Investigation 9: Genetic Variation
Goal: In Genetic variation students will learn the basis genetic
mechanism that determines the traits expressed by individuals
in a population
 The individuals in every population vary from one
another in their traits.
 Heredity is the passing of information from one
generation to the next.
 Chromosomes are structures that contain hereditary
information and transfer it to the next generation; they
occur in nearly identical pairs in the nucleus of every cell.
 Genes are the basic unit of heredity carried by
chromosomes. Genes code for features of organisms.
 Alleles are variation of genes that determines traits in
organisms; the two alleles on paired chromosomes
constitute a gene.
 Alleles can be dominant or recessive. Dominant alleles
exhibit the effect if they are present on one chromosome;
recessive alleles exhibit their effect only when they are on
both chromosomes.
 An organism’s particular combination of paired alleles is
it genotype; the traits produced by those alleles results in
the organism phenotype.
 A gene composed of two identical alleles (e.g. both
dominant and recessive) is homozygous; a gene
composed of two different alleles (i.e. one dominant and
on recessive) is heterozygous.
If both parents are carriers of the recessive
allele for a disorder, all of their children will
face the following odds of inheriting it:
25% chance of having the recessive disorder
50% chance of being a healthy carrier
25% chance of being healthy and not have
the recessive allele at all
If one parent is a carrier and the other has a
recessive disorder, their children will have the
following odds of inheriting it:
50% chance of being a healthy carrier
50% chance having the recessive disorder
If only one parent has a single copy of a
dominant allele for a dominant disorder,
their children will have a 50% chance of
inheriting the disorder and 50% chance
of being entirely normal.