SC.912.L.16.1Valentina OrregoPeriod: 3

Gregor Mendel Austrian monk, also known as the “father

of modern genetics”, that discovered the basic principles of heredity.

Mendel performed a series of experiments in his monastery's garden using pea plants.

This experiment lead to the base of modern genetics, and the study of heredity.

Mendel’s Experiment

Mendel cross-pollinated pea plants, which resulted in them having two parents.

He then proceeded to study 7 different traits of pea plants, each having a contrasting characteristic.

The offspring of these crosses are called First Filial generation, or F1.

Mendel’s Experiment cont.

Principle of Dominance Based on the experiments Mendel

concluded that some alleles are dominant while others are recessive.

A dominant allele determines an organisms appearance. It is the one that is shown.

A recessive allele has no noticeable effect. It is “hidden”.

Dihybrid crosses Upon his conclusions, Mendel used

probability to explain the results of his genetic crosses.

A dihybrid cross is a cross between two individuals that differ in two traits.

A punnett square is usually used to express the dihybrid crosses.

Dihybrid Crosses

Incomplete Dominance There are some exceptions to Mendel’s

principles, meaning an allele can neither be dominant nor recessive.

Incomplete dominance is one of these exceptions.

It is when an allele is not completely dominant over another.

Incomplete dominance

An example is shown in the image below. A red and white flower are crossed, and the offspring produced are pink.

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Codominance Another exception to Mendel’s principle is

codominance. Codominance is when the phenotype of

both alleles are expressed.

Multiple Alleles Genes that have more than two alleles

are known as multiple alleles. The best example for these genes is

illustrated by the ABO blood Group system.

A is dominant to O, B is dominant to O and A and B are co dominant.

This results in 4 groups: A, B, O & AB.

Polygenic Inheritance Polygenic Inheritance is a kind of

inheritance in which is a trait controlled by many genes.

Some examples are human skin color, height, and weight.

About 4 different genes control skin color.

Sex-Linked inheritance Genes located on the sex chromosomes (X

and Y chromosomes) show a pattern of inheritance called sex- linkage.

Genes located on the X chromosome are found in both sexes, while genes located on the Y chromosome are only found in males.

For example, the genes corresponding to color vision are all located on the X chromosome.

This is the reason color blindness is more common in males than in females.