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Thursday February 14, 2013 Warm Up: Draw a Punnett Square to represent a cross between a homozygous recessive plant and a heterozygous plant. • Trait is height • Tall is dominant Happy Valentine’s Day Love, Ms. Archie and Ms. Johnson MYP Unit Question- How did you get those traits you have? Area of Interaction- Human Ingenuity Learning Target: Today I will learn why punnett squares are useful because they allow me to see the chance of what genes will be handed down to the offspring. Chapter 5-1 Genetics Heredity is the passing of traits from the parents to the offspring and is controlled by genes Gregor Mendel Father of Genetics Gregor Mendel Born in 1822 in Austria and lived in Europe. Was a monk who studied mathematics and science. Determined the basic laws of Genetics. Mendel’s Garden As a boy, he worked in his father’s orchard and became interested in plants He experimented with peas. Self-Pollinating Peas have both male and female reproductive structures. So, pollen from one flower can fertilize the ovule of the same flower. When a true-breeding plant self pollinates, all of the offspring will have the same trait as the parent. Pea plants can also cross-pollinate. Pollen from one plant fertilizes the ovule of a flower on a different plant. The image below shows crosspollination and self-pollination. Characteristics Characteristics Mendel studied only one pea characteristic at a time. A characteristic is a feature that has different forms in a population. Ex: Human hair color Different forms of a characteristic are called traits. Gregor Mendel Called the form of a trait that appears to dominate or mask another form of the same trait dominant. Gregor Mendel Called the weak form of a trait that is prevented from showing up by a dominant trait recessive. Chapter 5 section 2 So, what is genetics? Genetics is the study of how traits are inherited through the actions of alleles. What are genes? Instructions for an inherited trait. Made of segments of DNA Control the traits of an organism Found on the chromosomes Have different forms called alleles What are alleles? Alleles are the different forms that a gene can have for a trait. Alleles determine the traits of the organisms Alleles An organism with the same two alleles for a trait is homozygous. An organism with two different alleles for a trait is heterozygous. Therefore: An organism’s genetic makeup is it’s genotype. An organism’s physical makeup is it’s phenotype. Punnett Square The tool used to predict the probability of certain traits in offspring that show the different ways alleles can combine. Punnett Square Dominant allele is Upper case letter =G Recessive allele is Lower case letter =g G G g Gg Gg g Gg Gg Punnett Square Lets try one: Lets cross a true breeding white flower (pp) with a true breeding purple flower (PP). Probability • The branch of mathematics that helps you predict the chance something will happen is called probability • Probability is most often written as a fraction ½ If you roll a pair of dice, what is the probability that you will roll 2 three? Step 1: count the number of faces on a single die. Put this number in the denominator: __ 6 Step 2: Then count how many ways you can roll a three with one die. Put that number in the numerator: 1 6 Step 3: To find the probability of rolling 2 threes multiply 1/6 x 1/6 = 1/36 Genotype Probability Example Use a punnett square to determine the possible genotypes of offspring of a BB x Bb Incomplete Dominance • One trait is not completely dominant over the another. When a plant which is homozygous for red flowers (AA) is crossed with a plant which is homozygous for white flowers (aa), the plants of the F1 generation produce pink flowers which is a blend of red and white condition. This result clearly indicates that neither red flowered condition nor white flowered condition is dominant. Thank You Exit Ticket: Write down one thing they are still confused about regarding genetics.