(a) (b) FIGURE 1.9 Examples of chiromosome variation. (a) A person with Down syndrome. She has 47 chromosomes rather than the common number of 46, because she has an extra copy of chromosome 21. (b) A wheat plant. Cultivated wheat is derived from the contributions of three wild species with two sets of chromosomes each, producing an organism with six sets of chromosomes. (a): © Stockbyte/Alamy RF; (b): © Brand X Pictures/PunchStock RF CONCEPT CHECK: Do these examples constitute variation in chromosome structure or variation in chromosome number?
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.
(a) A person with Down syndrome. She has 47 chromosomes rather than the common number of 46, because she has an extra copy of chromosome 21.
(b) A wheat plant. Cultivated wheat is derived from the contributions of three
wild species with two sets of chromosomes each, producing an organism
with six sets of chromosomes.
Do these examples constitute variation in chromosome
structure or variation in chromosome number?
Step by step
Solved in 4 steps
