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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