Genetics Chapter 3

Mendel is considered the “father” of modern genetics.

Traits are physical characteristics. Factors that control traits are called genes.

The different forms of a gene are called alleles. Each allele is represented by a letter in the genotype. Bb BB bb

An organism’s genotype is its genetic makeup. Genotype is shown with two letters. Rr HH tt Bb GG yy Ss

Alleles can be dominant or recessive. Dominant alleles are always written with a capital letter. Recessive alleles are always written with a lowercase letter. Rr HH tt Bb GG yy Ss

An organism’s phenotype is its physical appearance. Once you know which allele is dominant and which is recessive, you can figure out which trait will “show.” CC cc

If both alleles are the same, the organism is homozygous, or purebred, for that trait. RR HH tt bb GG yy ss

If the two alleles are different, the organism is heterozygous, or hybrid, for that trait. Rr Hh Tt Bb Gg Yy Ss