Bio 111 Study Guide Chapter 14 Genetics BEFORE CLASS: Reading: Read the whole chapter from p. 267-288. It might also be helpful to read before class the Tips for Genetics Problems section on p.290. Definitely review it after class! Definitions: genetics true breeding hybridization P generation F1 generation F2 generation gene allele dominant recessive law of segregation homozygous heterozygous phenotype genotype testcross monohybrid cross dihybrid cross
law of independent assortment multiplication rule addition rule incomplete dominance codominance multiple alleles pleiotropy epistasis polygenic inheritance norm of reaction pedigree carriers Questions/Problems: 1. List at least three human traits that you d like to find out more about how they are inherited. RET Gene Case Study: The RET gene is found on chromosome 10 in humans, with a specific loci (location) shown by the arrow below. The actual gene is 55,000 nucleotide base pairs long. There is a genetic test for mutations of the RET gene, including the V804L mutation. A positive result predisposes the person to several kinds of endocrine cancers (many times of the thyroid). These mutations are inheritable and are often able to be tracked through families by using pedigree charts.
DURING CLASS: Mendel s Experiments Gregor Mendel Experiments Basics Gene Allele Dominant Recessive Homozygous Heterozygous Genotype Phenotype Basic examples Monohybrid cross
1. In humans, the ability to roll the tongue is a dominant trait; the inability to roll the tongue is a recessive trait. If two individuals heterozygous for this trait have a child, what is the chance that the child will not be able to roll his tongue? Testcross 2. In cocker spaniels, black fur (B) is dominant over red (b). If you mate a black cocker spaniel (unknown genotype B_) with a red cocker spaniel (bb) and get red offspring, what is the genotype of the black dog? Dihybrid cross 3. Round seeds (R) are dominant to wrinkled seeds (r) and yellow seeds (Y) are dominant to green seeds (y) in garden peas. What is the expected phenotypic ratio of a cross between RrYy and RrYy individuals?
Mendel s Laws Law of Segregation Law of Independent Assortment Probability in Genetics Multiplication rule 4. If pea plants have round seeds and their genotype is Rr, what is the probability that the gametes will contain a R allele? What is the probability the gametes will contain an r allele? 5. Continuing with the above information, what is the probability that the offspring from two Rr parents will be RR? What is the probability the offspring will be rr? Addition rule 6. Continuing with same information, what is the probability of the offspring being heterozygous, or Rr?
7. What is probability of getting offspring AabbCcDD if both parental genotypes are AaBbCcDd? 8. What is probability of getting the following offspring from parents that are both LlMmNn? A. LLmmNn? B. llmmnn? C. has all 3 dominant traits? D. has all 3 recessive traits? Variations Incomplete dominance 9. Coat color in one breed of mice is controlled by incompletely dominant alleles so that yellow and white are homozygous (YY and WW, respectively), while cream coat color results when individuals are heterozygous (YW). What will be the expected ratios of coat color in the offspring from the cross of two cream individuals? Multiple alleles
Codominance 10. A man with type A blood marries a woman with type B blood. Their child has type O blood. What are the genotypes of these three individuals? What genotypes, and in what frequencies, would you expect in future offspring from this marriage? Pleiotropy Epistasis Polygenic traits Nature vs. Nurture Pedigree Charts
11. Identify whether each pedigree below is displaying a trait that is dominant or recessive. 12. Looking at Figure 14.15a, let s suppose the last couple had another child. What would be the probability that the child will have a widow s peak? RET Gene Case Study: The figure below is a pedigree chart showing the presence of the RET V804L mutation known (so far) in individuals in Mrs. Stewart s family. She is marked as individual A, and she tested positive for the mutation. Do you think this mutation is inherited as a dominant or recessive allele? Mrs. Stewart s daughters are marked as individuals B and C. Mrs. Stewart is heterozygous (Rr) for this mutated allele, and assuming her husband does not have the mutation, what was the chance (in %) that each of her daughters had to inherit the mutation?
RET Gene Case Study (continued): What is the genotype of Mrs. Stewart s Aunt Shirley who is marked D? Do any of Aunt Shirley s children or grandchildren need to be tested for the V804L mutation of the RET gene? Human Genetic Disorders Recessively-inherited: Dominantly-inherited: Genetic counseling and tests: **Take Away Concept** Genetics is one of the most interesting and exciting fields in the biological sciences. More knowledge about how genotypes affect phenotypes, especially when it comes to disease, is being discovered every day!
AFTER CLASS: Questions/Problems: 1. Which of the following terms is not correctly paired with its definition? a. gene: the specific sequence of DNA that codes for one protein b. monohybrid cross: tracks the inheritance of one trait or gene c. allele: the alternate forms of a gene d. phenotype: the actual physical or functional traits of an individual e. homozygous: the organism has two different alleles for a gene 2. For each genotype below, indicate whether it is homozygous (homo) or heterozygous (hetero). aa Bb CC Dd EE ff 3. For each of the following genotypes, identify the correct phenotype. Purple flowers are dominant to white. PP Pp pp Short tails are recessive to long tails. TT Tt tt 4. For each of the following phenotypes, indicate the possible genotypes (pick any letter to use for the alleles). Straight hair is dominant to curly. Straight Curly Pointed heads are dominant to round heads. Pointed Round 5. In humans, widow's peak is a dominant trait, and a straight hairline is a recessive trait. A woman with a widow s peak who is homozygous dominant marries a man with a straight hairline. What would be the possible genotypes of their children and in what percentage? 6. Free earlobes are dominant to attached earlobes in humans. If a man with free earlobes marries a woman with attached earlobes, and they have two kids with free earlobes and one with attached earlobes, can you tell what genotype the father has? How about the two kids with free earlobes?
7. Some dogs have solid colored bodies while others have parti-colored bodies (bodies with areas of white and colored hair). This is not due to codominance, but regular Mendelian dominance. A cross between two solid colored dogs yields one parti-colored female puppy in a litter of six. When she matures and is mated with a parti-colored male, the resulting nine puppies are all parti-colored. Diagram the two crosses and explain the results. 8. For each of the parental genotypes below, identify the possible types of gametes. AaDd Eett NNRr ddgg 9. Short noses (N) are dominant over long noses (n). Detached (or free) ear lobes (A) are dominant to attached ear lobes (a). Cross a homozygous short nosed, homozygous detached ear person with a heterozygous short nosed, heterozygous detached ear person. Show the Punnett square below. What is the probability of getting a child with the genotype NNAA? What is the probability of getting a short nosed, detached ear offspring? 10. In the cross MMnnOoPpQq x mmnnooppqq, what is the probability that that offspring will be a. MmnnOoPPQq? b. MmnnOOPpQq? c. MMnnooppqq? d. Mmnnooppqq? e. all the dominant phenotypes?
11. An example of incomplete dominance in Caucasian humans is the trait of having straight, wavy, or curly hair. A man with wavy hair marries a woman with straight hair. First, what do you think are the genotypes that result in straight, wavy, or curly hair? What percentage of their children might have wavy hair? What percentage might have straight hair? 12. If a man with type AB blood marries a woman with type O blood, what blood types would you expect in their children? What fraction would you expect of each type? 13. Candace has type B blood. Her husband Dan has type AB blood. Is it possible for Candace and Dan to have a child that has O blood? Explain why or why not (use a Punnett square to help if you want). 14. Rachel doesn t have dimples but her brother Steve does. Their parents, Frank and Beverly, both have dimples. Beverly s brother Glen has dimples too. Beverly and Glen s dad Howard has dimples, but their mother Evelyn does not. Glen s wife Charlene doesn t have dimples. They have four kids: Jessica, Melissa, Donald, and Thomas. Melissa and Thomas have dimples, while Jessica and Donald do not. a. Draw the pedigree. b. Write the name of each person below the correct symbol. c. Is having dimples dominant or recessive? d. Write the most accurate genotype you can for each person below their symbol (DD, D_, Dd, or dd).