Mendel wondered if genes that determine different traits affect one another.

He did an experiment to find out. Mendel found that the gene for

seed shape did not affect how the gene for seed color sorted.

He summarized his conclusions as the principle of independent assortment.

The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.

Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms.

Summary of Mendel’s Principles – The inheritance of

biological characteristics is determine by units known as genes. In organisms that reproduce sexually , genes are passed from parents to their offspring

Summary of Mendel’s Principles – In cases in which two

or more forms of the gene for a single trait exist, some forms of the gene may be dominant and others are recessive

Summary of Mendel’s Principles – In most sexually

reproducing organisms, each adult has two copies of each gene, one from each parent. These genes are segregated from each other when gametes are formed

Summary of Mendel’s Principles – The alleles for

different genes usually segregate independently from one another.

There are many exceptions to Mendel’s Principles– Not all genes show simple

patterns of dominant and recessive alleles.

– Some alleles are neither dominant nor recessive,

– many traits are controlled by multiple alleles or multiple genes.

Incomplete Dominance – Ex. Cross between a red

(RR) flower and a white (rr) flower produce a pink (Rr) flower

– Which allele is Dominant? Neither

– The heterozygous phenotype is somewhere in between the two homozygous phenotypes

Codominance – both alleles appear as part

of the phenotype of the heterozygous offspring.

– Ex. cattle with an allele for red hair is codominant with the allele for white hair. Cows coat is spotted with a mixture of both red and white hairs

Multiple Alleles– many genes can have more

than two available alleles. – This does not mean that an

individual can have more than two alleles

– It means that more than two possible alleles exist in a population

– Ex. coat color in Rabbits

Multiple Alleles– a rabbits coat’s

color is determined by a single gene that has at least 4 alleles

– Produce four separate coat colors

Applying Mendel’s Principles– Mendel’s basic principles

can be used to study human inheritance

Ex. Rare disorder Alkaptonuria was discovered and fit into the Mendelian pattern

Wide variety of genes were discovered, one of which was the gene for skin coloration

Applying Mendel’s Principles– The gene’s dominant

allele (A) produces skin coloration

– Individuals who are homozygous for the recessive form of the allele (a) have ALBINISM

Lack pigment melanin that gives human skin its color

Applying Mendel’s Principles– ALBINISM

If two people with normal skin color have a child with albinism, what are the odds that their second child will be an albino?

By constructing a Punnett Square, you will see that there is a 1 in 4 probability