Genetics The study of heredity; how traits are passed from parent to offspring. x = or

Heredity - passing of physical characteristics from parents to offspring

Fertilization- A new organism begins to form when egg and sperm join. Happens in plants and animals. Purebred-Organism is the offspring of many generations that have the same trait. Hybrid- Organism who has 2 different alleles for a trait.

The study of heredity started with the work of Gregor Mendel and his pea plant garden Mendel was an Austrian Monk that lived in the mid 1800’s

Genetics: The Science of Heredity - Mendel’s Work Crossing Pea Plants Gregor Mendel crossed pea plants that had different traits. The illustrations show how he did this.

Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results.

Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants. Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. X = x = X =

Genetics: The Science of Heredity - Mendel’s Work Mendel’s Experiments In all of Mendel’s crosses, only one form of the trait appeared in the F 1 generation. However, in the F 2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants.

Genetics: The Science of Heredity - Mendel’s Work Dominant and Recessive Alleles Mendel studied several traits in pea plants. Traits are different forms of a characteristic, such as stem height or seed color

Mendel’s work led him to the understanding that traits such as plant height are carried in pairs of information not by single sets of information. -Carrying the information are chromosomes. -Chromosomes are made up of sections called genes. -Genes are made up of DNA

DNA D.N.A. - Deoxyribonucleic Acid Molecule made of: 1. Deoxy Sugar 2. Combination of four nitrogen bases Either:a. Guanine b. Cytocine c. Thymine d. Adenine The sum total of combinations that these four bases are capable of creating are greater than all the stars visible in the night time sky

DNA Nitrogen bases pair up –Cytosine & Guanine –Thymine & Adenine Pairing creates a ladder shape Angle of bonds creates a twist Ladder and Twist produces the famous “Double Helix”

DNA DNA resides in all cells –Inside the nucleus Each strand forms a chromosome Cell Nucleus DNA

DNA is found in all living cells –It controls all functions inside a cell –It stores all the genetic information for an entire living organism –Single cell like an amoeba –Multi cell like a human

Genetics Small sections of DNA are responsible for a “trait”. These small sections are called “Genes”. –Gene - A segment of DNA that codes for a specific trait –Trait - A characteristic an organism can pass on to it’s offspring through DNA Gene

Genetics There are three basic kinds of genes: –Dominant - A gene that is always expressed and hides others –Recessive - A gene that is only expressed when a dominant gene isn’t present

Genetics Dominant and Recessive Genes A dominant gene will always mask a recessive gene. A “widows peak” is dominant, not having a widows peak is recessive. If one parent contributes a gene for a widows peak, and the other parent doesn’t, the off- spring will have a widows peak. Widows Peak

Genetics Punnet Square - A tool we use for predicting the traits of an offspring –Letters are used as symbols to designate genes –Capital letters are used for dominant genes –Lower case letters are used for recessive genes –Genes always exist in pairs –Alleles are different forms of a gene, like having a widows peak or no widows peak.

Genetics A Widows Peak, dominant, would be symbolized with a capital “W”, while no widows peak, recessive, would be symbolized with a lower case “w”. Father - No Widows Peak - w Mother - Has a Widows Peak - W

Genetics: The Science of Heredity Percentages One way you can express a probability is as a percentage. A percentage (%) is a number compared to 100. For example, 50% means 50 out of 100. Suppose that 3 out of 5 tossed coins landed with heads up. Here’s how you can calculate what percent of the coins landed with heads up. 1. Write the comparison as a fraction. 3 out of 5 = 3/5 2. Multiply the fraction by 100% to express it as a percentage. 3/5 x 100%/1 = 60% - Probability and Heredity

Genetics: The Science of Heredity Percentages Practice Problem Suppose 3 out of 12 coins landed with tails up. How can you express this as a percent? 25% - Probability and Heredity