Outline the experiments carried out by Gregor Mendel

1. Outline the experiments carried out by Gregor Mendel

2. Introduction • Gregor Mendel (1860s), an Austrian Monk, formulated the principles of genetics by careful and methodical experimentation with garden peas.

3. Introduction • He wrote that ‘factors’ (genes) were passed on from parent to child that could produce the same physical characteristics. • It wasn’t until the 1900’s that Mendel’s findings were formally recognised.

4. Mendel and Genetics • The appearance of an organism is the result of two factors: 1. the gene being expressed 2. the environment • Mendel stated that each individual has two factors for each trait, one from each parent. • The two factors may or may not contain the same information. • The alternative forms of a factor are called alleles.

5. Homozygous and Heterozygous traits • If the two factors are identical the individual is called homozygous for the trait (pure bred) • If the two factors have different information, the individual is called heterozygous. (hybrid) • In heterozygous individuals the only allele that in expressed is the dominant. • The recessive allele is present but its expression is hidden.

6. Mendel’s experiment • Mendel chose garden peas as he was also able to strictly control the breeding patterns of his peas for the following reasons; • They were easy to grow, • produced new generations quickly, and • had easily distinguishable characteristics.

7. What did Mendel look at? Mendel examined the following seven characteristics found in peas: • Flower colour (purple or white) • Flower position (axial or terminal) • Seed colour (yellow or green) • Seed shape (round or wrinkled) • Pod shape (inflated or constricted) • Pod colour (green or yellow) • Stem height (tall or short)

9. Why was Mendel successful?Accuracy, reliability, validity… • He cross-fertilised plants by hand with a small brush • He prevented pollination by other plants by covering the flowers with small sacks • He crossed pure breeding parents with easily identifiable characteristics • Each characteristic studied was determined by 1 pair of genes • Genes for each characteristic are found on separate chromosomes • He did multiple crosses and repeated it thousands of times (large sample sizes and repetition)

11. Why was Mendel successful? • Mendel ensured pure bred plants by allowing them to self-fertilise over many generations while removing any plant with a contrasting characteristic. • He eventually got a different set of pure-breeding plants with each of his seven characteristics.

12. Why was Mendel successful? • Once Mendel was sure he had 2 populations of plants with contrasting features (e.g. Purple flowers and white flowers), he cross bred them and grew the seeds that resulted. This was called the first generation (or F1). • He noticed that this produces all purple flowers

13. Why was Mendel successful? • He then self fertilised these purple flowered plants (F1 x F1) and grew these offspring (F2). Instead of all purple, this produced 75% purple and 25% white flowered plants (3:1 ratio). • He noticed this ratio for each of the seven characteristics he studied.

14. Dominant and recessive factors • Each of the seven traits that Mendel studied had a dominant and a recessive factor. • When two true-breeding plants were crossed, only the dominant factor appeared in the first generation of offspring. • The recessive factor appeared in the second generation in a 3:1 (dominant : recessive) relationship.

15. Lets do some Monohybrid crosses (punnett squares) to show this…