!! GENETICS!! --- Part 4

Monohybrid:

• A monohybrid cross is a mating between individuals who have different alleles at one genetic trait of interest. The character(s) being studied in a monohybrid cross are governed by two alleles for a single trait.
• To carry out such a cross, each parent is chosen to be homozygous or true breeding for a given trait. When a cross satisfies the conditions for a monohybrid cross, it is usually detected by a characteristic distribution of second-generation (F2) offspring that is sometimes called the monohybrid ratio.
• Monohybrid cross - a cross between parents that differ at a single gene pair (usually AA x aa)
• Monohybrid - the offspring of two parents that are homozygous for alternate alleles of a gene pair Remember!! --- a monohybrid cross is not the cross of two monohybrids.
• Generally, the monohybrid cross is used to determine the F2 generation from a pair of homozygous grandparents (one grandparent dominant, the other recessive), which results in an F1 generation that are all heterozygous. Crossing two heterozygous parents from the F1 generation results in an F2 generation that produces a 75% chance for the appearance of the dominant phenotype, of which two-thirds are heterozygous, and a 25% chance for the appearance of the recessive phenotype. 

  

* In the figure above, inheritance pattern of dominant (red) and recessive (white) phenotypes when each parent (1) is homozygous for either the dominant or recessive trait. All members of the F1 generation are heterozygous and share the same dominant phenotype (2), while the F2 generation exhibits a 3:1 ratio of dominant to recessive phenotypes (3).

Dihybrid:
A dihybrid cross is a cross between F1 offspring of two individuals that differ in two traits of particular interest. A dihybrid cross is often used to test for dominant and recessive genes in two separate characteristics.

*Two genes that are heterozygous mix together. When two genes that are heterozygous cross over, the phenotypical ratio is 9:3:1.