Genetics: Inheriting Traits

I. Inheriting Traits A. An organism characteristics is the collection of many traits inherited from its parent(s) 1. Heredity- passing of traits to offspring B. Traits are determined by genes on chromosomes – 1. Alleles are different forms of a trait

II. What is Genetics? A. Genetics- the study of how traits are inherited through the interactions of alleles B. Gregor Mendel “The Father of Genetics” 1 st to trace one trait through several generations. – 1. Mendel used pea plants and probability to explain the process

III. Mendel’s Garden A. Mendel crossed two plants with different expressions of a trait. – 1. New plants from the crosses looked like one of the two parents he called hybrids Ex. Tall Pea plant mate with a Short pea plant = Tall pea plant offspring **Note: Why are all the offspring Tall and not Short?

III. Mendel’s Garden cont. B. Mendel noticed when cross-breeding plants some traits seemed to disappear while others were always present – 1. Traits that are always present and seem to cover up the other trait are dominant – 2. Traits that seem to disappear or are “covered up” are recessive

IV. Using Probability A. Using probability helps you determine or predict what a cross’s offspring will look like. B. Punnett squares- a tool to help predict what the crosses results will look like Parent 1 Parent 2 X Allele 1Allele 2 Allele 1 Allele 2

IV. Using Probability cont. C. The Alleles are represented by Upper and Lowercase letters – 1. Uppercase letters =dominant traits – 2. Lowercase letters =recessive traits D. The two letters for each trait is called the genotype. E. The way an organism looks is known as the phenotype.

V. Alleles Determine Traits A. Every cell in your body has at least two alleles for every trait located on chromosomes. – 1. If an organism has two of the same alleles the trait is known as homozygous A. Ex. TT or tt – 2. If an organism has two alleles that are different it is known as heterozygous A. Ex. Tt

VI. Punnett Squares A. Place two alleles for one parent on the top and the two alleles for the second parent along the side B. The square is then filled in with one allele donated by each parent Parent 1 Parent 2 X Allele 1Allele 2 Allele 1 Allele 2

VI. Punnett Square cont. C. Cross a Tall plant homozygous dominant with a Short homozygous recessive plant What is the probability the plants will be Tall? Short? Tall Plant Short Plant X TT tTt t

Lets Practice Heterozygous Tall pea plant with Heterozygous Tall pea plant Heterozygous Tall pea plant with a homozygous recessive short pea plant Homozygous Tall pea plant with a heterozygous Tall pea plant