Question bank: Basic Genetics

The first law of Mendel, also known as the Law of Segregation of Factors, was formulated by the physician and biologist Gregor Johann Mendel based on experiments conducted with peas. The law states that the inherited traits from parents are transmitted to offspring independently. What are the two main components of this law?

Pedigrees are useful in identifying genetic diseases that can be passed from parents to children. For example, albinism is a genetic disease caused by mutations in the melanin gene, responsible for skin, hair, and eye pigmentation. Albinism is characterized by which symptoms?

In a plant species, flower color is determined by a pair of alleles, R and r, with R producing red pigment and r resulting in the absence of pigment, leading to white flowers. In a cross between two plants heterozygous for this trait (Rr), what is the probability of obtaining a plant with a red flower that is homozygous for the R allele? Explain the reasoning behind the calculation, considering Mendel's laws and the independent assortment of alleles.

In his experiments, Mendel crossed pea plants with yellow seeds and others with green seeds, always obtaining a 3:1 ratio between plants with yellow seeds and those with green seeds in the subsequent generations. This result was explained by the Law of Segregation, which states:

In a plant species, the color of the flowers can be white, red, or pink. Two heterozygous individuals (Bb) are crossed. According to Mendel's laws, 25% of the offspring should exhibit the white phenotype, but field observations reveal that only 10% of the descendants have white flowers. Considering that Mendelian genetics predicts the inheritance of traits in exact proportions and that flower color in plants follows a pattern of simple genetic inheritance, explain why the field observation differs from Mendelian expectations and discuss possible explanations for this phenomenon. Provide the calculation of the expected probability, considering Mendelian proportions, and explain how a deviation from these proportions may result from other genetic mechanisms, such as mutations or natural selection.