Gregor Mendel

Who is he

Austrian Monk who is known as the father of genetics. Developed the laws of inheritance when cultivating and testing pea plants and their inheritance of traits.

Why pea plants

They can be grown in large quantities so they can be cultivated in large numbers. They produce large numbers of offspring (seeds). They had short life cycles meaning multiple generations could be studied in a short time. Many have female and male reproductive organs

How can pea plants self-pollinate

It has both reproductive organs, so the stamen (male) part can be cut off before they release pollen and the pollen can be transferred using a brush to another plant to fertilise, cross breed and produce future generations.

What does true breeding mean

When organisms self fertilise with another of the same type to produce offspring with the same trait consistently.

What was Mendels experimental plan

Select varieties of peas that could be studied for their heritable characteristics and traits. Used true breeding so the heritable trait would be the only form present for many generations.

Monohybrid cross

Cross involving a single trait. In the first generation, the dominant allele will be possessed. In the second generation, a 3:1 ratio will be observed.

Dihybrid cross

When two characteristics are studied and is determined by 2 different genes that are present on 2 different chromosomes at the same time.

Mendels first experiment

He studied different traits of a single character. He crossed true breeding round seed with true breeding wrinkled seeds. In F1, all the offspring had round seeds and the wrinkled trait failed to appear.

What did Mendels first experiment lead to

It led to the law of dominance. Some alleles are dominant so they will express their trait even if only one copy is present. While other alleles are recessive, they require 2 copies.

Particulate theory

Traits are passed down in discrete units (genes) that remain intact across generations.

Law of segregation

Each organism carries 2 alleles for a trait. One from each parent. these alleles segregate during the formation of gametes. Each gamete receives one allele. Fertilisation occurs and offspring inherit one copy from each parent restoring the two-copy state. This is why recessive traits appear in the second generation after being hidden in the first.

Law of independent assortment

Traits are inherited independently of one another. The inheritance of one trait doesn’t influence the inheritance of another.

Mendels experiment of the dihybrid cross

He studied two traits at the same time (seed shape and colour). He crossed plants that were round + yellow with plants that were wrinkled + green. The F1 only had round and yellow seeds. F2 generation produced seeds in a 9:3:3:1 ratio showing that traits were inherited independently.

Incomplete dominance

Heterozygous offspring show a blended phenotype rather than expressed only the dominant trait. The original allele remains intact and can still be passed to the next generation.

Codominance

Both alleles are fully expressed in the heterozygous individual without blending. Allows both traits to appear distinctively.

Blood types and codominance

A person inherits type A and type B blood from each parent. So the genotype is AB. Both alleles produce different antigens on red blood cells, neither is dominant over the other. Both antigens appear on the surface making the blood type AB.