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Genetics-lecture 8- populations

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winniesmith1's version from 2017-05-14 23:24

Section 1

Question Answer
Why do we care about population variations 1. Genetic variations underlie phenotypic differences among different individuals. 2.Genetic variations determine our predisposition to complex diseases and responses to drugs and environmental factors. 3.Genetic variations reveal clues of ancestral human migration history.
How do genetic variations originate-Mutations are the primary source. -Gene or point mutations or repeat size changes. -Chromosomal recombination and change in chromosome numbers.
What is the gene pool Total number of genes in a population
What is a locusPosition of a gene on the chromosome
What is an alleleDifferent/alternative forms of the same gene
What is gene/allele frequencyProportion of a particular type of allele at a genetic locus.
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Section 2

Question Answer
What is the hardy-weinberg equilibrium (HWE)In a large population with random mating, allele and genotype frequencies do not change from one generation to the next after the 1st generation.
When does the HWE oocuronly under certain assumptions; -Random mating -Infinite population size -No mutation or selection -No migration. BUT assumptions frequently violated in nature. Has nothing to do with pattern of expression/inheritance.
Statistical evaluation of HWE 1. Work out the allele frequencies. 2. From allele frequencies work out expected genotype frequencies using (p+q)2 = p2 +2pq+q2. 3. Multiply expected genotype frequencies with number tested (no of samples) to get EXPCETED NUMBERS. 4. Now you have Observed and Expected numbers use Chi-Square to test significance.
How do you know if the value is in significant departure from HWEIf the value is higher than the chi squared value
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Section 3

Question Answer
What are single gene traits and disorders different phenotypes resulting from alternative genotypes of a single gene
What do crosses and pedigrees showThat the number of genotypes and phenotypes is small and that the relationship between them is simple.
Are the majority of traits/diseases qualitative or quantitativequalitative
Many traits/phenotypes/diseases arecomplex traits or multifactorial traits (because multiple genetic and environmental factors are involved).
What is complex inheritancea single genotype can have many possible phenotypes and a single phenotype can be caused by many possible genotypes.
Give examples of quantitative and continuous traitscommon diseases, diabetes, hypertension, obesity, heart disease, cancer.
What are polygenic traits result from the interactions of more than one gene. More influenced by environmental factors.
Examples of common phenotypes/diseases which are polygenic heart disease, BP, AD, diabetes).
Why can the most complex traits not be studied with usual pedigree methodsBecause; Environmental effects may cause identical genotypes to have different phenotypes AND Effects of segregation of alleles of one gene may be masked by effects of other genes
How do you analyse a polygenic traistThey are; Measurement, normal distribution (connecting the points of a frequency distribution creates a bell-shaped curve), regression to the mean.
What are the 3 types of polygenic traits-Continuous traits or quantitative traits (Height/Weight). -Meristic traits (counting) (eg Ridge Count). -Threshold traits (Risk or liability threshold, few classes).
As the nm. of loci affecting the trait increases, what happens to the nm. of phenotypic categories they increase. As number of phenotypic categories = (no. of gene pairs x 2)+1
What % of a normal distribution lie within 1 SD, 2 SDs and 3 SDs of the mean 1= 68%. 2= 95%. 3=99.7%
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Section 4

Question Answer
What do continuous traits givea range of phenotypes
How can biological traits be analysedfrequency distribution, mean,mode, median, SD. Correlation/regression coefficient.
What is the correlation coefficienta measure of strength of association between 2 variables (from -1 to +1)
What do correlations not implycause and effect. They may exist for many reasons.
What is the regression coefficientused for precise relationships, to predict if one variable changes, how much the other one will change.
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Section 5

Question Answer
What are dermatoglyphics (finger prints)Pattern of ridges on the friction skin of the fingers, palms, toes and sole.
What is special about dermatoglyphicsThey are unique to the individual and unchanged over a lifetime.
When are dermatoglyphics formedin utero by about 4-5 months
What are the common patterns on dermatoglyphicsArches, loops and whorls
Disease associations; dermatoglyphics; trisomy 21Usually all are ulnar loops and Simian Creases in 50%.
Disease associations; dermatoglyphics; turner syndromePredominance of whorls
Disease associations; dermatoglyphics; 47, XXYExcess of arches
Disease associations; dermatoglyphics; Trisomy 13Excess of arches and Simian creases in 60%
Disease associations; dermatoglyphics; Trisomy 186 - 10 arches and Simian creases in 30%
Disease associations; dermatoglyphics; Cri du chat (5p-)Excess of arches and Simian creases in 90%
Disease associations; dermatoglyphics; hypertensionAll whorls have higher predisposition!
What are dermal ridge counts determines byare almost all genetically determined
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Section 6

Question Answer
What is heritability measure of contribution of genes and environment.is the ratio of genetic variance (VG) to total phenotypic variance (VP); H = VG/VP
What is a phenotype heritability dependent on upon Genetics and Environment
What is heritability variances caused by phenotypic, genptypic and environmental factors.
What variation among a phenotype known as Vp- phenotypic variance.
What is a phenotype the result ofa genotype interacting with the environment
What is phenotypic variance due to both variation in the genes and variation in the environment (Vp=Vg+Ve)
What is the heritability of obesity in children and adults Children 0.77-0.88, Adults: 0.64-0.80.
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