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Download LAB: Inheritance of Human Traits
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INHERITANCE OF HUMAN TRAITS Heredity can be described as the passing on of traits or characteristics from parent to offspring through chromosomes. A gene is a section on a chromosome that contains genetic information for a single trait. Since genes are randomly distributed into gametes by the process of meiosis, it is not possible to accurately predict the appearance of all traits in offspring. However, it is possible to calculate the probability of an offspring inheriting a single trait. Information contained in genes cannot be seen, therefore, symbols are used to represent the genetic information. A dominant gene hides the appearance of a recessive gene. Dominant traits are represented by a capital letter. Recessive genes are present on the chromosome but the traits are not visible in the organism. Recessive genes are represented by a lower case letter. In order for a recessive trait to be displayed, both alleles for the trait must be recessive. Alleles are different forms of a gene. Some characteristics are neither dominant nor recessive and a blending of traits occurs. The blending of traits is called incomplete dominance. The sex of an organism is determined by the sex chromosomes inherited from the parents. An individual that has two X chromosomes is a female. An individual with an X and a Y chromosome is a male. Since each parent donates one chromosome to every offspring, genes occur in pairs. Critical Terms: 1. Genotype = The genetic make-up of an organism that is represented by letters i.e. BB represents the information contained in the gene 2. Phenotype = The trait seen in an organism i.e. Brown hair 3. Homozygous = Individual who has inherited only dominant or recessive alleles for a trait i.e. BB or bb 4. Heterozygous = An individual the contain a dominant and recessive allele for a trait. i.e. Bb Procedure: 1. Decide which individual in the group will represent the female and the male for each combination of traits. 2. The male should toss the penny on top of the desk. If the coin lands heads up, the offspring is female. If the penny is tails up, the offspring is male. Record your data in the chart. 3. Two pennies should be tossed for the remainder of the traits on the chart. One toss from mom and one from dad. 4. Heads represents donation of the dominant allele and tails represents donation of the recessive allele. 5. Fill in the chart for each trait according to the coin tosses. 6. Draw a picture of your fictitious baby and answer all questions. Hereditary Traits Key Traits Shape of face Cleft in Chin Size of Ears Size of Nose Dimples Shape of Lips Size of Mouth Length of Eyelashes Shape of Eyebrows Position of Eyebrows Size of Eyes Position of Eyes Spacing of Eyes Shape of Eyes Freckles Hair Type Widow’s Peak Dominant (2 Heads) RR Round CC Absent LL Large LL Large DD Present TT Thick LL Large LL Long BB Bushy NN Not Connected LL Large SS Straight EE Close Together AA Almond FF Present HH Curly WW Present Hybrid (One head, One tail) Rr Round Cc Absent Ll Normal Ll Medium Dd Present Tt Normal Ll Medium Ll Long Bb Bushy Nn Not Connected Ll Medium Ss Straight Ee Normal Aa Almond Ff Present Hh Wavy Ww Present Recessive (2 Tails) rr Square cc Present ll Small ll Small dd Absent tt Thin ll Small ll Short bb Fine nn Connected ll Small ss Slanted Upward ee Far Apart aa Round ff Absent hh Straight ww Absent DATA Offspring Results Traits Sex Coin Toss (HH, HT, or TT) H_ Genotype (i.e. RR) X_ Homozygous or Heterozygous Phenotype (i.e. Round) Shape of Face Cleft in Chin Size of Ears Size of Nose Dimples Shape of Lips Size of Mouth Length of Eyelashes Shape of Eyebrows Position of Eyebrows Size of Eyes Position of Eyes Spacing of Eyes Shape of Eyes Freckles Hair Type Widow’s Peak *** DRAW A PICTURE OF YOUR OFFSPRING ON A SEPARATE SHEET OF PAPER*** ANALYSIS 1. What chance did you and your partner have of producing a female offspring? A male offspring? Express your answer as a percentage. 2. Based on the observation of other offspring, were there any offspring with identical traits to your offspring? Explain why this might or might not occur. 3. If a male that is homozygous for widow’s peak (WW) reproduces with a female who is heterozygous for widow’s peak (Ww), what are all of the possible genotypes and phenotypes of their children? 4. If a child has straight hair, what are the possible genotypes of it parents? 5. Explain how it is possible for an offspring to have a trait that is not seen in either of the parents. (i.e., almond eyed parents producing offspring with round eyes) 6. Which traits in this investigation show incomplete dominance? (Reread the opening paragraph) 7. Is it possible to have some genetic traits that were seen in your grandparent but not your parents? Explain. 8. There is a small isolated village in Spain where a large number of people are polydactyl. Polydactyl means having extra fingers or toes. Why does this trait tend to be passed on from generation to generation? 9. Explain how geographic isolation, such as that seen in Spain, can be harmful to the health of an entire species. 10. In some cultures, females can be divorced for not producing male offspring. Based on your knowledge of genetics, explain why this is wrong. Remember who tossed the coin to determine the sex of your offspring. 11. Using Mendel’s Laws, explain why the genotype of any one coin toss does not depend upon the results of another. CONCLUSION The probability of inheriting any given trait is the product of each of the individual probabilities. For example, the probability of having a female offspring is ½ and the probability of having an offspring with a cleft in their chin is ¼. Therefore, the probability of having a female child with a cleft chin is 1/8 (½ X ¼). 1. What is the probability of inheriting a round face? 2. What is the probability of inheriting a square face? 3. What is the probability of inheriting a large nose? 4. What is the probability of having a child with a square head and a large nose? 5. What is the probability of having a female child with a square head and a large nose?