Answers to Lab 3 Critical Thinking Questions

1. Law of segregation: Mendel recognized that traits are controlled by distinct units. Our modern understanding of sexual reproduction and meiosis confirms that genes appear separately in the sex cells of the parents and are brought together in the offspring. Law of independent assortment: Mendel noticed that the pea plant traits were often inherited separately from one another. Our modern understanding of meiosis confirms that genes on nonhomologous chromosomes are sorted independently in gametes.

2. Timmy was homozygous dominant for trait F. Looking at the Punnett square for his parents’ mating (Mom and Dad both Ff), what was the probability of Timmy having a different genotype? What was the probability of Timmy having a different phenotype?

Different genotype = 75% chance (50% chance of Ff; 25% chance of ff)

Different phenotype = 25% chance (25% chance of recessive phenotype)

Timmy’s mother was heterozygous for trait F. Looking at the Punnett square for the grandparents’ mating (Grandpa FF and Grandma ff), what was the probability of Timmy’s mother having a different genotype? What was the probability of Timmy’s mother having a different phenotype?

Different genotype = 0% chance; different phenotype = 0% chance

3. The complete chart is as follows:

Shows Real Individuals X (parents) X (all people)

Shows Potential Individuals X (an offspring)

4. Answers will vary, depending on students’ analysis of themselves for the five Mendelian traits in Exercise 5 (cleft chin, freckles, attached earlobes, hitch-hiker’s thumb, and widow’s peak). For unclear genotypes, students are to collect phenotypes of parents and siblings to help elucidiate them Note: This question could be modified to ask students to actually create the appropriate pedigree diagram for each of the traits in question.

5. No, in the the dihybrid cross in Exercise 8 inheriting one trait did not necessarily impact the inheritance of the other. There was a 50% chance that Suzy and Jose’s child would have freckles. Of that, there was an equal likelihood of the child having or not having a widow’s peak. This demonstrates that Mendel’s law of independent assortment was correct. The two traits are inherited separately, and one trait does not necessarily impact the inheritance of the other. Note: This question could be completed as part of Exercise 8.

6. Yes, it is possible that Max is the father of this litter of puppies. Based on the pedigree information (see diagram), it is possible that both Max and Stella are heterozygous (Nn) for