Genetic differences between identical Twins All individuals, even monozygotic twins, differ in their repertoire of antibodies and t-cell receptors(because of epigenetic rearrangements and somatic cell mutations); somatic mutations in general the numbers of mitochondrial dna molecules(epigenetic partitioning) the pattern of x inactivation, if female
Genetic Differences between Identical Twins • All individuals, even monozygotic twins, differ in: –their repertoire of antibodies and T-cell receptors (because of epigenetic rearrangements and somatic cell mutations); –somatic mutations in general –the numbers of mitochondrial DNA molecules (epigenetic partitioning); –the pattern of X inactivation, if female
Genetic analysis of quantitative traits Correlation Heritability
Genetic analysis of quantitative traits • Correlation: • Heritability:
Correlation is a statistical measure of the degree of association of variable phenomena(a measure of the degree of resemblance or relationship between 2 parameters). Table 9.3 Degrees of relationship Relationshi Proportion of genes shared First degree 1/2 Parents Siblings Children Second degree 1/4 Uncles and aunts Nephews and nieces Grandparents Grandchildren Half-siblings Third degree 1/8 First cousins Great-grandparents Great-grandchildren
Correlation is a statistical measure of the degree of association of variable phenomena (a measure of the degree of resemblance or relationship between 2 parameters)
Coefficient of correlation (r) Positive correlation:r>l No correlation: r=O Negative correlation: r<1
Coefficient of correlation (r) • Positive correlation: r>1 • No correlation: r=0 • Negative correlation: r<1
Heritability(n2)遗传率: The proportion of the total variation of a character attributable to genetic as opposed to environment factors MZ DZ h2 100--CDZ If c Dz then h2 is high(approaches 1) If Cmz=Cpz then h is low(approaches 0) Ic=concordance
Heritability (h 2 )遗传率: The proportion of the total variation of a character attributable to genetic as opposed to environment factors. CMZ -- CDZ • h 2 = ----------------------- 100 -- CDZ • If cMZ >> cDZ then h 2 is high (approaches 1) • If cMZ = cDZ then h 2 is low (approaches 0) [c = concordance]