Genetics Chapter Quiz

Mendel and the Gene Idea

• Gregor Mendel lived from 1822 to 1884
• Mendel studied heredity using garden peas
• Mendel studied 7 traits in pea plants, including height, flower color, seed shape
• Mendel's work disproved the "blending" hypothesis, which suggested traits were blended like mixing paint
• Mendel's work supported the "particulate" hypothesis, which indicated that parents pass along discrete heritable units (genes)

Genetics Terms

• Gamete: sex cells
• Gene: a segment of DNA that codes for a protein
• Allele: different versions of a gene
• Phenotype: the appearance of a trait (physical expression)
• Examples: Tall, yellow, round, purple, etc.
• Genotype: the allele combination which causes the phenotype
• Examples: PP, Tt, tt, etc.
• Types of genotypes
  • Homozygous (pure): PP, tt, KK, MM, qq, etc.
  • Also known as "true breed"
  • Heterozygous (hybrid): Pp, Tt, Kk, Mm, Qq, etc.

Mendel's Laws

• Mendel left teaching to study heredity.
• Chose garden peas due to easy reproduction.
• Pea plants reproduce sexually
• Male and female parts are in the same flower in pea plants
• Chose 7 traits with distinct opposite expressions for study.
• Examples: Tall vs. short, purple flowers vs. white, green seeds vs. yellow.
• Process of cross-pollination
• Mendel's work on peas is called a monohybrid cross.
  • Experiment: Cross white flower by purple flower plants

What Happened to the White Petal Trait?

• Mendel crossed two hybrid offspring together.
• Suddenly the white trait shows up again.
• This means the trait never left; just not being expressed in hybrid condition.
• Conclusion: The alleles are passed on separately! Some are dominant over others

Writing Out Mendel's Flower Color Experiment

• Law of Segregation of Unit Factors (Characters)
• Mendel called genes factors
• Each parent contributes one factor to produce the offspring
• Examples: P: PP × pp, F1: Pp (purple hybrids), F2: PP × 2 Pp × pp

Law of Dominance

• The dominant allele (gene) is expressed when paired with a recessive allele
  • Example: The dominant allele will express its phenotype (appearance).

Law of Dominance

• Law of Dominance explains how each parent contributes one factor each to produce the offspring.
  • Example: With PP × pp= Pp

Ratios and Determining Probabilities

• Ratios can be useful for simplifying raw data.
  • Example: Dividing the larger number by the smaller one
• Ratios of traits can show predictable patterns.

Probabilities Predict Averages

• Probabilities predict average outcomes of large numbers of events.
• Probabilities cannot predict the precise outcomes of individual events.
• Larger number of offspring = closer results to expected values.

Gregor Mendel's Peas

• Mendel hand-pollinated flowers (transferring pollen to carpels)
• Fertilization occurs shortly after pollination.
• The uniting of male and female gametes
• Mendel was able to produce seeds from two different parents.
• This is called cross-pollination.

The Testcross

• How can we tell the genotype of an individual with the dominant phenotype?
• Such an individual could be either homozygous dominant or heterozygous.
• Using a Testcross to figure out the genotype of an individual with a dominant phenotype. (Cross with homozygous recessive to figure out unknown)

Drawing Inferences From Data

• Data in a monohybrid cross of Rr x Rr plants
  • Raw data can be organized into a ratio by dividing the larger number by the smaller one.
  • Example: Round seeds = 882, Wrinkled seeds = 299. The ratio is 2.95:1
• Ratio can sometimes be an integer or can be rounded up or down.

Dihybrid Crosses

• Two different traits inherited together or independently. Examples: Plant height & seed shape
• Crossing two true-breeding parents differing in two characters produces dihybrids in the F₁ generation (heterozygous for both characters)
• Example: P: TTRR (tall, round) x ttrr (short, wrinkled), F1: TtRr (tall, round) , a cross between F₁ dihybrids

If Dependent Assortment...

• If two traits are dependent on one another, then a “T” might only ever be attached to a “R,” and a "t" with a "r".
• Example: Determining the predicted phenotypic ratio of this crossing.

Law of Independent Assortment

• Independent assortment of traits during dihybrid crosses helps determine the phenotypic ratios.
• Accounts for each possible combination of alleles.
• Example : TtRr x TtRr

Beyond Dominant and Recessive Alleles

• Incomplete dominance: When one allele isn't completely dominant over another, resulting in a phenotype between the two homozygous phenotypes.
• Codominance: Both alleles contribute to the phenotype, creating a mixed appearance instead of blending like with incomplete dominance.
• Example : A cross between red and white flowers could produce pink flowers (incomplete dominance).
• Multiple alleles: A gene controlled by more than two alleles.
• Polygenic traits: Traits controlled by two or more genes, show a wide range of phenotypes. Often distributed in a bell curve. Examples : hair, eye, and skin color; height

Chromosomes and Meiosis

• Chromosomes contain genes linked to each other
• Chromosomes occur in sets; one set = n
• Example : Pea plant cells have 14 chromosomes and 7 in each set
• Organisms produce gametes which contain one set of chromosomes and are said to be haploid (n)
• Cells with two sets of chromosomes are diploid (2n)
• Only gametes are haploid, all other somatic cells are diploid

Homologous Chromosomes

• Karyotype: image of a person's chromosomes arranged in numerical order
• Chromosomes occur in pairs. One from each parent (maternal & paternal sets).
• Humans have 22 pairs of autosomes and 1 pair of sex chromosomes.

Mitosis vs Meiosis

• Mitosis produces genetically identical daughter cells that match the parent cell.
• Example: 2n parent → 2 (2n daughters)
• Meiosis produces haploid cells (half the chromosome number) used in sexual reproduction.
• Sperms & Eggs

Basics of Meiosis

• Germ cells enter meiosis instead of mitosis
  • Germ cell goes through G1, S, G2 and then meiosis 1, 2

Crossing Over

• Crossing over in Prophase I of Meiosis I
• Homologous chromosomes exchange portions of their chromatids; new combination of alleles

Independent Assortment

• Independent assortment of alleles in Metaphase I & Meiosis I and II
• Independent assortment and crossing over create genetically unique gametes

Gene Maps

• Showing the relative locations of genes on a chromosome
• The farther apart genes are, the more likely they will be separated during crossing over.
• Recombination frequencies can indicate relative distances between genes.

Review Questions

• The provided document has review questions, but the questions are not specific.
• Students should refer back to the notes to answer the questions. These questions are not available in the context.