The Study of Heredity

Gregor Mendel

Known today as the Father of Genetics, Gregor Mendel was a monk who founded the basis for research and study in the field of heredity today. He began by using pea plants, due to their quick reproduction and growth. He took note of how they crossed and developed three laws, the Rule of Unit Factors, the Rule of Dominance, and the Rule of Segregation.

Alleles and Genotypes

Alleles can be classified in one of two ways; dominant or recessive. Dominant alleles are expressed in offspring in which both alleles are present. The genotype of an individual with both alleles is considered heterozygous, whereas the genotype of one with two dominant or two recessive alleles is considered homozygous. A genotype describes the actual list of alleles for a trait, and a phenotype describes the way which those traits are physically expressed.

Punnett Square

In the above example, a yellow pea pod is crossed with a green pea pod. the offspring of the two would have a 50% chance of being yellow and a 50% chance of being green since the yellow allele is dominate and the yellow pod was heterozygous.

Incomplete Dominance and Codiminance

In some scenarios, heterozygous individuals express both alleles are expressed. In the case of incomplete dominance, a mixture of the two are shown. For example, if you crossed a white cow and a red cow, a pink cow would be produced.

With codominance, a combination of the two alleles are shown, not mixed. For example, in the red cow/ white cow scenario, a spotted red and white cow would be produced.

Multiple Alleles

Multiple alleles are a pattern of inheritance in which traits are controlled by more then 2 alleles. One example of this is blood types, which use the alleles of A, B, and i.

Sex Linked Traits

Sex linked traits are traits which are found on a X or Y chromosome. Examples of these would be hemophilia, colorblindness, and baldness.