Bio 1000- Genetics : Mendel's Perspective

MENDEL'S THREE HYPOTHESES

Mendel developed the first hypothesis through his observation as :

"Adult plants carry a pair of factors that govern the inheritance of each character"

That is, for each character, an organism inherits one factor from each parent. In this case, factor refers to the genes located on the chromosome. Alleles are different version of a gene that produces different traits of character. Organisms with two copies of each gene is referred to as diploids. Note that the 2 alleles of a gene in a diploid individual can be identical or different.

Mendel developed his second hypothesis as:

"If an individual's pair of gene consists of different alleles, one allele is dominant over the other, the recessive allele"

WHAT MAKES AN ALLELE DOMINANT?
When an organism carries 2 different alleles, the dominant allele is simply the one that determines the appearance of the organism.

Mendel proposed his final hypothesis as:

"The pairs of alleles that control a character segregate/ separate as gametes are formed. Half the gametes carry one allele and the other half carries the other allele."

This referred to as PRINCIPLE OF SEGREGATION.

During fertilization, fusion of the haploid maternal and paternal gametes produces a diploid nucleus called zygote nucleus. Zygote nucleus receives one allele for the same character from the female gamete, reuniting the pairs.
POSSIBLE COMBINATIONS:

1. An individual with combination of the same alleles is called homozygote and is said to be homozygous for the particular trait
2. An individual with combination of different alleles is called heterozygote and is said to heterozygous for the particular trait

A F1 heterozygote produced from a cross that involves a single character is called monohybrid (PP x pp=Pp)
Generally, a cross between 2 individuals that are heterozygous for the same pair of alleles is called monohybrid cross (Pp x Pp)

MODERN TERMINOLOGY:
Genotype: Genetic constitution of an organism
Phenotype: Outward appearance