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Heredity and Reproduction Chapter 4 Reference Text: PCI LIFE SCIENCE

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Chapter 4 - Section 1 TRAITS

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TRAITS Have you ever heard someone say something like, "You have your mother's eyes, or "You have your father's chin"? Why do you resemble your parents?

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TRAITS The color of your eyes is a trait. Traits are the physical characteristics that an organism possesses. Parents pass on their traits to their children (offspring). This is called heredity.

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TRAITS What determines which traits you inherit from each parent?

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Mendels Pea Plants In the 1800s, a scientist named Gregor Mendel studied the passing of traits from parents to offspring. He wanted to know why certain patterns showed up in living things.

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Mendels Pea Plants Mendel had noticed that a certain trait would appear in one generation but not in the next. Then, the trait would show up again in the next generation. For example, a man would have curly hair, his child would have straight hair, and his grandchild would have curly hair.

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Mendels Pea Plants Mendel wanted to know why this happened. He wondered how traits passed from parents to offspring.

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Mendels Pea Plants Mendel did some experiments to find out. He decided to cross-pollinate pea plants and see what happened.

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Mendels Pea Plants Cross-pollination happens when pollen from one is transferred to the reproductive structure of another plant. The parent plants will produce a new plant.

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Mendels Pea Plants Cross-pollination can happen when an insect sits on a flower and pollen sticks to the insect. When the insect flies to another flower, it deposits the pollen from the first flower onto the reproductive structure of the second flower.

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Mendels Pea Plants

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Mendel conducted his experiments with pea plants because they grow quickly and there are a lot of different kinds of pea plants.

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Mendels Pea Plants For example, pea plants can be short or tall, can have round or wrinkled seeds, and can have purple or white flowers.

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Mendels Pea Plants In Mendel's experiments, he cross- pollinated plants that had different traits to see what the offspring would look like. For example, Mendel wanted to know what would happen if a tall plant and a short plant had offspring. Would the offspring be tall, short, or medium? What do you think?

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Mendels Pea Plants If a plant with purple flowers is cross-pollinated with a plant with white flowers, what color will the offspring's flowers be? Mendel studied seven characteristics of pea plants. He wanted answers to the following questions: If a plant with yellow seeds is cross-pollinated with a plant with green seeds, what color will the offspring's seeds be? If a plant with round seeds is cross-pollinated with a plant with wrinkled seeds, what shape will the offspring's seeds be? If a plant with green pods is cross-pollinated with a plant with yellow pods, what color will the offspring's pods be?...and so on

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Chapter 4 - Section 2 Dominant and Recessive Traits

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Mendels Pea Plants Gregor Mendel cross-pollinated pea plants to study the characteristics of their offspring, For example, he cross- pollinated tall plants with short plants. These plants are called the parent generation (P). Their offspring are called first-generation (F1) plants.

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Mendels Pea Plants In Mendel's experiment, all of the first-generation plants were tall. What happened to the short trait? Would all the offspring always be tall?

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Dominant & Recessive Traits The same results happened in every experiment. One trait, like being tall, was always there in the first generation. The other trait, like being short, seemed to go away.

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Dominant & Recessive Traits He described the trait that went away in the first generation as the recessive trait. Mendel described the trait that was there in the first generation as the dominant trait.

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Dominant & Recessive Traits A dominant trait is a trait that is most likely to appear in offspring and a recessive trait is least likely to appear in offspring.

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Dominant & Recessive Traits If green pod color is the dominant trait and yellow pod color is the recessive trait, what will the pod color of the F1 generation offspring have? If you said GREEN, you are correct!

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Dominant & Recessive Traits Mendel wanted to know what happened to the recessive traits. So, he watched what happened when the first- generation plants reproduced. Their offspring were called second-generation plants. (F2)

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Dominant & Recessive Traits Mendel noticed that the recessive traits came back in some of the offspring. Most of the second-generation plants were tall, but some were short.

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Dominant & Recessive Traits This happened with every set of traits that Mendel studied. Each recessive trait reappeared in some of the second-generation plants.

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Dominant & Recessive Traits Mendel figured out that each plant had two sets of instructions for each characteristic.

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Dominant & Recessive Traits These instructions are called genes. Genes are the parts of DNA that give instructions for what traits offspring will have.

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Dominant & Recessive Traits Each parent gives one set of genes to the offspring. The offspring has two forms of the same gene for each characteristic. Each member of a gene pair is called an allele.

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Genotype and Phenotype The combination of alleles in an organism controls what traits the organism will have. For example, there is one allele for shortness in pea plants and one allele for tallness. If the offspring's gene for height is made up of two alleles for tallness, the plant will be tall. If the offspring's gene for height is made up of two alleles for shortness, the plant will be short

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Genotype and Phenotype This combination of genes passed on to offspring is called genotype. Dominant alleles are written as uppercase letters. So, the genotype for a plant with two dominant alleles for height is TT. Recessive alleles are written as lowercase letters. So, the genotype for a plant with two recessive alleles for height is tt. TT tt

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Genotype and Phenotype If an organism has one dominant allele for height and one recessive allele for height, its genotype is Tt.

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Genotype and Phenotype Phenotype is the way an organism looks. An organism's phenotype is decided by its genotype.

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Genotype and Phenotype If a dominant allele is present in the organism's genotype, that trait will appear in the organism. If a plant has one dominant allele for height, the plant will be tall. A recessive allele is hidden if a dominant allele is present.

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Genotype and Phenotype An organism will only display a recessive trait when two recessive alleles are present and there are NO dominant alleles.

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Genotype and Phenotype Imagine that two pea plants are cross- pollinated. One pea plant has the genotype TT, so it is tall. The other pea plant has the genotype tt, so it is short.

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Genotype and Phenotype Because the allele for tallness (T) is dominant, a plant with the genotype TT or Tt will be tall. Remember, a recessive allele is hidden if a dominant allele is present. Offspring with the genotype tt have two recessive alleles. These offspring will be short.

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Punnett Squares Biologists use a diagram called a Punnett square to figure out the probability of an offspring expressing a certain genotype. Probability is the mathematical chance that something will happen.

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Punnett Squares Look at the Punnett square below. One parent's genotype for height is recorded on the top row (TT). The other parent's genotype for height is recorded in the left column (tt). TT t t

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Punnett Squares Remember that a child gets one allele from each parent. MOMDAD TT t t

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Punnett Squares The four examples in the Punnett square show what will happen if the two parents have offspring. In this case, every combination of alleles from the two parents results in the genotype Tt. So, 100 percent of the offspring will be tall. TT t t T t

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Punnett Squares What happens when one of the parents has a dominant allele and a recessive allele? Tt t t

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Punnett Squares Look at the Punnett square below. In this case, two offspring have the genotype Tt and two have the genotype tt. Two offspring will be tall, and two will be short. Tt t t T t t T t t

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Punnett Squares What happens when both parents have a dominant allele and a recessive allele? Tt T t

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Punnett Squares Look at the Punnett square below. In this case, one offspring has the genotype TT, two have the genotype Tt, and one has the genotype tt. How many of the offspring will be tall, and how many will be short? Tt T t T T t t

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Traits in Humans A combination of alleles makes you look the way you do. You get traits from your parents, just like pea plants do.

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Traits in Humans For example, the trait of earlobe shape in humans is inherited. There is an allele for free earlobes and an allele for attached earlobes. The allele for free earlobes is dominant, and the allele for attached earlobes is recessive. Free Earlobes Attached Earlobes

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Traits in Humans If your gene for earlobes is made up of two alleles for free earlobes, you will have free earlobes. If you have two alleles for attached earlobes, you will have attached earlobes. If you have one allele for attached earlobes and one allele for free earlobes, what will your earlobes look like?

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Traits in Humans The characteristics of all organisms are controlled by the alleles that make up their genes. Have you ever looked at a newborn baby and noticed that it resembles its parents? You are observing the effects of alleles.

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Traits in Humans Alleles determine who has a cleft chin, curly hair, blue eyes, and many other physical characteristics.

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Chapter 4 - Section 3 Heredity & Reproduction