Genetics

Genetics is… the scientific study of heredity (traits that are passed from parent to offspring).

The Work of Gregor Mendel Mendel’s Peas

Genes Mendel determined that… – Traits are inherited as a result of factors passed from parents to offspring – We now know that these “factors” are genes

What is a Gene? With your table group discuss what you think a gene is. Write or draw your agreed description on your whiteboard. What is a Gene

Genes (contd.) Allele – the different or alternate form of a gene. – For example: Flower color in pea plants has 2 alleles: purple and white

Different forms of a gene are written as capitol and lower case letters. Dominant alleles will be expressed if they are present. Violet (purple) flower color is dominant over white color. The allele for violet is written as P Recessive alleles are written with lower case letters. The allele for white is written as p

Genotype vs. Phenotype Phenotype is the physical characteristic of a trait of an organism. – Example: Tall or short Genotype is the genetic makeup of a trait. – Example : Tt, TT, or tt.

Homozygous vs. Heterozygous Homozygous – two identical alleles for a particular trait. – Example : TT or tt Heterozygous – two different alleles for the same trait. – Example Tt

Why do you have two copies of every gene? You have two of each chromosome, one from each parent. Each chromosome has hundreds to thousands of genes.

Punnett Squares A Punnett square is a tool to show how the alleles can combine in order to predict the possible genotypes and phenotypes of offspring.

Before we go further lets review how to set up a Punnett Square… We begin by constructing a grid of two perpendicular lines.

Next, put the genotype of one parent across the top and the other along the left side. For this example lets consider a genotype of BB crossed with bb. B B bbbb Notice only one letter goes above each box It does not matter which parent’s genotype goes on either side.

Next, fill in the boxes by copying the column and row head-letters down and across into the empty spaces. B B b B B B B b b b b b

Punnett Square Practice Draw a punnett square on your paper or whiteboard.

Lets say: W- dominant white w- recessive violet W w W Complete a cross with two parents that are heterozygous (Ww). Note: Make sure I can tell your capital letters from lowercase letters. What percentage of the offspring will have violet flowers? ANSWER: 25% (homozygous recessive) Usually write the capital letter first w W W w w

Work this problem on your whiteboard or paper. In pea plants, tall pea plants (T) are dominant over short pea plants (t). Construct a Punnett Square for a heterozygous tall pea plant and a short pea plant. Tt tt Tt tt T t tttt What are the percentage of phenotypes? 50% tall 50% short

Punnett Square Independent Practice. Use the Zork Genetics trait chart to work out the following crosses: 1.Cross two heterozygous one leg Zorks. What are the percentages of each genotype? What are the percentages of each phenotype? 2. Cross one homozygous green lips with a heterozygous purple lips Zork. Give the genotypic and phenotypic percentages

Now do it backwards 3. If you have the following #s of offspring determine the possible genotypes of the parents: a.48 Zork babies with one eye and 12 Zork babies with three eyes b.60 Zork babies with green hair and none with yellow hair. c.54 Zork babies with thick eyebrows and 51 Zork babies with thin eyebrows Support your answers with punnett squares

Now predict 4.Two Zorks had 78 offspring. 15 had no wings and 63 had wings. What are the chances that their next offspring will not have wings? Support your answer with punnett squares

Create and show the genotypes for your Zork Your Zork must have 10 traits with at least 3 homozyogous dominant, 3 heterozygous and 3 homozygous recessive traits. Make a list of the genotypes and phenotypes Draw and color your Zork.