Genetic Variation
Genetic variation refers to the variation in the genome sequences between individual organisms of a species. Individual differences or population differences can both be referred to as genetic variations. It is primarily caused by mutation, but other factors such as genetic drift and sexual reproduction also play a major role.
Quantitative Genetics
Quantitative genetics is the part of genetics that deals with the continuous trait, where the expression of various genes influences the phenotypes. Thus genes are expressed together to produce a trait with continuous variability. This is unlike the classical traits or qualitative traits, where each trait is controlled by the expression of a single or very few genes to produce a discontinuous variation.
The trait of blood pressure in humans has a frequency distribution
that is similar to a normal distribution. The following graph shows
the ranges of blood pressures for a selected population of people.
The red line depicts the frequency distribution of the systolic pressures
for the entire population. Several individuals with high blood
pressure were identified, and the blood pressures of their relatives
were determined. This frequency distribution is depicted with a blue
line. (Note: The blue line does not include the people who were
identified with high blood pressure; it includes only their relatives.)
What do these data suggest with regard to a genetic basis for high
blood pressure? What statistical approach could you use to determine
the heritability for this trait?
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