Mendelian Inheritance Quiz

Mendelian Inheritance

• Mendel, the "father of genetics", performed thousands of pea plant crosses from 1856-1864 to study inheritance patterns.
• He used the garden pea (Pisum sativum)
• His work, "Experiments on Plant Hybrids", was published in 1866 but ignored for 34 years.
• In 1900, Mendel's work was rediscovered.
• Mendel carried out self-fertilization and cross-fertilization experiments.
• Self-fertilization: Pollination and egg come from the same plant.
• Cross-fertilization: Pollination and egg come from different plants (a controlled breeding experiment)

Mendel's Study of Pea Plants

• Traits, or variants, are observable characteristics.
• A true-breeder produces the same trait over generations.
• Examples of pea plant traits include height, flower color, seed shape, and seed color.

Types of crosses

• Single factor crosses: involve two plants that differ in only one trait.
• The parental generation (P) is crossed to produce the first-generation (F1) offspring.
• The F1 plants self-fertilize to produce the second-generation (F2) offspring seeds.

Data from Single Factor Crosses

• Data on the results of various single factor crosses.

Interpreting the data

• Traits do not blend; one variant is dominant, the other recessive; this is observed in the F1 generation.
• Particulate theory of inheritance: traits are inherited as discrete units called "genes" that remain unchanged.

Law of Segregation

• Two copies of a gene separate during gamete formation.
• Each gamete carries one copy of each gene.
• "Alleles"—different forms of a gene.
• "Homozygous" = two identical alleles
• "Heterozygous" = two different alleles.
• "Genotype" = genetic makeup.
• "Phenotype" = observable traits.

Punnett Squares

• Used to predict the outcome of simple genetic crosses.
• Proposed by Reginald Punnett.
• Example of a cross between heterozygous tall plants (Tt x Tt).

Two Factor Crosses

• Involve crossing plants that differ in two traits.
• Example of traits: seed texture (round vs. wrinkled) and seed color (yellow vs. green)
• Two possible inheritance patterns:
• Linked assortment (genes close together on the same chromosome remain together during gamete formation),
• Independent assortment (genes are on separate chromosomes and segregate independently during gamete formation).

Data from Two-Factor Crosses

• Data from results of various two factor crosses, which showed patterns that were closer to expectations of independent assortment than linked assortment.

Law of Independent Assortment

• Different traits are independently inherited during gamete formation.
• Two factors assort independently during gamete formation.

Mendel's Law of Independent Assortment

• Genes are linked if they are on the same chromosome.
• Genetic recombination happens when the offspring receives a combination of alleles that differs from the parent generation due to:
• Independent assortment,
• Crossing over. Note crossing over is not in chapter 3.

Probability

• The probability an event will occur is the chance of it happening again in the future.
• Probability calculations are used to predicts results.
• Probability = Number of favorable outcomes/Total number of possible outcomes

Chi Square Test

• A statistical method to determine if there is a good fit between the data and hypothesis.

P Value

• The P-value is an important tool in statistics that measures the probability of observing results as extreme as, or more extreme than, the observed results, assuming the null hypothesis is true. A lower P-value suggests stronger evidence against the null hypothesis (supporting your desired outcome).

Modern Genetics

• Defective copies of genes are called 'loss-of-function alleles'.
• Loss-of-function alleles are commonly inherited recessively (the gene must be present on both allele copies.)

The Chromosome Theory of Inheritance

• Chromosomes carry the genetic material.
• Chromosomes are replicated and transmitted to offspring.
• Eukaryotic cell nuclei contain chromosomes in homologous pairs.
• During meiosis, homologs and different chromosome types segregate independently.
• Each parent provides one chromosome set to the offspring.

Pedigree Analysis

• Used to determine patterns of inheritance of traits in humans.
• Pedigrees demonstrate a family's inheritance of a genetic trait over generations.
• This can determine if a trait or disease is dominant or recessive.
• Genes that are related to diseases can exist as non-disease-causing alleles or as disease-causing mutant alleles.

Additional Information

• Concepts of product rule and binominal expansion are useful for probability calculations in genetics problems, especially when the genetic trait is expressed over multiple factors (multiple genes).
• Calculating the probability of a specific outcome (e.g. congenital analgesia in offspring).