UNIT THREE: BIOLOGY HEREDITY

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1 DO NOW Quietly and without getting out of your seats, look around at your classmates. Note how they vary in the shape of the front hairline (widow s peak vs. straight hairline), the space between the two upper front teeth (gapped vs. ungapped front teeth), and the way in which the earlobes are attached (attached vs. free earlobes). Make a list of the different forms of these traits that you have observed in the class. Could these traits be inherited? If so, from whom? Is it possible that these traits could be found in a person and his or her biological grandparents, but not in the biological parents? UNIT THREE: BIOLOGY HEREDITY VOCABULARY REVIEW Write down the following terms in your notebook, and write the definitions of each: Genetics Heredity P 1 Generation F 1 Generation Dominant trait Recessive trait HEREDITY In the middle 1800s, an Austrian monk named Gregor was interested in learning how characteristics are passed from parents to. To investigate this question, Mendel bred plants because he

2 could study them easily. At that time, scientists had concluded that an organism passes its on to its offspring. No one, until, had established how this happened. GENETICS AND HEREDITY The field of that investigates how characteristics are transmitted from parents to offspring is called. Mendel s work with plants formed the basis of genetics. His results explained how operates. is the transmission of characteristics from parents to offspring. Mendel studied characteristics of pea plants. Each characteristic occurred as one of two contrasting traits. Plant Pod color Pod appearance Seed Seed Pea Plant Characteristics Tall stem or Short stem Green or Inflated or Constricted or Wrinkled Yellow or position on stem Flower color Axial (long stem) or Terminal (on top of stem) or White

3 Pea Plant Characteristics MENDEL S EXPERIMENTS Mendel collected the seeds from pea plants and them. Mendel recorded the that appeared when the plants grew to maturity. Mendel was initially by his observations. Ex: He observed that the seeds from plants produced both tall and short plants. Ex: He observed that the seeds from purple-flowering plants produced both plants with flowers and plants with white flowers. Mendel then designed experiments to explain these observations. Mendel studied each of these traits. He did this by controlling how the plants. He any possibility that birds, insects, or the wind could carry pollen from one plant to another. Mendel then bred plants that were for each trait. Let s look at an example: Mendel developed plants that were pure for stems and plants that were pure for stems. When two plants that were pure for tall stems were bred,

4 they would only produce plants that had stems. All of the plants were identical for the other six characteristics, such as pod color and seed texture. Mendel eventually obtained lines of pure plants, one for each of the 14 traits. Once Mendel was satisfied that his plants were pure for a particular trait, he performed a (x) by transferring the pollen from one type of plant to another type of plant. He performed crosses for all seven traits (see below). tall stem x stem pod x yellow pod pod x constricted pod smooth seed x seed seed x green seed axial flower x terminal flower purple flower x flower MENDEL S OBSERVATIONS All of the plants in the crosses listed are known as plants. Mendel labeled each of these parental plants as the generation. The offspring of the P 1 generation is the generation. Mendel noticed that all the plants in the F 1 generation displayed only of the traits present in one of the P 1 generation plants. Ex: In crosses between plants with tall stems and plants with short stems, all the plants in the F 1 generation had stems. Ex: Crossing plants with yellow seed color and plants with green seed color produced F 1 plants that all had seeds. How is this possible?

5 Mendel concluded that one trait for each characteristic the expression of the other trait. Mendel suggested that one of the traits was controlled by a factor that overrides (dominates) the other factor. Ex: Mendel determined that tall stems were a trait. Mendel then determined that the trait that did not appear in the F1 generation was controlled by a factor. Ex: Mendel called short stems a trait characteristic that is by a dominant trait. If one parent has genetic material for a dominant trait and the other parent has genetic material for a recessive trait, their offspring will have the trait of the first parent. A dominant trait appear whether or not the recessive trait is present. A recessive trait only appears when the dominant trait is. An offspring needs to inherit copies of the genetic material for a trait in order for that trait to. Both parents have to be of a recessive trait in order for an offspring to that trait. This table summarizes Mendel s conclusions about which traits in pea plants were dominant and which traits were recessive: Dominant Trait stem pods Inflated pods Smooth seeds seeds Axial flowers Purple flowers Recessive Trait Short stem Yellow pods Constricted pods seeds Green seeds Terminal flowers flowers