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genetics test 2 - Coggle Diagram
genetics test 2
mendelian genetics
before mendel
- preformationism: organisms develop from miniature versions of themselves
mendel crossed peas (because they can self-fertilize) and found:
gene: discrete unit of inhertiance
allele: version of a gene
complete dominance: one allele version will conceal the presence of the other version
green and yellow peas:
- SGR gene degrades chlorophyll which is essential for plant efficiency
- mutation in SGR gene (six bp insertion) disrupts chlorophyll degradation causing green pea plant
wrinkled vs round pea:
- starch branching enzyme makes pea round
- mutation (800bp insertion) causes SBE to not function and the pea accumulates sucrose
- after insertion, protein is shorter because of a premature stop codon somewhere
on a gel:
- smaller pieces of DNA run faster so are farther down
- DNA is negative so current across gel moves it through mesh
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continuous variation: traits whose phenotypes occur on a continuum instead of having a limited number of possible phenotypes. can be polygenic traits but not always
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law of segregation: in a diploid organism, each nuclear genome carries two alleles (mom + dad) but only one will be encoded in each gamete (punnet squares)
homologous chromosomes: same size and carry same assortment of genes but may have diff alleles
genetic recombination: homologous chromosomes exchange genetic material creating genetic diversity
law of independent assortment: genes on separate linkage groups are independently assorted. the allele a gamete receives for one genes doesn't affect the allele a gamete receives for a different, independent gene
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mendel was lucky because:
- picked traits determined by one loci
- picked traits that act additively and are unlinked
- phenotypic ratios were very close to theoretical expectatios
genes and alleles
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genes don't have to have two alleles only, they can have more and all w different degrees of dominance
human blood has ABO locus (i) that encodes an enzyme responsible for adding sugar to blood cells, more than one alleles
the DNA of A and B are relatively similar but O has a deletion causing a frameshift mutation and truncates the protein --> doesn't have sugar on red blood cell
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defining dominance for quantitative trait:
d = F1 value - u (mean parental values)
a = Pm - u
d/a = 1, maternal --> completely dominant
d/a = -1, maternal --> completely recessive
d/a = 0, no dominance
d/a > 1, d/a < -1, over dominance
epistasis: when an allele at one locus masks or silences the presentation of a phenotype from an allele at another locus
recessive epistasis: when a recessive allele masks the effect of dominant and recessive alleles at another locus
example: color of labs --> E codes for a gene that makes eumelanin. if you have one E allele then eumelanin will be there. you also need an enzyme to deposit eumelanin. functioning eumelanin and enzyme =. black lab. functioning eumelanin but not deposit = brown lab. no eumelanin = yellow lab
dominant epistasis: a dominant allele masks the effect of dominant and recessive alleles at another locus
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reciprocal recessive: a recessive allele masks at either locus and masks the effect of the other locus (ex: pink vs white flower)
redundant genes: recessive alleles at both loci combined mask the effects of an individual locus (ex: triangle vs oval bud)
this can happen because of gene duplication. where DNA is duplicated through unequal crossing over during meiosis or retrotransposition. one copy retains function and another can get mutated
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linkage
map distance: indicator of # of crossovers between two loci. longer map distance, higher recombination frequency because more physical distance between two genes
to find recombination frequency, assign parental and recombinant phenotypes to each genotype
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crossover interference:
- physical constraint
- chromatin structure
- regulatory mechanisms
genotype frequencies: proortion of total individuals in the population with a particular combination of alleles
allele frequencies: the relative frequency of an allele at a particular focus in a population, expressed as a fraction or percentage
hardy-weinberg principle: after one generation of random mating, genotype frequencies will be p^2, 2pq, q^2 (freq A=p, freq a = q)
inheritance
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chromosomal theory of inheritance: genes are located at specific positions on chromosomes and chromosomes are the basis of genetic inheritance
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meiosis: results in genetically distinct progeny cells (gametes) from two back-to-back cell divisions that result in four progeny cells (haploid cells) per division. recombination and crossing over also occurs
autosomes = human chromosomes, sex chromosomes = X and Y that have a PAR region that has sequence homology allowing them to pair up
x-linked genes: genes located on x chromosomes --> mostly more commonly expressed in males because they have to have one X. can escape inactivation
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