Patterns of Inheritance: Variation

Inheritance Offspring inherit a mixture of traits from their parents. Some of these traits will be similar to those of one or both of the parents. Some of these traits will be unique to the offspring. All members of a species are slightly different from one another – this is called Genetic Variation.

What is Variation? Variation refers to the differences within a population. The importance of variation is that because all individuals in a population are different, some will be better prepared to survive a change in the environment and re-build the population.

What is Variation? Environmental changes can wipe out the entire population if it has little or no variation.

Types of Variation There are two types of variation: Continuous a range of features can be seen, eg. height or IQ in humans. Discrete or Discontinuous two or several distinct features can be seen, eg. tongue rolling in humans.

Continuous Variation variation that can have many variants within a range. e.g height, hand span, IQ, weight. controlled by several genes

Continuous Variation No. with Trait Trait (eg height) Continuous variation follows a “bell-shaped curve” No. with Trait Trait (eg height) Most people somewhere in the middle Not so many people either really short or really tall.

Discrete Variation variation that is usually limited to two variants. e.g. tongue roll or non-roll, attached earlobe or unattached earlobe. controlled by a single gene

Discrete Variation Discrete variation follows a pattern that is well suited to a bar graph Some people have one variation some have the other.

Discrete Variation Rollers Non-rollers No. of Students Tongue Rolling

Check out Genetic Variation in this class In 4 groups take a class list and survey the class on one characteristic Tongue rolling Height Hand span Ear Lobes Take your results and graph them Compare your graph with others in the class

Causes of Variation There are two main causes of variation: The Environment (environmental variation) -where you live and how you live (can change) Your Genes (genetic variation) -the genetic information that you were given by your parents (unchangable)

Sources Of Variation For sexually reproducing organisms, there are four mechanisms for generating genetic variation: mutation independent assortment of chromosomes crossing over between homologous chromosomes random fertilization

Mutations These are permanent changes in the genetic material of an organism. This can range in size from a single DNA base to a large segment of a chromosome, or even a change in chromosome number. Mutations occur randomly in a population.

Mutations Only a small portion of mutations are likely to be beneficial to the organism. Mutations that occur in body cells are called somatic mutations and can not be passed on to offspring. Mutations that occur in reproductive cells can be passed on.