An Intro to Unit 4: Heredity Mendel and Genetics An Intro to Unit 4: Heredity

Genetics Key Vocabulary Before we begin, there are a few words you need to know. Directions: Use your Reader and the word bank on the top of your notes paper to identify the correct definition of each vocabulary word. You have 15 minutes and may work with a partner quietly or by yourself (headphones allowed).

Who is Gregor Mendel? An Austrian monk in the 1800’s Father of modern genetics Bred pea plants to learn about inheritance (passing down of traits from one generation to another).

What did Gregor Mendel do? Mendel crossed two purebred pea plants, one with yellow peas and the other with green peas. He called this generation the P or parent generation. When he crossed the P generation to produce offspring, he called these offspring the G1 or 1st Generation. He found that all of the G1 plants had yellow peas. Therefore he called yellow the dominant trait. When he bred the G1 plants with one another to creat the G2 generation though, he found that approximetly 75% of the peas were yellow and 25% of the peas were green. He called green the recessive trait, because while it was hidden in one generation (or skipped a generation) it was still present in some of the offspring.

What does this mean & why should I care? Some traits are more likely to appear than others. These are called dominant traits and we write these traits in capital letters. Some traits are masked or covered up by dominant traits and are less likely to appear. These are called recessive traits and we write these traits in lowercase letters.

Yellow vs. Green In the case of pea color, yellow is dominant and green is recessive. Therefore we write yellow with a capital Y and green with a lowercase y. Because these two letters look similar in upper and lower case, I underline the uppercase for emphasis.

Yellow vs. Green The genotype of the purebred yellow pea from the P generation was YY or homozygous dominant. It has two uppercase Y’s, one from each of its parents. We know that they are both uppercase because the plant is a purebred. The phenotype of this pea is “yellow.” YY

Yellow vs. Green The genotype of the purebred green pea from the P generation was yy or homozygous recessive. It has two lowercase y’s, one from each of its parents. We know that they are both lowercase because the plant is a purebred. The phenotype of this pea is “green.” YY

G1 Offspring When Gregor Mendel crossed the YY yellow plant with the yy green plant, it created 100% Yy offspring. We call these offspring heterozygous because they have one uppercase letter and one lowercase letter. The phenotype of this plant was yellow. Yy

Punnett Squares: G1 We use a model called a Punnett Square to help us predict the genotype and phenotype of offspring in the 1st generation. Y y Yy

Punnett Squares: G1 We use a model called a Punnett Square to help us predict the genotype and phenotype of offspring in the 1st generation. Y y Yy Because all of the offspring have at least one uppercase Y, the color that we see for them is yellow. Therefore 100% of the offspring in G1 have yellow peas.

Punnett Squares: G2 If we use the same model to then cross offspring from G1 and create G2, we notice a different outcome. Y y YY Yy yy

Punnett Squares: G2 If we use the same model to then cross offspring from G1 and create G2, we notice a different outcome. Y y YY Yy yy Now, 25% of the offspring will be green because 25% of them have two recessive genes, just like their grandparent, the original green pea.

Still confused? Check this out! https://www.youtube.com/watch?v=Mehz7tCxjSE