Gregor Mendel's Experimental Model

Gregor Mendel's Experimental Model

• Gregor Mendel used pea plants to study how traits are inherited, choosing peas because they reproduce rapidly and have easily observable traits like flower color.

Characteristics of a Genetic Model Organism

• A model organism must have certain characteristics to be useful in genetics: • Rapid reproduction • High number of offspring • Easily observable traits • Ease of manipulation in the laboratory

Monohybridism and F1 and F2 Crosses

• Monohybridism is the study of a single trait.
• F1 (first filial generation) are the offspring of two pure-bred parents (e.g., purple peas crossed with white peas).
• F2 (second filial generation) are the offspring of the F1 generation crossed with each other.
• All F1 offspring have the dominant trait (e.g., purple flowers).
• In F2, the ratio of dominant to recessive traits is approximately 3:1.

Punnett Squares

• A Punnett square is a tool used to predict the outcome of a genetic cross.
• If one parent is homozygous dominant (PP) and the other is homozygous recessive (pp), all F1 offspring will be heterozygous (Pp) with the dominant trait.

Test Crosses

• A test cross determines the genotype of an organism with a dominant trait by crossing it with an organism that is homozygous recessive.
• If some offspring have the recessive trait, the genotype of the first parent must be heterozygous (Pp).

Law of Large Numbers

• The law of large numbers states that the larger the sample size, the closer the observed results will be to the theoretical Mendelian ratios.
• In small populations, the ratios may vary, but in large populations, the ratio of dominant to recessive traits becomes more precise.

Standard Terminology in Mendelian Genetics

• Gene: A segment of DNA responsible for a trait.
• Allele: Different versions of a gene.
• Dominant: An allele that masks the effect of another allele.
• Recessive: An allele that is masked by a dominant allele.
• Genotype: The combination of alleles an organism possesses.
• Phenotype: The observable trait or characteristic.
• Heterozygote: An organism with two different alleles.
• Homozygote: An organism with two identical alleles.

Ratios in Small Samples

• In small samples, the ratios may not correspond to the expected Mendelian ratios (3:1 for dominant:recessive).
• Small samples may produce skewed ratios, but larger samples will approach the expected ratios.

Analyzing Pedigree Trees

• A pedigree tree shows family relationships and inherited traits.
• Analyzing a pedigree tree can help deduce genotypes.
• If an individual has a recessive trait, their parents must be carriers of the recessive allele (at least heterozygous).

Consequences of Genetic Diagnostics

• Genetic diagnostics can reveal information about the risk of inherited diseases, which can have implications for health and decision-making.