Chapter 2: Mendel’s Principles of Heredity Learning Objectives

Question 1

o Explain Mendel’s law of segregation and how it predicts the 3:1 dominant-to-recessive phenotypic ratio among the F2 generation of a monohybrid cross

Answer 1

 Law of Segregation: Two identical alleles of pure-breeding plants separate (segregate) during gamete formation (so each pollen grain or egg carries only one of each pair of parental alleles)

Question 2

o Relate how Mendel’s experimental approach is similar to the process of modern scientific inquiry

Answer 2

 Wondered how genes were inherited, experimented with garden peas

Question 3

o Explain the importance of Mendel’s inclusion of reciprocal crosses within his controlled breeding program of pea plants

Answer 3

 He reversed the traits of the male and female parents, thus controlling whether a particular trait was transmitted via the egg cell within the ovule or via a sperm cell within the pollen. Because the progeny of these reciprocal crosses were similar, Mendel demonstrated that the two parent contribute equally to inheritance

Question 4

o Interpret phenotypic ratios of progeny to infer how particular traits are inherited

Answer 4

	F2 Phenotypic Ratios:
•	Complementary: 9:7
•	Recessive Epistasis: 9:3:4
•	Dominant Epistasis 1: 12:3:1
•	Dominant Epistasis 2: 13:3
•	Redundancy: 15:1

Question 5

o Analyze human pedigrees to determine whether a genetic disease exhibits recessive or dominant inheritance

Answer 5

 Dominant Traits
• Affected children have at least one affected parent
• Dominant traits show vertical pattern of inheritance/trait shows up in every generation
• Two affect parents can produce unaffected children (if both heterozygotes)
 Recessive Traits
• Affected individual can be children of two unaffected carriers
• All children of two affect parents are affected
• Horizontal pattern

Question 6

o Describe the most common molecular mechanism for recessively inherited human genetic diseases such as cystic fibrosis

Answer 6

 Recessive disease alleles usually specify either no protein or less-functional versions of protein that the normal, dominant allele produces

Question 7

o Predict the type of progeny produced by Mendel’s crosses between pure-breeding plants with discrete, antagonistic traits, such as purple versus white flowers

Answer 7

 Mating of parents with antagonistic traits. Cross-pollination and fertilization between pure-breeding parents with antagonistic traits result in F1 hybrid zygotes with two different alleles.
 Discrete traits- inherited traits that exhibit an either/or status

Question 8

o Cite the most common molecular explanations for dominant and recessive alleles

Answer 8

 Dominant allele encodes a functional product/protein while recessive allele determines either a less functional or nonfunctional version of the protein/no protein at all

Question 9

o Explain why Huntington disease is caused by a dominant allele

Answer 9

 Even when normal protein is present (HD HD+) the abnormal protein damages nerve cells

Question 10

o Describe how Mendel cross-fertilized and self-fertilized pea plants

Answer 10

 Cross-fertilized: brushed pollen from one pea plant onto female organ of another plant (removed anthers from female parents)
 Self-fertilized: pollen is made in anthers, mature pollen lands on stigma (connected to ovaries) pollen grows tube that extends through stigma to ovules

Question 11

o Explain Mendel’s law of independent assortment and how the 9:3:3:1 phenotypic ratio among the F2 of a dihybrid cross provides evidence for this law

Answer 11

 Independent Assortment: random distribution of different genes during gamete formation
 In dihybrid cross, each pair of alleles assort independently during gamete formation; if you cross two traits and one version of each of the two is dominant, then 9:3:3:1 will be the ratio (the 9:3:3:1 table shows that each of the two genes are independently inherited with a 3:1 ratio)

Question 12

o Predict the genotypic and phenotypic ratios among progeny of complex multihybrid crosses using simple rules of probability

Answer 12

 Product Rule: probability of two or more independent events occurring together
 Sum Rule: probability of two or more mutually exclusive events will occur

Question 13

o Distinguish between a monohybrid cross and a testcross

Answer 13

 Monohybrid: crosses between parents that differ in only one trait; they reveal units of inheritance and law of segregation; cross pollination of pure-breeding parental plants make F1 hybrids (all resemble one of the parents)
 Testcross: a way to establish genotype; cross used to determine genotype of individual showing dominant phenotype by mating with individual showing recessive phenotype