Guiding Questions
Gregor Mendel’s Discoveries
- Explain how Mendel’s particulate mechanism differed from the blending theory of inheritance.
- Define the following terms: true-breeding, hybridization, monohybrid cross, P generation, F1 generation, and F2 generation.
- List and explain the four components of Mendel’s hypothesis that led him to deduce the law of segregation.
- Use a Punnett square to predict the results of a monohybrid cross, stating the phenotypic and genotypic ratios of the F2 generation.
- Distinguish between the following pairs of terms: dominant and recessive; heterozygous and homozygous; genotype and phenotype.
- Explain how a testcross can be used to determine if an individual with the dominant phenotype is homozygous or heterozygous.
- Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic and genotypic ratios of the F2 generation.
- State Mendel’s law of independent assortment and describe how this law can be explained by the behavior of chromosomes during meiosis.
- Use the rule of multiplication to calculate the probability that a particular F2 individual will be homozygous recessive or dominant.
- Given a Mendelian cross, use the rule of addition to calculate the probability that a particular F2 individual will be heterozygous.
- Use the laws of probability to predict, from a trihybrid cross between two individuals that are heterozygous for all three traits, what expected proportion of the offspring would be:
- homozygous dominant for the three traits
- heterozygous for all three traits
- homozygous recessive for two specific traits and heterozygous for the third
- Explain why it is important that Mendel used large sample sizes in his studies.
Extending Mendelian Genetics
- Give an example of incomplete dominance and explain why it does not support the blending theory of inheritance.
- Explain how phenotypic expression of the heterozygote differs with complete dominance, incomplete dominance, and codominance.
- Explain why Tay-Sachs disease is considered recessive at the organismal level but codominant at the molecular level.
- Explain why genetic dominance does not mean that a dominant allele subdues a recessive allele. Illustrate your explanation with the use of round versus wrinkled pea seed shape.
- Explain why dominant alleles are not necessarily more common in a population. Illustrate your explanation with an example.
- Describe the inheritance of the ABO blood system and explain why the IA and IB alleles are said to be codominant.
- Define and give examples of pleiotropy and epistasis.
- Describe a simple model for polygenic inheritance and explain why most polygenic characters are described in quantitative terms.
- Describe how environmental conditions can influence the phenotypic expression of a character. Explain what is meant by “a norm of reaction.”
- Distinguish between the specific and broad interpretations of the terms phenotype and genotype.
Mendelian Inheritance in Human
- Explain why studies of human inheritance are not as easily conducted as Mendel’s work with his peas.
- Given a simple family pedigree, deduce the genotypes for some of the family members.
- Explain how a lethal recessive allele can be maintained in a population.
- Describe the inheritance and expression of cystic fibrosis, Tay-Sachs disease, and sickle-cell disease.
- Explain why lethal dominant genes are much rarer than lethal recessive genes.
- Give an example of a late-acting lethal dominant gene in humans and explain how it can escape elimination by natural selection.
- Define and give examples of multifactorial disorders in humans.
- Explain how carrier recognition, fetal testing, and newborn screening can be used in genetic screening and counseling.
