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.
Different species of crickets have distinct songs, and
they use these songs for mate recognition. Researchers
crossed two species of Hawaiian crickets (Laupala paranigra and L. kohalensis) whose songs are distinguished
by pulse rate (the number of pulses per second; Shaw et
al., Molecular Ecology 16, 2007, 2879–2892.) Then, they
mapped QTL in the F2 population derived from this
cross. Six autosomal QTL were detected. The mean trait
values (pulses per second) at the three genotypic classes
in the F2 for each QTL are shown in the table below,
where P indicates the L. paranigra allele and K indicates
the L. kohalensis allele.
a. Calculate the additive (A) and dominance (D) effects
and the D/A ratio for each of the six QTL.
b. Which of these QTL shows the greatest amount of
dominance?c. Which of these has the largest additive effect?
d. The mean pulse rate for L. kohalensis is 3.72, and it is
0.71 for L. paranigra. Do all six QTL act in the expected
direction with the L. kohalensis allele conferring a higher
pulse rate than the L. paranigra allele?
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