecules are separated by length of DNA forming bands.
a fluorescent dye that is used to make DNA bands visible in gel electrophoresis
- 1)DNA is digested with restriction enzymes and put through gel electrophoresis
- 2) nylon or similar material is put under the gel and through "blotting" the DNA is transferred to the nylon membrane and covalently attached through UV light
- 3) hybridization solution containing a probe DNA (labled with flourescent or radioactive molecules) that is complementary to the target molecule is used to bath the membrane
- 4) washing of the membrane to remove extra probe
- 5) exposure to X-ray shows the probe location and therefore the fragment size
Temperature and washing solutions change the "stringency" (specificity) of the probe. Higher temp = more exact
same procedure as the Southern blot except with RNA and without restriction enzymes in order to observe the full size of an RNA transcript
same procedure as the southern blot except with proteins and use of an acrylamide gel. the probe is an antibody that binds to an antigenic site on the target protein. These probes are observed by adding other antibodies with flourescent or colour marker systems
failure of chromosomes to segregate properly during any Anaphase
cells that have the proper number of chromosomes
cells that have one too many or one too few chromosomes. both cells will likely die.
aneuploid cells that have two many copies or too many copies of hundreds of genes. (over or underproduction)
First division nondisjunction
a nondisjunction during Anaphase 1 of meiosis. results in unbalanced gametes, which will still fertilize but the embryo won't likely survive
Second division nondisjunction
a nondisjunction during Anaphase 2 of meiosis. results in unbalanced gametes which will still fertilize but the embryo won't likely survive.
nonhomologous end joinging system: repair system to fix double strand breaks through proteins binding to ends of DNA and reattaching covalent bonds.
when the NHEJ system proteins join the ends of improper strand brekas. Can occur when there are multiple double strand breaks.
changes in chromosome structure
- 1) incorrect repair of double strand DNA breaks during interphase
- 2) incorrect crossovers during meiosis
both breaks on one chromosome and a section is removed
Both breaks on one chromosome and a section is flipped in the chromosme
inversion that does NOT include the centromere
inversion that DOES include the centromere
one break on each homologous chromosomes or sister chromatids where a section is stolen from one chromosome and put onto another
breaks occurring on unrelated chromosome where chromosomes exchange sections.
when both chromosomes contribute and swap sections.
- when all the genes of a translocation end up on one chromosome and the other becomes tiny and is lost.
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