Mendelian Genetics Chapter Notes

Date: 4/17
Honors posters are due tomorrow by 4pm.
Poster session scheduled for 4/25 from 2-4pm, attendance required for honors students.
Watch for biocoach review sessions next week.
Office hours today from 1-3pm.

Gregor Mendel conducted experiments on peas in the 1840s to establish rules of inheritance.
The Chromosomal Theory of Inheritance (1902-1903) links genetic information transmission to meiosis.
Mendel asserted that genes are located on chromosomes.

Mendel's interest arose from selective breeding questions concerning trait transmission patterns from parents to offspring.
Two main hypotheses at the time:
1. Blending inheritance: Traits from parents blend in offspring.
2. Inheritance of acquired characteristics: Traits are modified through use and passed down.

First model organism in genetics: Garden pea.
- Polymorphic traits: Traits appear in now, with observable features (phenotypes) drawn from these traits.
- Conclusions applicable to other species.

Gene: Hereditary factor influencing a trait.
Allele: Specific form of a gene.
Genotype: Combination of alleles in an individual.
Phenotype: Observable traits of an individual.
Homozygous: Two identical alleles.
Heterozygous: Two different alleles.
Dominant allele: Expressed in both homozygous and heterozygous forms.
Recessive allele: Only expressed in homozygous form.
Testcross: Cross of an individual with an unknown genotype with a homozygous recessive individual to determine genotype.

Example: Round vs. wrinkled seeds.
- 3:1 ratio of dominant to recessive traits in F2 generation.
- Gender has no influence (reciprocal crosses).

Proposed Particulate Inheritance: Heritable traits do not blend but behave as discrete units.

Principle of Segregation: Each gene pair segregates during gamete formation (anaphase I).
Principle of Independent Assortment: Genes on different chromosomes assort independently (metaphase I).

Gene Linkage: Genes on the same chromosome tend to be inherited together unless crossing over occurs.
Multiple allelism: More than two allele forms exist for a gene (e.g., ABO blood types).
Codominance: Both alleles manifest in the phenotype (e.g., roan cattle).
Pleiotropy: One gene affects multiple traits (e.g., Marfan syndrome).

Gene-gene interaction: Expression of one gene depends on the presence of another.
Gene-environment interaction: Traits influenced by environmental factors alongside genetics (e.g., PKU).
Quantitative traits: Traits influenced by multiple genes resulting in continuous variation (e.g., height).

Pedigree analysis is essential in determining whether an inherited trait is dominant or recessive, as well as determining its linkage to sex chromosomes.
Examples: Autosomal recessive traits (e.g., sickle-cell disease) and Autosomal dominant traits (e.g., Huntington's disease).

Study Mendel's principles, how they apply to both plant and human genetics, and exceptions to Mendelian inheritance such as gene linkage and multiple allelism. Prepare for application through pedigree analysis of various traits in human populations.