Introduction to Genetics Mendel and His Pea Plants

Think About It Has anyone ever told you that you look like your Mom? Or your Dad? Or an uncle, aunt, or a grandparent? In what ways do you look like the people in your family?

Look around What traits do you share with other people in this class? Are there traits you have that no one else in this class has?

Why do you look like you do? You probably know you get your physical characteristics from your parents. But, why do some kids look like one parent more than the other, or they don’t look like either parent? To understand how this happens, let’s talk about the scientist who figured it all out. But first, there are…

Some Words You Need to Know Traits – characteristics such as eye color, hair color, or shape of eyebrows Heredity – the passing of traits to offspring Genetics – the study of heredity

Gregor Mendel (1822-1884) “Father of Genetics” Austrian monk Studied the traits of pea plants

Why pea plants? Pea plants are easy to grow Pea plants have a lot of traits that can be studied A lot of their traits have only two varieties: Tall or short Round seeds or wrinkled seeds Yellow seeds or green seeds Purple flowers or white flowers Green pods or yellow pods

Some Pea Plant Traits

More about plants In plants, male and female reproductive parts are found in every flower. (There are no boy plants or girl plants.) The male reproductive organs produce pollen (plant sperm). The female reproductive organs produce eggs. Self-pollination – when a plant fertilizes itself Cross-pollination – when a plant is fertilized by another plant

Mendel’s Experiment Mendel controlled how plants were fertilized by: removing the male parts from some flowers so they could not produce pollen. This means they could not self-pollinate. using a brush to move pollen from one flower to another In other words, Mendel decided which plants were going to be the parents of the offspring.

Mendel’s Experiment Part 1 First, Mendel crossed (bred) a purebred short plant with a purebred tall plant. He called these plants the P1 Generation. Purebred tall plant X Purebred short plant

Mendel’s Experiment Part 1 Mendel called them purebreds because the short one came from a family of all short plants, and the tall one came from a family of all tall plants. You will learn a different meaning for purebred later.

Mendel’s Experiment Part 1 What size of offspring do you think the purebred short and purebred tall plants produced? All of the offspring were… TALL!! They never produced any short offspring.

Mendel’s Experiment Part 2 Next, Mendel self-pollinated the offspring from the first generation. He called them the F1 Generation. Tall Plant X Tall Plant He called these offspring produced by these plants the F2 Generation.

Mendel’s Experiment Part 2 What size of offspring of the F2 Generation do you think this produced? About three out of four of the offspring were tall, but one of every 4 was short.

To sum it up

What happened? Turn to the person sitting next to you and explain why you think Mendel got these results from his experiment. (Hand out PPT note-frames.)

What did Mendel figure out? Each parent contributes a substance that controls the traits of their offspring. For example, each parent contributes a substance for the height, the seed color, the seed shape, etc.

What we now know Those substances that control traits are called genes and they are part of chromosomes. Chromosomes, you should remember, are found in the nucleus of cells.

What we now know We have two genes for every trait. One comes from the male parent and one comes from the female parent. The different forms of a gene are called alleles.

Some examples of genes & alleles Mendel’s pea plants had two genes for their height. The alleles for that gene are short and tall. The pea plants had two genes for flower color. The alleles for that gene are purple and white. The pea plants had two genes for their seed shape. The alleles for that gene are round and wrinkled.

What else did Mendel figure out? One allele can mask, or hide, the other allele. If one parent gives the offspring an allele that says a plant should have green seeds and the other parent contributes an allele that says the offspring should have yellow seeds, one of them will mask the other one.

More words to know Dominant allele – an allele that can mask another allele and always “shows up” if present Recessive allele – an allele that can be masked by a dominant allele and only “shows up” if both alleles for a trait are recessive

Symbols used for alleles Dominant alleles are always represented by a capital letter. The first letter of the dominant trait is usually used. For example, if tall is dominant in pea plants, then T represents that allele. Recessive alleles are always represented by the lower case letter of the dominant allele. Since short is recessive in pea plants, t represents that allele.

Are you getting it so far? How would you write the symbols for a pea plant that has one allele for purple flowers and one allele for white flowers if purple is dominant? Pp What color flowers would that plant have? purple

Are you getting it so far? How would you write the symbols for a pea plant that has two alleles for purple flowers? PP What color flowers would that plant have? purple

Are you getting it so far? How would you write the symbols for a pea plant that has two alleles for white flowers? pp What color flowers would that plant have? white

Phenotypes & Genotypes Phenotype – a physical trait of an organism ex. purple flower Genotype – the genetic makeup of an organism; it determines the phenotype ex. PP Next year switch the order --

Phenotypes & Genotypes Examples: Genotype Phenotype PP PURPLE flowers Pp PURPLE flowers pp WHITE flowers

Try these Fill in the missing information. Phenotype Genotype tall _t short _ _

Try these Fill in the missing information. Phenotype Genotype tall Tt short _ _

Try these Fill in the missing information. Phenotype Genotype tall Tt short _ _

Try these Fill in the missing information. Phenotype Genotype tall Tt short tt

A few more words Homozygous or purebred – 2 of the same alleles for a trait examples: PP, pp, TT, tt Heterozygous or hybrid – 2 different alleles for a trait examples: Pp, Tt

YouTube - Mr. Lee - Genetics rap