Genetics Chapter 3 Quiz

Teaching Assistant Office Hours

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

Mendelian Analysis & Probabilities

• Topics Covered:
  • Mendel's peas and crosses
  • Law of Segregation
  • Law of Independent Assortment
  • Product rule
  • Sum rule

Practice Problems

• Chapter 3:
  • Single-gene analysis problems range from 14 to 43 (4th edition) & 14 to 43 (5th-7th edition)
  • Two-gene analysis problems from 15 to 40 (4th edition) & 16 to 43 (5th-7th edition).
• Problems will NOT be graded.
• Separate problem set for grading (approximately 10 problems) will be assigned later, covering material from multiple lectures.

Test Crosses

• Used to determine the genotype of a phenotypically dominant individual
• Cross with a phenotypically recessive individual.
• Test for hidden recessive genes using a homozygous recessive tester strain.
• The phenotype of the progeny from the test cross indicates the genotype of the tested parent.
• A test cross allows determination of alleles carried by the F1 parent. The recessive allele from the tester parent and the phenotype of the resulting progeny determine the genotype of the F1 parent.

Expected Results of a Test Cross

• Yellow peas are dominant over green peas.
• If yellow pea is heterozygous (Yy):
  • Expect 50% Yy progeny(yellow)
  • Expect 50% yy progeny (green)
• If yellow pea if homozygous (YY):
  • Expect 100% Y- progeny (yellow)
  • Expect 0% yy progeny (green)

Mendel Followed Two Genes at Once

• Traits for consideration: pea color and shape.
  • Y (yellow), y (green)
  • R (round), r (wrinkled)
• Problem: A true breeding plant with round, green seeds is crossed with a true breeding plant with wrinkled, yellow seeds; find the genotypes and phenotypes of the parental and F1 generations.

Tracking Two Genes

• Pure-brreeding parentals
• F1 are all RrYy (round, yellow).
• Self-fertilize F1
• Observe 9:3:3:1 ratio.
• The phenotypes did not stay together in the offspring.

Dihybrid Cross

• In a "dihybrid" cross, parents are heterozygous for two traits.
• Each dihybrid plant produces four gamete types equally frequently. Example: YyRr creates YR, Yr, yR, yr gametes.

Punnett Square for a Dihybrid Cross

• Each F1 produces four different types of gametes in equal proportions.
• These gametes come together randomly to form a zygote..
• Conclusions: Each single trait still gives 3:1 ratio, overall ratio is 9:3:3:1

Mendel's Second Law (Law of Independent Assortment)

• Segregation of alleles of two different genes is independent of one another.
• Example of this law is no bias toward (yR or Yr) (gametes)
• Random fertilization of ovules by pollen, no bias of gametes for fertilization.

Dihybrid Test Cross

• F1 heterozygous for both genes (YyRr).
• Cross F1 (YyRr) with yyrr
• Ratio of phenotypes from this test cross is 1:1:1:1

Patterns of Segregation

• One gene (one trait, two phenotypes):
  • Monohybrid cross - 3:1 (F2) phenotypic ratio.
  • Test cross of F1 - 1:1 phenotypic ratio.
• Two genes (two traits, four total phenotypes):
  • Dihybrid cross - 9:3:3:1 (F2) phenotypic ratio.
  • Test cross of F1 – 1:1:1:1 phenotypic ratio.

Some Genetic Vocabulary

• Progeny – offspring, children, results of reproduction
• Gametes – sperm and egg; carry half the genetic info of parent; haploid
• Zygote – results from fusion of gametes; diploid
• Haploid – one copy of each chromosome/gene
• 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 the expression of proteins, segments of DNA on a chromosome
• Alleles – different forms of a specific gene
• Genotype – the alleles carried by an individual
• Phenotype – the appearance (expression) of alleles
• Mutation – heritable change in a gene (new allele)
• Wild type – standard allele, most common allele in the wild
• Variant allele = new allele = mutant allele

Probability

• Probability of an outcome = (# of times event is expected to happen) / (# of opportunities (trials))
• Sum of all probabilities of all possible events = 1

Product Rule

• The probability of independent events happening together is the product of their individual probabilities

Sum Rule

• The probability of either of two mutually exclusive events occurring is the sum of their individual probabilities

Using both Product and Sum Rules

• Example using a gumball machine: calculating probability of getting one green and one red gumball in a row.

Test your understanding of Mendelian genetics with this quiz focusing on the principles of inheritance and probabilities. Topics include Mendel's laws, single-gene, and two-gene analysis problems. Perfect for those attending study hours with TAs for extra tips and insights.