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HUMAN INHERITANCEINTRODUCTION

Humans inherit traits in the same manner as other organisms. Within each cell of your body are structures called chromosomes that contain thousands of genes responsible for specific traits. Many of these traits are complex and are the results of several genes working together. By applying the laws of heredity and probability, biologists have been able to gain a better understanding of many human traits.

In this activity, you will observe several of your own traits. You will determine your phenotype and predict your genotype for the traits. You will assume that each pair of the traits observed is the results of a single pair of genes.

OBJECTIVE

After completing this lab, you will be able to explain how expressed traits are passed from parent to offspring and how sorting and recombination of genes during sexual reproduction have an affect on variation in offspring.

MATERIALS

pennyPTC papercolored pencils or crayons

PROCEDURE

Part I. Observing Human Traits

Listed below are 12 different human traits. With the help of a partner, observe the following traits in yourself and record your observation in Table 1. Use the letters given for each trait when recording your genotype. If you exhibit the recessive phenotype, your genotype for that trait is homozygous recessive. Therefore, you should record your genotype as a pair of recessive genes, for example, “aa.” If you express the dominant trait, record your possible genotypes, “AA” or “Aa,” since you cannot tell at the moment if you are homozygous or heterozygous for the trait.

1. Eye color is controlled by several pairs of genes; however, people who have blue eyes are homozygous recessive, bb, for the eye color trait. People who have brown, hazel, or green eyes are either homozygous dominant, BB, or heterozygous, Bb, for the trait.

ATTACHED EARLOBES (ee) FREE EARLOBES (EE or Ee)

THE ABILITY TO ROLL ONE’S TONGUE IS GENETIC. IF YOU CAN DO IT, YOU ARE EITHER RR OR Rr. IF YOU CANNOT ROLL YOUR TONGUE, YOU WILL NEVER BE ABLE TO DO IT – YOU ACTUALLY LACK THE NECESSARY MUSCLES.

WIDOW’S PEAK (WW OR Ww) STRAIGHT HAIRLINE (ww)

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2. People may have ears with the earlobes attached directly to the side of the head or ears that are fee with a space between the earlobe and the side of the head. Free earlobes are dominant, EE or Ee, while attached earlobes are recessive, ee.

3. Some people have the ability to roll their tongues into a U-shape when the tongue is extended from the mouth. This is a dominant trait, RR or Rr. The recessive expression, rr, is present when people cannot roll their tongues.

4. A hairline that comes to a peak in the middle of a person’s forehead is called a “widow’s peak” and is a dominant trait, WW or Ww. A straight hairline is the result of a pair of recessive genes, ww.

MID-DIGITAL HAIR (HH OR Hh)

CURLY HAIR (CC OR Cc) STRAIGHT HAIR (cc)

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5. A dominant gene, H, results in the growth of hair on the middle joint of a person’s fingers or toes (called mid-digital hair). People who are homozygous recessive, hh, will not have hair on the middle joints on their fingers. (You may only have one hair on one of your middle digits, so look carefully.)

6. Some people can taste the chemical, phenylthiocarbamide, or PTC. The ability to taste is determined by the presence of the dominant gene, T. People with the homozygous recessive genotype, tt, cannot taste PTC at all.

7. In people, curly hair, CC or Cc, is dominant to straight hair, cc.

8. A chin cleft is a dominant expression determined by the gene, A. Lack of a cleft means that a person has a pair of recessive genes, aa.

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9. In people, dark hair is dominant to light hair. A person with dark hair would have the dominant gene, D, whereas a person with light hair would have a pair of recessive genes, dd.

10. Polydactyly , the condition of having extra fingers, is a dominant expression in people. Polydactyly is produced by the dominant gene, P, while the “normal” five fingers is produced by a pair of recessive genes, pp.

11. Skin freckles are the results of a dominant gene, F. The lack of freckles is the result of a pair of recessive genes, ff.

12. Dimples are the result of a dominant gene, D. The lack of dimples is the result of a pair of recessive genes, dd.

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TABLE 1PHENOTYPES AND GENOTYPES OF SEVEAL HUMAN TRAITS

# TRAIT PHENOTYPE GENOTYPE(S)If you express the dominant

phenotype write both possibilities

1 Eye color

2 Earlobes

3 Tongue rolling

4 Hairline

5 Mid-digital hair

6 PTC tasting

7 Hair type

8 Chin cleft

9 Hair color

10 Polydactyly

11 Skin freckles

12 Dimples

Part 2: Predicting the Phenotypes of Offspring

Knowing your genotype and phenotype for various traits can help you to determine the traits that your offspring will have. For example, if you have blue eyes and marry a person with brown eyes, what are the chances that your children will have blue eyes?

1. For each trait in Table 2, determine if you have the dominant or recessive phenotype. If you have the recessive phenotype, record the recessive gene in the “Your Gene” column. If you have the dominant phenotype, assume that you are heterozygous. You will need to flip a penny to determine which gene you pass on to your offspring – heads = dominant gene; tails = recessive gene. Record the gene in the “Your Gene” column.

2. In the “Baby’s Genotype” column, record the genotype of your potential baby for each trait and then determine the phenotype of your baby. Your fictitious mate’s genes are provided for you.

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TABLE 2PREDICTING THE PHENOTYPES OF OFFSPRING

* (connected) unibrow separated ** albino

++ broad lips +++ thin lips

TRAIT DOMINANT PHENOTYPE/GENE

RECESSIVE PHENOTYPE/

GENE

Your Geno-type(2 letters)

Your Gene

(1 letter)Mate’s Gene

Baby’sGeno-type

(2 letters)

Baby’s Pheno-type

(word)hair color dark B light b bhair texture curly or wavy T straight t twidow’s peak yes W no w Whead shape oval O other o Oskin color present S albino ** s Sfreckles yes F no f Fdimples yes D no d deye color brown/green E blue, gray e eeye shape round R other r Reyebrows * separated X connected x Xearlobes free A attached a aear wiggling can U cannot u ushape of nose straight Z curved z zlip size broad ++ H thin +++ h htongue rolling can C cannot c cchin cleft yes J no j j

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ANALYSIS

1. After recording your genes in Table 2 and determining the genes your baby will have, flip a coin to determine the gender of the baby – heads = boy, tails = girl.

2. Complete the summary paragraph by filling in the blanks and circling the appropriate choice within the parenthesis.

My offspring (will or will not) have dimples on (his or her) ________- shaped head.

(He or she) will have (dark or light) (curly or straight) hair. My baby (will or will not)

have a widow’s peak. (He or she) will have bright, sparkling eyes, ________ in

color, under (one or two) eyebrows. Between the eyes will be a nose with a

_________ slope; and below the nose, there will be two (broad or thin) lips. (He or

she) will also have ears with (attached or free) earlobes. My baby will have a chin

(with or without) a cleft. It will be fun to teach my child to stick out (his or her) tongue

which (he or she) (can or cannot) roll. May baby definitely (will or will not) be cute.

3. Using colored pencils or crayons, draw a picture of your baby’s face in the frame below. Include at least ten traits from the paragraph above and/or Table 2. The title of your drawing should be the name of your pretend baby. Label the traits you have drawn.

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4. Is it possible for your baby to have the same genotypes as another pretend baby in the room? Why or why not?

5. This lab examines only facial characteristics. As the number of traits increases, what happens to the probability that two individuals will be identical? Use math to justify your answer.

EXTENSION

Use the information from the “Human Inheritance” lab to answer the following questions. Use Punnett squares to support your answers.

1. Fernando is unable to wiggle his ears, but both of his parents can. Explain how this is possible.

2. Katie has normal skin pigmentation, but her mother has albinism, a condition in which hair, skin, an eyes do not have any pigmentation. Katie married Kent who also has normal skin pigmentation. What is the probability that Katie and Kent will produce an albino child?