A level GENETICS PART 1 of 7

The notes presented below can be used by both Ordinary and Advanced Level students

INTRODUCTION TO GENETICS

The very idea of how people look alike but different is actually amazing. A human always gives birth to a human but NO two humans are the same. Not even identical twins? Homogenous twins result from the fact that an egg is fertilized by one sperm but successfully divides mitotically before a week. If one egg and one sperm fuse, then the genome should be integrally the same, so is there any true genetic difference? Well, genetics studies and answers all these questions.

Genetics is the study of heredity and variation. The former refers to inheritance from parents while the latter refers to the changes observed during the process of heredity.

How did genetics start?

Gregor Mendel

Gregor Mendel (Above).

Gregor Mendel is often given the credit of founder of Genetics as he presented the first and probably the most outstanding breakthrough of genetics when he published his paper on inherited traits in pea plants. Gregor Mendel was an Austrian Priest but was equally a Mathematician, Meteorologist and biologist. In the Catholic, two hectare garden where he served, he decided to study hereditary in pea plants. After studying heredity and variation in pea plants for seven (7) years, he published the article in the year 1865. Gregor Mendel’s choice of organism as test subject was not arbitrary but was influenced by a set of factors that are somewhat obvious but intriguing.

Why did Gregor Mendel choose pea plants for his experiments?

They are Generational organisms. This implies that pea plants reproduce at a given period of the year. This gave Mendel the possibility to accurately get large samples for his experiments. Not only will he collect the large samples but he will have enough time to count and analyse them. Let’s assume a situation where the organism reproduce at any time like the human being. If he harvest in January, by the time he finishes to analyse the results, there might have already been cross breeding and the experiment gets messed up. Seeing therefore that the plants are generational, that is, they all produce seeds at the same time of the year and spring fort flowers in the same period, etc. He can hence, collect his data and while the plants are in their growth phase, he can then perform his analysis.

They have a variety of observable traits. Pea plants present a large variety of phenotypically expressed genes. They have grains of different sizes and lengths, smooth or hairy, length of pods, colour of flowers etc. All these characteristics made Mendel’s work simpler as they were readily observable. As a matter of fact there are exactly seven characteristics that Mendel Studied on the Pea plants.

Their flowers are bisexual. If a single flower has both Androecium (the male reproductive ‘section’ of a flower) and Gynoecium (the female reproductive ‘section’ of a flower), then the plant has the possibilities for both self and cross fertilization. Self-pollination will ensure a cross with parental genes and a lot of other possible analysis.

So, for the reasons stated above, Mendel found pea plants to be best for all his experiments. He most evidently used their hermaphroditic (a single organism with both genders/sexes) nature to cross breed organisms of opposing phenotypes just to see the outcome. This equally favoured test crossing.

Mendel’s less than a decade work ended up as the foundation for modern day genetics. Hence, he is referred to as the father of genetics. Nonetheless, there exist exceptions to his work. This divides genetics into two: Mendelian genetics and non-mendelian genetics. (Check out Part three and four.)

The study of genetics is involved with a lot of terminology. The discipline has its own language or vocabulary. Hence, before we sink deep into the study of genetics, we must get to know basic definitions in order to facilitate the understanding process. Nonetheless, that will be done as part two of the notes under genetics part two.