1. SC.912.L.16.1 Valentina Orrego Period: 3

2. 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.

3. 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.

4. Mendel’s Experiment cont.

5. 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”.

6. 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.

7. Dihybrid Crosses

8. 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.

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

10. Codominance  Another exception to Mendel’s principle is codominance.  Codominance is when the phenotype of both alleles are expressed.

11. 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.

12. 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.

13. 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.