Genetics Chapter 3 Quiz

Teaching Assistant Office Hours

• Office hours are held Monday-Wednesday evenings in FEA 141.
• Genetics TAs:
  • Monday: 6:00 PM - 8:00 PM - Hannah Kotek
  • Tuesday: 6:00 PM - 8:00 PM - Hannah Kotek
  • Wednesday: 6:00 PM - 8:00 PM - Ashley Lee
  • Thursday: 6:00 PM - 8:00 PM - Ashley Lee
• Additional TA:
  • Hannah Kotek
• Students can drop by for study tips, strategies, and other genetics assistance.

Mendelian Analysis & Probabilities

• Mendelian Analysis:
  • Mendel's pea plant crosses
  • Law of Segregation
  • Law of Independent Assortment
• Probabilities Review:
  • Product rule
  • Sum rule

Practice Problems

• Chapter 3:
  • Single-gene analysis problems: 4th edition (14, 15, 16, 17, 18, 19, 29, 30, 40); 5th-7th edition (14, 16, 17, 18, 20, 21, 31, 33, 43)
• Problems are provided to help with understanding the material
• No need to turn in the practice problems listed here
• A separate problem set will be assigned for a grade and cover material from multiple lectures (~10 problems)

Test Crosses

• Used to determine the genotype of a phenotypically dominant individual
• Cross with an individual with a known recessive phenotype
• Test for hidden recessive genes with homozygous recessive tester strain
• Phenotype of progeny from test cross indicates the genotype of the tested parent

Test Crosses (Continued)

• A test cross helps determine the alleles carried by the F1 parent.
• The recessive allele is solely contributed from the test-cross parent.
• The resulting phenotypes of the progeny indicate the F1 parent's genotype.
• Example: Yellow pea (F1): Is it YY or Yy? Cross it with a yy pea (test cross) to determine genotype.

Expected Results of a Test Cross

• Yellow peas are dominant to green peas
• Heterozygous Yellow Pea:
  • Yy X yy (tester)
  • Expect 50% Yy (yellow) and 50% yy (green) progeny
• Homozygous Yellow Pea:
  • YY X yy (tester)
  • Expect 100% Yy (yellow) and 0% yy (green) progeny
• Works for all 7 of Mendel's chosen traits (and many others)

Mendel Followed Two Genes at Once

• Consider two traits for pea color and shape:
  • Y (yellow) and y (green)
  • R (round) and r (wrinkled)
• Example problem involving a true breeding plant with round, green seeds crossed with a true breeding plant with wrinkled, yellow seeds.

Tracking Two Genes

• Pure-breeding parentals
• F1 are all RrYy (round, yellow)
• Observed 9:3:3:1 ratio in F2 generation (round yellow, round green, wrinkled yellow, wrinkled green)

Dihybrid Cross

• Parents are heterozygous for two traits
• Each dihybrid plant produces 4 gamete types
• Example: YyRr → YR, Yr, yR, yr (equal frequency)

Punnett Square of a Dihybrid Cross

• F1 produces 4 different gamete types in equal proportions
• Gametes combine at random to form zygotes
• Example Punnett square for a dihybrid cross of RrYy x RrYy

Mendel's Second Law

• Law of Independent Assortment:
  • Segregation of alleles of two different genes is independent of each other
  • Example: No bias towards yR or Yr in gametes
  • Random fertilization of ovules by pollen
  • No bias of gametes for fertilization

Dihybrid Test Cross

• F1 is heterozygous for both genes (e.g., YyRr) crossed with a homozygous recessive parent (yyrr)
• Result is a 1:1:1:1 phenotypic ratio (e.g., yellow round, yellow wrinkled, green round, green wrinkled).

Patterns of Segregation

• One gene (one trait):
  • Monohybrid cross: 3:1 (F2)
  • Test cross of F1, 1:1
• Two genes (two traits):
  • Dihybrid cross: 9:3:3:1 (F2)
  • Test cross of F1, 1:1:1:1

Some Genetic Vocabulary

• Progeny: Offspring, children, results of reproduction
• Gametes: Sperm and egg; carry half the genetic information of the parent; haploid
• Zygote: Results from fusion of gametes; diploid
• Haploid: One copy of each chromosome/gene (in animals, only in gametes)
• Diploid: Two copies of each chromosome/gene (in animals, all other cells)
• Homozygous: Having two identical copies of a gene
• Heterozygous: Having two different versions of a gene
• Gene: Discrete unit of inheritance, determines protein expression
• Segments of DNA: One gene is part of a chromosome, on chromosome has many genes
• Alleles: Different forms of a specific gene
• Genotype: The alleles carried by an individual for a gene or set of genes
• Phenotype: The appearance (expression) of the alleles for a gene or set of genes
• Mutation: A heritable change in a gene, resulting in a new allele (most allele variation in genetics)
• Wild type: Standard allele, the most common allele found in the wild
• Variant allele: New allele, mutant allele

Probability

• Probability of an outcome = (# of times event is expected to happen) / (# of opportunities (trials)).
• Example: Probability of a red gum ball from a mixture of 60 red and 40 green gum balls; 60/(60+40) = 0.6

Product Rule

• Probability of independent events occurring together is the product of individual event probabilities.
• Example: Chance of getting a 5 on two dice rolls (1/6 x 1/6 = 1/36)

Sum Rule

• Probability of either of two mutually exclusive events occurring is the sum of individual probabilities.
• Example: Chance of rolling a 5 or 6 on two dice rolls

Using Both Product and Sum Rules

• Combining probability concepts for more complicated situations.
• Example: Calculating the probability of getting one green and one red gum ball when buying two from a mixture

Test your understanding of Mendelian analysis and probabilities with this quiz focused on single-gene analysis problems. Review key concepts from chapter 3 and practice your problem-solving skills. This quiz provides an opportunity to reinforce your knowledge in genetics.