Sex Linkage and Epistasis

This page delves into more advanced genetic concepts, focusing on sex linkage and epistasis explained with punnet squares. It begins with an explanation of sex-linked inheritance, using color blindness as an example.

Example: In a cross between a carrier female (XᴿXʳ) and a healthy male (XᴿY), there is a 25% chance of having a color-blind male offspring.

The page illustrates different scenarios of sex-linked inheritance, including a color-blind male crossed with a healthy female, demonstrating how the trait is passed differently to male and female offspring.

Highlight: In a cross between a color-blind male and a healthy female, all female offspring will be carriers, while all male offspring will be healthy.

The concept of epistasis is then introduced, using coat color in horses as an example. This demonstrates how one gene can mask or modify the expression of another gene.

Definition: Epistasis occurs when the expression of one gene is affected by the presence or absence of one or more other genes.

A detailed punnet square is provided to show the inheritance of two interacting genes: one controlling pigment production (B for black, b for brown) and another controlling an enzyme that degrades pigment (E for enzyme present, e for enzyme absent).

Example: A horse with the genotype BBEE will be white, despite having the genes for black coat color, because the E gene produces an enzyme that degrades all pigment.

The page concludes with a complex punnet square demonstrating the F2 generation of this epistatic interaction, showing the various possible genotypes and their corresponding phenotypes.

Vocabulary: Autosomal linkage refers to the inheritance of genes located on non-sex chromosomes, which can lead to more complex inheritance patterns than those seen with single-gene traits.

This comprehensive guide provides a thorough understanding of advanced genetic concepts, using clear examples and punnet squares to illustrate complex inheritance patterns.

Monohybrid and Dihybrid Inheritance

This page covers the basics of understanding punnet squares for monohybrid and dihybrid inheritance. It starts with a monohybrid cross example for eye color, showing how to determine offspring genotypes and phenotypes. The dihybrid cross example demonstrates inheritance of two traits - flower color and shape.

Vocabulary: Monohybrid inheritance refers to the inheritance of a single gene, while dihybrid inheritance involves two different genes controlling separate characteristics.

Example: For eye color, B represents brown eyes (dominant) and b represents blue eyes (recessive). A cross between two heterozygous parents (Bb x Bb) results in offspring with a 3:1 phenotypic ratio of brown to blue eyes.

The page also introduces co-dominance in genetics with punnet square examples. This is illustrated using flower color, where red and white alleles are co-dominant, producing pink flowers in heterozygous plants.

Definition: Co-dominance occurs when two alleles are equally dominant and both are expressed in the heterozygous condition.

Blood type inheritance is used as a real-world example of co-dominance. The ABO blood group system is explained, showing how different allele combinations result in the four main blood types (A, B, AB, and O).

Highlight: In a cross between parents with AB and O blood types, there is a 50% chance of offspring having blood type A and a 50% chance of blood type B.

The page concludes with a detailed dihybrid cross example involving flower color (yellow vs. white) and stem length (long vs. short). This demonstrates how to use larger punnet squares to predict offspring ratios for two independently inherited traits.