Genetics: Understanding Heredity (How traits are passed from parent to offspring)

Dominant and Recessive Alleles Alleles are the different versions of a gene. Ex/ Gene = height in pea plants One version (allele) codes for a tall stem One version (allele) codes for a short stem Dominant allele – version of the trait that always shows up if it is present Recessive allele – version of the trait that only shows up if the dominant allele is not present

How do alleles control traits? Organisms inherit one allele from each parent (two copies in total) Symbols are used to represent alleles Capital letters represent dominant alleles Lower case letters represent recessive alleles Ex/ Tall stem = T (dominant) Short stem = t (recessive)

Homozygous: When an organisms inherits two of the SAME alleles for a trait Homozygous dominant = TT Homozygous recessive = tt Heterozygous: When an organism inherits two different alleles for a trait (Ex/ Tt)

If T = tall and t = short: TT = tall Tt = tall (dominant covers recessive) tt = short The allele combination is called an organisms genotype (Ex/ Tt) The physical expression of the trait is called the phenotype (Ex/ Tall)

Practice: Determine if the following allele combinations are homozygous or heterozygous: HH Uu Xx PP dd Rr What would be the phenotype for the following genotypes: B = brown fur b = tan fur BB = Bb = bb =

Homework Create a “cheat sheet” of key genetics vocabulary Homozygous Fold a piece of manila paper into 8 boxes In each box, write the genetics term and a picture/illustration/example that will help you remember what the term means. DO NOT JUST WRITE THE DEFINITION! The words to include: Example: Dominant Recessive Homozygous Heterozygous Phenotype Genotype Allele Homozygous Definition: HH hh