Section 5-1

1. Section 5-1 What is Genetics?

2. I. What have you inherited? • Heredity is the passing of traits from parents to offspring • Genes control traits • Genes are segments of DNA

3. A. How are traits inherited? • Genes are found on chromosomes in the nucleus of a cell • When pairs of genes separate into sex cells during meiosis, pairs of genes also separate from one another • Each sex cell winds up with one form of a gene for each trait

4. Examples of traits that can be inherited: • Eye color • Hair color • Hair line (straight or widow’s peak) • One sex cell may receive the trait for straight hair line and another sex cell may receive the trait for a widow’s peak • The different forms a gene may have for a trait are its alleles • The study of how traits are inherited is the science of genetics

5. II. The Father of Genetics • The scientific study of traits pass from one generation to the next was done by Gregor Mendel • Mendel’s background in science and math helped him with his studies of genetics • Mendel studied the inheritance of traits in pea plants • Mendel is known as the “Father of Genetics”

6. III. In Mendel’s garden • Why did use pea plants in his experiment? • They are true-breeding – can self-pollinate and produce identical offspring • They can also be cross-bred – one plant pollinates another to produce a genetic combination in offspring • An organism that always produces the same in its offspring is called a purebred • Example: A tall plant that always produces a tall plant

7. A. Dominant and Recessive Factors • Mendel’s first experiment: cross pollinated a purebred of tall plants with a purebred of short plants • The tall trait is considered a dominant factor because it dominated or covered up the short factor • The form of the trait that seemed to disappear is called the recessive.

8. Mendel’s second experiment • Self-pollinated the tall offspring and planted the seeds • The results of this experiment were in a 3:1 ratio. For every 3 tall plants there was 1 short plant. The recessive form reappeared • Genotype:

9. B. Predictions Using Probability • Probability is a branch of mathematics that helps you predict the chance that something will happen • What made Mendel’s predictions accurate? • He produced a large number of plants • By increasing the numbers, Mendel increased his chance of seeing a predicted 3-to-1 ratio

10. IV. Using a Punnett Square • A handy tool used to predict results in Mendelian genetics is a Punnett square • A dominant trait is written with a capital letter and a recessive trait is written with a lower case letter. The letters show the genetic makeup of an organism called the genotype • Phenotype refers to the physical appearance of the trait

11. A. Alleles determine traits • Most cells in your body have two alleles for every trait • An organism with two alleles for a trait that are exactly the same is called homozygous (TT, tt) • An organism that has two different alleles for a trait is called heterozygous (Tt) • The genotype determines an organisms physical traits called the phenotype

12. B. Determining genotypes and phenotypes • In a Punnett square, the letters representing the two alleles from one parent are written along the top of the square and the alleles from the other parent are written along the side of the square • The letters that you filled in each square represent the possible genoytypes for the offspring the parents could produce

13. C. Mendel’s success • Mendel succeeded in describing how inherited traits are transmitted from parent to offspring • 3 summary statements: • Traits are controlled by alleles on chromosomes • An allele’s effect is dominant or recessive • When a pair of chromosomes separates during meiosis, the different alleles for a trait move into separate sex cells