Chapter 7 Growth and Inheritance Lesson 2: How Are Characteristics Inherited?

Vocabulary Preview Inherited trait: a characteristic passed from parents to their offspring Dominant trait: a trait that appears even if an organism has only one factor for the trait Recessive Trait: a trait that appears only if an organism has two factors for the trait Gene: the part of a chromosome that contains the DNA code for an inherited trait

Questions to think about! Do living things pass on traits? What kinds of traits do humans have in common?

Inherited Characteristics Lab Procedure: Steps to Follow 1. Complete the following table like the one shown. 2. Stick out your tongue and try to roll its edges up, toward the middle. 3. Use your partner to help you make your observation. Record your results. 4. Use your partner to help observe the shape of your earlobes. Are they attached to your face or do they hang free? Record your results. 5. Fold your hands in front of you. Observe which of your thumbs falls naturally on top. Record your results. 6. Use your partner to help observe whether you have a widow’s peak or not. Record your result.

Characteristic Result: (Circle One) Class Totals Tongue Rolling Yes No Earlobes Attached Free Folded Hands Left Right Widow’s Peak

Draw Conclusions 1. Which traits in each pair occurred more often in your class? 2. Do you think these characteristics are inherited or learned? http://www.sln.org/guide/knox/Traits/traitsexamples.pdf

How Characteristics are Inherited? You may have a friend who looks a lot like her parents. She may share her mother’s eye color and dimples or have the same hair and skin type as her father. These and many other traits are inherited. An inherited trait is a characteristic passed from parents to their offspring.

How Characteristics are Inherited? In humans, hair color, eye color, and skin color are inherited. Freckles, hair texture, and earlobe shape are also inherited. So are some behaviors ex. The tendency to be right/left handed In animals, eye color, fur color, texture is inherited.

How Characteristics are Inherited? Each of the puppies inherited some traits from its parents, including facial shape and hair texture. For many years, farmers have selected animals through breeding. They’ve bred animals having some desirable with animals having other desirable traits so that the offspring would have these traits too.

Dominant and Recessive Traits Gregor Mendal an Austrian monk did hundreds of experiments and kept careful records of his results. He found that first-generation offspring of tall plants and short plants were tall, but second-generation offspring included about one-fourth short plants. He hypothesized that the first-generation plant must have a hidden factor for shortness. How else could this trait appear in the second generation?

Dominant and Recessive Traits In pea plants, tallness is a strong trait, or a dominant trait. If an organism has one factor for a dominant trait, that trait appears. Shortness in pea plants is a weak trait, or a recessive trait. A recessive trait appears only if an organism has two factors for the trait. If both a dominant factor and a recessive factor are present, the dominant trait appears. This explains why three-fourths of Mendel’s second generation pea plants were tall.

Dominant and Recessive Traits Plants with one or two factors for tallness were tall. Plants with two factors for shortness were short. Ex: Fur color in mice. 3 of the offspring are dark brown, and one is light brown. Both parents have dark brown fur which is dominant. For light brown fur to appear, both parents must have a factor for light brown fur.

You can use a Punnett Square to predict the traits that offspring will show. In mice, dark brown fur is dominant. Dominant factors in the square are capital letters. Here, B is the factor for dark brown fur, and b is the factor for light brown fur. One parent’s factors are shown at the top of the square, and the other parent’s factors are shown at the left of the square. You can predict the fur color of the offspring by pairing each factor from one parent with each factor from the other parent.

Dominant and Recessive Traits In humans, having blue eyes is a recessive trait. Can two brown-eyed parents have a child with blue eyes? Yes, but they must both have a hidden factor for blue eyes.

Dominant and Recessive Traits The ability to roll your tongue is a dominant trait. If you can roll your tongue, you inherited either two dominant factors (one from each parent) or one dominant factor and one recessive factor. If you aren’t able to roll your tongue, you inherited two recessive factors (one from each parent).

Dominant and Recessive Traits Unattached earlobes are dominant, and attached earlobes are recessive. If your earlobes are unattached, you inherited at least one dominant factor. If you have attached earlobes, you inherited two recessive factors.

Dominant and Recessive Traits Even though right-handedness is dominant, most people rest the left thumb on top when they fold their hands. Resting the left thumb on top is dominant. If you rest your right thumb on top, what factors did you inherit?

Genes Today Mendel’s factors are known to be different forms of genes. A gene is the part of a chromosome that contains the DNA code for an inherited trait. DNA is a chemical that provides detailed instructions to the cell about every function of life. Ex: It directs the cell to divide to make more cells and to perform various other functions http://www.sonic.net/~nbs/projects/bio115l/form.html

Genes A gene for a particular trait is found at a specific place on a chromosome. All inherited traits-tongue rolling, thumb position, hair color are controlled by genes. You are genetically unique. You share some characteristics with most humans, but unless you have an identical twin, there is no one else with exactly the same combination of genes that you have.

Genes What makes you different from everyone else? Remember that during meiosis, each gamete gets only one half the chromosomes of a body cell. So each of your parents contributed half of his/her genes to you. You inherit over 30,000 different genes which makes you unique.