Episode 146: Mendelian Genetics and Inheritance

Mendel's Work

Gregor Mendel's experiments with pea plants were groundbreaking in the field of genetics. James Fodor explains how Mendel crossed green and yellow pea plants, observing that the first generation (F1) all had the same phenotype, which was green. However, in the second generation (F2), the yellow phenotype reappeared, leading to the discovery of the law of dominance and the 3:1 ratio of phenotypes 1.

Mendel postulated the law of dominance, which was to say that if two alleles differ, so if you've got a green and a yellow one will dominate the other and have its phenotype fully expressed.

--- James Fodor

This experiment laid the foundation for understanding how traits are inherited from one generation to the next 2.

   

Segregation

The law of segregation is a key principle in Mendelian genetics. James Fodor describes how each organism inherits two factors (now known as alleles) for each trait, one from each parent. These alleles segregate independently during the formation of gametes, leading to the random assortment of traits in offspring 3.

The law of segregation, the random distribution of the factors from parents to children, occurs because of the random distribution of chromosomes during meiosis.

--- James Fodor

This principle explains the genetic variation observed in offspring and is fundamental to the study of genetics 4.

   

Inheritance Ratios

Mendel's experiments revealed specific inheritance ratios, such as the 3:1 ratio in the F2 generation. James Fodor explains that this ratio results from the dominance of one allele over another and the independent segregation of alleles 1. He also discusses how real-world genetics often involve more complex interactions, such as incomplete dominance and epistasis.

In reality, most traits have variable penetrance and variable expressivity. And typically this is because of gene interaction effects and also interactions of genes in the environment.

--- James Fodor

These insights help us understand the complexities of genetic inheritance beyond simple Mendelian ratios 5.