The Genetics of Inheritance

The Genetics of Inheritance

Early theories of inheritance included the ‘blending theory’ which suggested that the egg and sperm mixed together resulting in offspring that were a bland of the parent’s characteristics

Eg. Offspring of a plant with red flowers and a plant with white flowers would be a plant with pink flowers

However, this was not always the case, so the theory was not a strong one

The explanation of how some distinguishing characteristics (traits) are inherited came from the Austrian monk Gregor Mendel in the 1850’s

Mendel proposed a “particulate” mechanism for inheritance. He felt that parents pass on discrete heritable units (which we now call genes) to their offspring

Mendel and Experiments

- studied the common pea plant over 8 years

Peas were excellent organisms for Mendel to choose:

(1) easy to grow

(2) mature quickly

(3) sexual organs of the plan are entirely enclosed; easy to manipulate

(4) easily observable traits each trait had 2 possible variations

Traits in pea plants studied by Mendel:

(1) seed shape (round/wrinkled)

(2) seed colour (yellow/green)

(3) flower colour (purple/white)

(4) flower position (axial/terminal)

(5) pod colour (yellow/green)

(6) pod shape (inflated/constricted)

(7) plant type (tell/dwarf)

Mendel chose to study plants which, over many generations of self-pollination, produced only the same variety as the parent plant, this there’s were true breeding or pure bred for the trait he was studying

Mendel’s Laws of Inheritance:

(1) Law of segregation

- alternative versions of genes account for variations in inherited characteristics. Eg. – for flower colour in pea plants there are 2 versions of the gene – one for purple flowers, one for white flowers

- for each trait, an organism inherits 2 copies of the gene – one from each parent. These copies are called alleles

- pone allele is dominant and determines the organism’s appearance and the...