Investigating Inherited TraitsIntroductionHeredity is the passing on of traits from parent to offspring. The genetic makeup of an individual is knownas its genotype. The physical characteristics of an individual, which are the result of its genotype and itsenvironment, are known as its phenotype.Some alleles are expressed only when the genotype is homozygous. These alleles are said to producerecessive phenotypes. Alleles that are expressed whether the genotype is homozygous or heterozygousproduce dominant phenotypes. An allele that codes for a dominant trait is represented by a capital letter,while an allele that codes for a recessive trait is represented by a lowercase letter. Sometimes when thegenotype is heterozygous, neither the dominant nor the recessive phenotype occurs. In this situation,called incomplete dominance, an intermediate phenotype is produced.In humans, the sex of an individual is determined by the particular combination of two chromosomes calledthe sex chromosomes. Individuals who have two X chromosomes (XX) are females, whereas those whohave an X and a Y chromosome (XY) are males. In this investigation, you will observe how the results ofdifferent allele combinations produce certain traits.ProblemHow are traits inherited?Pre-Lab DiscussionRead the entire investigation. Then, work with a partner to answer the following questions.1. What does a single side of a double-sided coin or disk represent?

2. What is the probability in percent, that a single coin toss will result in heads? In tails?3. Why is tossing a coin a good way to represent allele combinations that occur in nature?

4. For the traits explored in this lab, do all heterozygous pairs of alleles produce an intermediatephenotype?5. Can you accurately determine an organism’s genotype by observing its phenotype? Explain youranswer.Materials (per group)Two (2) coinsProcedure1. Randomly pick your genotype for each characteristic by flipping 2 coins (heads is dominant). Write oneletter in the dad column and one letter in the mom column. For example if you flip one head and onetail, you are heterozygous.2. The first six sets of alleles go in the first homologous chromosomes, the second six go in the nextchromosomes and the last five go in the final chromosomes. The letters under the dad column go in thedad chromosome. Remember, during S phase the DNA replicates, so you will write the letters twice, oneon each side of the X (the sister chromatids). Repeat the process with the mom chromosomes.3. During crossing over the dad and mom chromosomes exchange pieces. Only the inside piece of each Xwill cross over, and only the top and/or bottom portion, not the middle. Cross over your threehomologous chromosomes and write the new sequences in the X’s after the arrow.4. During Meiosis the homologous chromosomes and the sister chromatids separate producing fourgametes with one set of chromosomes. Write the sequence of alleles from each of the threechromosomes in the chromosomes in the gamete (example: the A sister chromatids go in the Agamete).5. With a partner, you will fertilize a gamete. Each partner flips a coin twice. Heads-Heads: gamete A,Tails-Tails: gamete B, Heads-Tails: gamete C, Tails-Heads: gamete D.6. Fill in the line below by describing the phenotype of your child for each trait and on the next page drawthe face, name the child and complete the birth certificate.Phenotypic DescriptionMy baby has ……………………………………………………………………………………………………………………………………………………………………………………………….

Drawing of OffspringDraw a picture of your offspring in the following space:

Analysis and Conclusions1. Describe the gametes that are produced at the end of meiosis comparing them to each other?2. Comparing and Contrasting: How are the end products of meiosis different from those ofmitosis? How are they similar?3. Predicting: Would you predict that another pair of students in your class would have an offspringgenetically identical to yours? Support your answer.4. Drawing Conclusions: Do you think anyone in the world has all the same genetic traits that youhave? Explain the process that accounts for the variation seen in sexually reproducing organisms.

Going FurtherSome inherited diseases cause an individual to die before reaching reproductive age. Using library orInternet resources, read about one of these diseases, and write a brief report about what is understood about its transmission, and in what types of populations it tends to occur. Some examples of inherited diseases that cause early death include Duchenne muscular dystrophy, Tay-Sachs disease, and Krabbe’s disease.

Pedigree Analysis(Who’s your Daddy?)

ObjectiveStudents will solve a family pedigree problem by analyzing and solving family pedigree problems in order tounderstand how traits are passed from one generation to another.Activity 1What is a pedigree?Read the following and answer the questions that follow.A human generation spans more than 20 years, making it almost impossible to carry out the kinds ofexperiments that are possible with other organisms, such as fruit flies. In order to study the inheritance ofhuman traits, biologists have to rely on family histories and medical records to provide the information theyneed. One of the best ways to summarize this information is to construct a pedigree. A pedigree is adiagram that follows inheritance of a single trait through several generations in a family.When analyzing pedigrees, biologists find that certain phenotypes are usually repeated in predictablepatterns from one generation to the next. These patterns are called patterns of inheritance. Individualswho have one copy of a recessive autosomal allele are called carries. Carriers usually do not express therecessive allele, but they can pass it along to their offspring.In a pedigree, squares represent males and circles represent females. Vertical lines connect parents andtheir children, and horizontal lines connect male and female parents. In family symbols for the children areplaced from left to right in birth order, with the oldest child on the extreme left. If a pedigree illustrates aninherited recessive trait, the squares or circles representing males and females with this trait are shaded. Ifa person is heterozygous for the trait (or a hybrid), the square or circle is half shaded.

This pedigree shows the inheritance of anautosomal recessive trait. Pedigrees areparticularly important if the trait is a geneticdisorder and family members wish to know ifthey are carriers or if their children will have

the disorder.

Use complete sentences to answer the following:1. What is a pedigree?

2. When analyzing pedigrees, what do scientists usually find repeating in predictable patterns?3. What are individuals called that have one copy of the recessive autosomal allele?4. In the pedigree example, what shape do they use for male and female?5. What does it mean to be a carrier?6. In the pedigree example, what do the lines connecting the squares and circle mean?

Activity 2Pedigree Practice

1. Pedigree 1 traces the dimple trait throughthree generations of a family. Blackenedsymbols represent people with dimples.Circles represent females and squaresrepresent males.2. The following passage describes the familyshown in Pedigree 1.Although Jane and Joe Smith have dimplestheir daughter, Clarissa does not. Joe’s dadhas dimples, but his mother and sister Gracedoes not. Jane’s dad, Mr. Renaldo, herbrother, Jorge, and her sister, Emily does nothave dimples, but her mother does.

1. Write the name of each person below the correct symbol in Pedigree1. How are marriage andoffspring symbolized? What do the roman numerals symbolize?2. Make a pedigree in the space below, based on the following passage about freckles.Andy, Penny and Delbert have freckles, but their mother, Mrs. Cummins doesn’t. Mrs. Giordano,Mrs. Cummins’s sister has freckles, but her parents, Mr. & Mrs. Lutz do not. Deidra and DarleneGiordano are freckled, but their sister, Dixie, like her father Mr. Giordano, is not freckled.

Evaluating Techniques: What advantages does a pedigree have over a written passage?Summarizing Observations: How does a pedigree organize hereditary information, making it easierto understand?

Activity 3Case StudyAlison was born April 24, 1998. While she was in the nursery, the nurses noticed that her diapers had ablack tint to them even when there was only urine in the diaper. They suspected that she had alcaptonuria.This is a genetic disorder that causes the body to build up homogentisic acid. This acid turns black when itis exposed to the air.Initially this dark urine is the only symptom of alcaptonuria but later in life, connective tissue (bone) oftenbecomes gray or black. There may also be dark spots on the cartilage of the ear and on the white parts ofthe eye (sclera). In middle age, an arthritic condition, especially in the lower back, hips and knees maydevelop and degeneration of the spinal discs may occur.

AssignmentYour job as genetic counselor is to help Alison’s family trace where the gene came from. Alison’s familyneeds help determining who in the family is heterozygous and who is homozygous. Write out a possiblepedigree on your own paper.This genetic disorder follows Mendel’s rules:AA-free of disease; Aa-carrier (free of the disease); aa-has alcaptonuria.Who is in the pedigree?The pedigree should include the following people:Paternal Grandfather (PGF)Paternal Grandmother (PFM)Maternal Grandfather (MGF)Maternal Grandmother (MGM)Mother (M)Father (F)Maternal Aunt (MA)Maternal Uncle (MU)Paternal Aunt (PA)Paternal Uncle (PU)Brother (B)Alison (A)