Bio 1000- Genetics: Intro

MENDEL & THE BEGINNING TO GENETICS

For the longest time, scientists believed in the blending theory of inheritance, which suggests that hereditary traits blend evenly in offspring through mixing of parent's blood. However, this blending did not explain the appearance and disappearance of extremes like height and colour of the eye.

NOW HERE COMES MENDEL
Gregor Mendel, the father of genetics used garden peas to bring the notion of genetics to the scientific world. In his work with peas, Mendel studied variety of heritable characteristics called characters( flower colour or seed shape). Variation in character is what is referred to as trait (purple or white flower).
Mendel established that characters are passed to offspring in the form of discrete hereditary factors which are known as genes. He observed that rather than blending evenly, many parental traits appear unchanged in offspring, whereas others disappear in one generation to reappear in the next generation.

MENDEL CHOSE TRUE-BREEDING GARDEN

Mendel chose the garden pea for the following reasons:

1. Easy to grow
2. Ability to self-fertilize or self-pollinate
• Sperm nuclei in polled produced by anthers fertilize egg cells housed in the carpel of the same flower

Mendel, however cut the anthers to prevent self-fertilization which meant that pollen must come from another flower. This is referred to as cross-pollination which allowed Mendel to test effects of mating pea plants of different parental types.

He began his experiments with pea plants that are known as true-breeding which means when self-fertilized, they pass on their traits unchanged from one generation to the next.

NOW HE DECIDES TO CROSS-BREED- WHAT HAPPENS?

To really understand cross breeding and this blending idea, he wondered if traits blend evenly if plants with purple flowers cross pollinated with white flowers.
To do this:

He took the pollen from purple flower and added it to stigma of the white flower and vice versa

Result:

Seeds were the result of the crosses, which each contained a zygote or embryo that would develop into a pea plant.

Plants that develop from the seeds produced by the cross-the first generation of offspring from cross= F1 generation
Plants used in initial cross are called parental or P generation

Now back to his initial testing, the result when purple flower was cross-pollinated with white:

• All F1 seeds formed purple flowers and white flower trait completely disappeared.

To test again, he took the F1 plants and allowed it to self-fertilize to produce seeds that represented F2 generation. The result:

• Both white and purple flowers reappeared