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Mendel’s Work. Chapter 3 Section 1 Pg 80-85. Gregor Mendel — the father of genetics. Genetics —the scientific study of heredity Heredity —the passing of traits from parents to offspring. Mendel’s Peas. Mendel could learn a lot from peas because:
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Mendel’s Work Chapter 3 Section 1 Pg 80-85 Gregor Mendel— the father of genetics
Genetics—the scientific study of heredity • Heredity—the passing of traits from parents to offspring
Mendel’s Peas Mendel could learn a lot from peas because: • Pea plants have many traits that exist in only 2 forms such as tall vs short plants, but no medium plants.
Mendel’s Peas Mendel could learn a lot from peas because: • Peas produce a large number of offspring (kids) in each generation
Mendel’s Peas • Normally pea plants self pollinate. This means that pollen from the stamen of a plant enters the pistil of the same plant.
Pollen located on the stamen moves to pistil of the same plant Self-pollination
Mendel’s Peas • Mendel cross pollinated plants. This means that he took pollen from a plant and rubbed it on the pistil of a different plant from which the stamens had been removed (so they couldn’t self pollinate).
Mendel’s Experiments • Purebred—always produces offspring with the same form of a trait as the parent. • Ex. Purebred dogs. Like Cocker spaniels, golden retrievers, Poodles. The opposite is hybrid. This would be a pound puppy
Mendel’s Experiments • In his first experiment Mendel crossed purebred tall plants (they only have tall genes) with purebred short plants (that only have short genes). • Filial (F1) generation—name given to the offspring of the first cross.
? Mendel’s Experiments Mendel cross-pollinated purebred tall plants with purebred short plants and got…. F1 generation Tall plant (breed) short plants P generation (think “parents”)
P generation (think “parents”) F1 generation Mendel’s Experiments All TALL pea plants in the F1 generation….
P generation (cross pollinated) F1 generation (self-pollinated) So we could look at it like this too…
Mendel’s Experiments Results of F2 • Mendel allowed the F1 plants to self-pollinate. • He found that the F2 plants were a mix of tall and short plants in a ration of ¾ tall to ¼ short.
P generation (cross pollinated) F1 generation (self-pollinated) All tall F2 generation ¾ tall and ¼ short
Traits Mendel studied in Pea Plants • Mendel also studied _7_ traits of pea plants: They were : Seed shape, seed color, seed coat color, pod shape, flower position, flower color, and stem height.
Dominant and Recessive Alleles • Pairs—the factors that control each trait exist in pairs. • Female parent—contributes one factor • Male parent—contributes one factor • Together these make a pair
Dominant and Recessive Alleles • Genes—are the factors that control traits. • Genes consist of pairs of alleles. One that comes from the mother parent and one that comes from the father parent.
Dominant and Recessive Alleles • Alleles—the different forms of a gene (such as tall or short, wrinkled or smooth). • Dominant allele—one whose trait always shows up when the allele is present. • Recessive allele—is masked (or covered up) when the dominant allele is present. Recessive alleles only show up if a dominant allele is not present.
dominant dominant recessive dominant recessive recessive EXAMPLES recessive dominant Recessive is the green box and dominant is the black box. Each of your parents has a pair of alleles that they can share. If they only give one… answer the following questions. ? ? ?
EXAMPLES recessive dominant Recessive is the green box and dominant is the black box. Each of your parents has a pair of alleles that they can share. If they only give one… answer the following questions. dominant dominant dominant ? ? recessive dominant ? recessive recessive
EXAMPLES recessive dominant Recessive is the green box and dominant is the black box. Each of your parents has a pair of alleles that they can share. If they only give one… answer the following questions. dominant dominant dominant ? ? recessive dominant dominant ? recessive recessive
EXAMPLES recessive dominant Recessive is the green box and dominant is the black box. Each of your parents has a pair of alleles that they can share. If they only give one… answer the following questions. dominant dominant dominant ? ? recessive dominant dominant ? recessive recessive recessive
Notice • The only time the green box (or recessive allele) could show up is when a black box (or dominant allele) was not present. • This will lead us into punnett squares. recessive recessive recessive
Punnett Squares • So Mendel started out with 2 purebred plants. One was tall and one was short. • Capital T means “tall allele”, lowercase t means “short allel” • But, each of those two plants (tall one and short one) has 2 alleles. They received one from their mother and one from their father.
Options are T(tall) or t(short) • Tall plant was TT –purebred (top of ps) • Short plant was tt—purebred (left of ps) • What would Tt be? A tall/medium/or short plant? • You take this information and put it in a Punnett Square.
. Punnett Square
1st take letters across…. . . . .
In a cross between two purebred plants (TT x tt), the probability of the offspring having the dominant characteristics is 100% (or 4 out of 4 which is the same as 4/4)
But what does it all mean? Represents 4 possible offspring; the probability of children’s height.
Probability is The likelihood that a particular event will occur. Tossing a coin—landing head us is ? The larger the sample size (more tosses of a coin), the closer the actual results predicted by probability.
You said 50%? • Lets go to the virtual coin toss… • http://pbskids.org/cyberchase/games/probability/cointoss.html • What about children. What is the likelihood that a woman would have a boy instead of a girl? • Mendel used probability in genetics.
Mendel and Probability • Mendel was the first person to realize that probability can be used to predict the results of genetic crosses. • In other words he could use probability to “know” that all the offspring of the first generation would be tall… without even seeing them.
Punnett Squares • Can be used to calculate the probability that offspring will have a certain combination of alleles. • Can also be used to predict the probability of an offspring possessing a certain trait. • Get used to this… we will do it a lot.
In a cross between 2 hybrid tall plants (? x ?), the probability of offspring having the dominant characteristic is 75% (or 3 out of 4 or ¾) while the probability of the offspring having the recessive characteristic is 25% (or 1 out of 4 or ¼)
Punnett Square for 2 Hybrid plants to determine height of offspring. What letters should go on the top and to the side? You have to know what hybrid/ heterozygous means.
Punnett Square for 2 Hybrid plants to determine height of offspring. Right! But… What do we do now?
Punnett Square for 2 Hybrid plants to determine height of offspring. We put each allele in a spot on the top and left. It doesn’t matter if the t is above or below the T as long as they are both there.
Punnett Square for 2 Hybrid plants to determine height of offspring. Right! Now you move the alleles over…
Punnett Square for 2 Hybrid plants to determine height of offspring. Right! Now you move the alleles over…and DOWN!!!
Day 2 • REMINDER: Science fair projects are DUE today and tomorrow!
But what does this square mean? First we have to learn about phenotype and genotypes.
Phenotype and Genotype • Phenotype—The physical appearance of the offspring. (ex. Tall or short) • Genotype—The genetic makeup or allele combination of the offspring. • Homozygous (purebred)—2 of the same alleles • TT or tt • Heterozygous (hybrid)—2 different alleles • Tt or tT which are the same thing.
