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Bell Work: Monday February 4, 2013. Go to page 79 in your science notebook: Write a journal about what we did in class yesterday. Discuss some of the traits you did or did not have. On the same page make a “Know and Wanna Know” chart as it pertains to Heredity.
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Bell Work: Monday February 4, 2013 • Go to page 79 in your science notebook: Write a journal about what we did in class yesterday. Discuss some of the traits you did or did not have. • On the same page make a “Know and Wanna Know” chart as it pertains to Heredity. • If you have not taken or completed the test from Wednesday, please see me. • If you have work to turn in, please put it in the drawer for your class. Due today unless you were absent last week.
Heredity • Why don’t you look like a rhinoceros? • The answer to this question seems simple: Neither of your parents is a rhinoceros. • But there is more to this answer than meets the eye. • As it turns out, heredity, or the passing of traits from parents to offspring, is more complicated than you might think. • For example, you may have curly hair, while both of your parents have straight hair. You might have blue eyes while both of your parents have brown eyes. • How does this happen?
Who was Gregor Mendel? • Read pg. 100 • “Who Was Gregor Mendel? • “Unraveling the Mystery” • Gregor Mendel discovered the principles of heredity while studying the characteristics and traits of pea plants. • A characteristic is a feature that has different forms in a population. • For example, hair color is a characteristic of humans. • The different forms, such as brown or red hair is called a trait.
Review Self Pollination and Cross Pollination Pea plants can also cross-pollinate. In cross-pollination, pollen from one plant fertilizes the ovule of a flower on a different plant. There are several ways that this can happen. Pollen may be carried by insects to a flower on a different plant. Pollen can also be carried by the wind from one flower to another. Self pollinating flowers have both male and female reproductive parts. (pistil and stamen). During pollination the sperm (pollen from the anther) attaches to the stigma (sticky opening of the pistil). self pollination creates a true breeding plant.
Mendel studied one characteristic at a time as he worked with these pea plants. • These are some of the plant characteristics that he worked with. Tall? short? Round? Wrinkled? Purple? White?
He was very careful to use only plants that had true breeding for each of the traits he was studying. That way he would know what to expect if they were to self pollinate. He then decided to try cross pollinating with these flowers. He would pull the anther off of one plant and pollinate another plant with it. That way he knew the one flower could NOT self pollinate. He crossed a plant with wrinkled seeds with another plant with round seeds.
Mendel’s First Experiments • One trait was always present in the first generation, and the other trait seemed to disappear. • Mendel chose to call the trait that appeared the dominanttrait. • Because the other trait seemed to fade into the background, Mendel called it the recessivetrait. • The recessive trait for the white flower reappeared in the second generation.
In human terms • Grandma has blue eyes. • Grandpa has brown eyes. • 1st generation: Mom has brown eyes and so do all of her siblings. • 2nd generation: Three out of four of mom’s children have brown eyes. • The other one has blue eyes.
Review: Talk with your group… • What is heredity? • The passing of genetic traits from parent to offspring • Who was Gregor Mendel? • Discovered the principles, or ideas, of heredity • Which trait is present in the first generation? • Dominant trait • Which trait is present in the second generation? • Recessive trait
Review He removed the anther from one plant and then cross pollinated it with another plant. • How did Mendel make sure that the plant didn’t self pollinate? • How many plants out of the first generation were purple? • How many plants out of the second generation were purple? • How many out of the 3rd generation do you think would be purple? http://www.indiana.edu/~p1013447/dictionary/mendel.htm
Traits and Inheritance • Mendel knew from his experiment with pea plants that there must be two sets of instructions for each characteristic. • These instructions for an inherited trait are called genes. • Each parent gives oneset of genes to the offspring. • The offspring then has twoforms of the same gene for every characteristic- one from each parent. • The two forms (often dominant and recessive) of a gene are known as alleles. • Dominant alleles are shown with a capitalletter (P for dominant purple flowers). • Recessive alleles are shown with a lowercaseletter (p for recessive white flowers).
Phenotype & Genotype • Genes affect the traits of an offspring. • An organism’s appearance (the way they look) is known as its phenotype. • In pea plants, possible phenotypes for the characteristic of flower color would be purple flowers or white flowers. • The genotype of an organism is the entire genetic makeup of an organism; the combination of genes for a specific trait. • An organism with two dominant or two recessive alleles is homozygous (same size letters). • An organism with one of each (Pp) is heterozygous.
Punnett Square • A Punnettsquare is used to organize all possible combinations of offspring from particular parents. • Genotype PP is a purebred. • What is the genotype for the offspring to the right? • The dominant allele P ensures that the offspring will have purple flowers. • The recessive allele p may get passed to the next generation. • Why?
Quick Labpg. 107 • Work with your group to complete the Punnett square. • What would be the phenotypes for these offspring? • RR= round seeds • Rr= round seeds • rr= wrinkled seeds R r R r
Probability • The mathematical chance that something will happen is known as probability. • Genotype probability: • Pp x Pp cross has a 50% chance of receiving either allele from either parent. • The probability of inheriting two p alleles is ½x½, which equals ¼, or 25%.
Monohybrid vs. Dihybrid Punnett Square • A monohybrid Punnett square is one where only one trait is crossed. • Example: A tall pea plant TT is crosses with a short pea plant tt. • A dihybrid Punnett square is one where two traits are crossed. • Example: a tall, green flowered plant TtGg is crossed with a short, yellow flowered plant ttgg.
