Genetics and Mendel's Laws of Inheritance

Mendel’s experiments and breeding strategies
Definition of Mendel’s 1st law (segregation) and 3rd law (dominance)
Mitosis vs. meiosis: similarities and differences
Distinction between gene and allele
Yeast as a model organism: haploid and diploid life cycles
Drosophila (fruit fly) as a model organism for gene mapping
Sex-linked inheritance and its role in establishing the chromosomal basis of heredity
Inheritance probability deduction using pedigree data

Focus on 7 traits in pea plants:
- Seed shape: Round or wrinkled
- Seed color: Yellow or green
- Flower position: Axial or terminal
- Flower color: Purple or white
- Pod shape: Inflated or pinched
- Pod color: Green or yellow unripe
- Stem length: Long or short
True breeding: Plants that, when self-fertilized, produce offspring with the same phenotype.
Goals: Understanding inheritance through controlled crosses.

Cross-Pollination:
- Hybridizes one plant with another
- Process: Transfers pollen with a brush after removing anthers from one plant
Selfing (Self-Pollination):
- Plant transfers pollen to its stigma
- Results in progeny identical to the parent.

Monohybrid cross outcomes:
- 3:1 phenotypic ratio in F2 generation when one trait is dominant.
Homozygous vs. Heterozygous:
- Homozygous (e.g., YY or yy) vs. Heterozygous (e.g., Yy)
Equal segregation of alleles into gametes during meiosis.

Law of Segregation:
- Each individual has two alleles for a trait that segregate during gamete formation.
Law of Dominance:
- In a heterozygote, the dominant allele expresses its effect, while the recessive allele is masked.

Mitosis:
- Produces 2 diploid daughter cells (2n)
- Functions in growth and tissue repair.
Meiosis:
- Produces 4 haploid daughter cells (n)
- Essential for gamete formation
- Involves two rounds of cell division (Meiosis I and II).

Saccharomyces cerevisiae:
- Can exist as haploid or diploid,
- 2 mating types (a and α).
Reproduction: can reproduce asexually via mitosis or sexually through meiosis,
- Forming four haploid spores (meiocytes) under specific conditions.

Key organism for genetic studies due to:
- Rapid life cycle
- Easily observable mutations (e.g., eye color)
Thomas Hunt Morgan:
- Used Drosophila to demonstrate inheritance patterns and linkage, especially in sex-linked traits.

Human sex chromosomes (X/Y):
- Traits linked to X are often recessive and affect males more frequently.
- Nettie Stevens discovered XY sex determination and its link between chromosomes and traits.

Autosomal Recessive:
- Can skip generations; affected offspring often born to unaffected parents.
Autosomal Dominant:
- Does not skip generations; approximately half the offspring of affected individuals will be affected.
X-Linked Recessive:
- Typically affects males; affected fathers do not pass the trait to sons.
X-Linked Dominant:
- Affected fathers pass the trait to all daughters but no sons.

Product Rule: Probability of two independent events occurring together is the product of their individual probabilities.
Sum Rule: Probability of occurrence of one event or another (mutually exclusive events) is the sum of their individual probabilities.

Inheritance patterns can be straightforward (single gene) or complex (multiple genes).
Many human diseases are caused by single-gene mutations (e.g., Phenylketonuria, Hemophilia).
Genetic analysis continues to rely on foundational principles established by Mendel, applicable to modern biogenetics and pedigree analysis.