Genetics & Heredity

Genetics & Heredity Using the vocabulary to discuss and predict the outcome of genetic crosses

Objectives • By the end of this interactive presentation you • Will have reviewed key genetics vocabulary already discussed in class • Will be able to distinguish between genotype and phenotype • Will be able to analyze data from a genetics experiment in order to predict your genotype for various traits.

Why do we call Mendel the “Father of Genetics?” • He was the first person to discover genes. • He understood that DNA was where genes were. • He was the first person to see chromosomes. • His was the first person to study inheritance in depth.

Reviewing Mendel Mendel observed that some traits seemed to “mask” or override other traits. What did Mendel call these traits? • Dominant traits • Recessive traits • Co-dominant traits

Reviewing Mendel • Mendel called the traits that seemed to “overpower” others dominant traits. • We represent the allele for dominant traits with a capital letter. • For example, • Tall is dominant over short, T • Round is dominant over wrinkled, R • Yellow is dominant over green, Y

Reviewing Mendel • The traits that were masked were called recessive traits. • We represent the allele for a recessive trait with a lowercase letter. • For example • Short (recessive to tall), t • Wrinkled (recessive to round), r • Green (recessive to yellow), y

Reviewing Mendel Which individual will express the recessive short trait? • Tt • TT • tt

Punnett Squares • On a piece of loose leaf create and complete a Punnett Square to predict the outcome of the following genetic cross • Round peas are dominant to wrinkled. What are the possible outcomes if a RR plant was crossed with a Rr plant?

Punnett Squares RR x Rr R r R R

Punnett Squares In the previous Punnett Square, what are the odds of having a heterozygous offspring? • 100% • 75% • 50% • 25%

Vocabulary Review • Remember: • Homozygous means 2 of the same allele. • Homophone: words that sound the same. • Heterozygous means 2 different alleles. • Heterogeneous: a mixture that is different throughout. (For example, when your iced tea is sweet at the bottom, but not at the top)

New Vocabulary • Phenotype • The physical characteristic (trait) that is expressed is the phenotype. • Genotype • The alleles or the genes that the organism has. • For example: • Tt is the genotype, tall is the phenotype • RR is the genotype, round is the phenotype • yy is the genotype, green is the phenotype

Let’s Practice • What is the phenotype of… • Yy • SS • pp • YY • ss

Let’s Practice • Determine the genotypes • Green seeds • Pinched pods • White flowers

Let’s Practice We can only predict the genotype of Individuals expressing dominant traits. Why might this statement be true? • Dominant traits are less common. • A dominant phenotype must mean 2 dominant alleles. • A dominant phenotype could mean 2 dominant alleles OR 1 dominant and 1 recessive allele.

For example • Yellow seeds are dominant to green seeds. A pea plant producing yellow seeds can be either YY or Yy. • Without knowing more information about the parents, you cannot be positive. • On the other hand, a pea plant producing green seeds MUST be yy. • In order for the recessive allele to show, you must have 2 recessive alleles.

Let’s Practice • For each phenotype, give the genotype(s) that are possible. • Yellow • Smooth • Purple

Time to Review! The factors that control our traits are called… • Alleles • Traits • Genes • Chromosomes

Time to Review! An organism who is homozygous has • Two different alleles • Two dominant alleles • Two recessive alleles • Two of the same alleles, recessive or dominant.

Time to Review! The different forms of a gene are called • Traits • Genotype • Genes • Alleles

Time to Review! Which of the following is a genotype? • Yellow • Homozygous • Rr

Time to Review! Which of the following is a phenotype? • Yellow • Homozygous • Rr

The End

Genetics & Heredity