Introduction to Genetics Today we know that DNA

Introduction to Genetics

Today we know that DNA exists, and we know what it does. But, the ideas of genetics and heredity came well before we knew about DNA. Genetics is the branch of biology that studies heredity. § Heredity is the passing of traits, or characters, from parents to offspring. •

Gregor Mendel: The Father of Genetics Gregor Mendel was an Austrian monk born in 1822. His parents were peasants with a background in agriculture. Mendel was an expert botanist. Called “The Father of Genetics” because he was one of the first to study patterns of inheritance.

Mendel’s Studies q. Mendel used pea plants to perform his studies q. He kept detailed records of his pea plants among many generations q. Using statistics, he was able to predict the outcome of his experiments q. New and exciting theories were established!

Why are peas so good for studying genetics? There are 3 main reasons: 1. The male and female parts of the pea plant are enclosed inside the same flower, so it is easy to control mating. 2. The peas are easy to grow, and they grow fast. They also produce lots of offspring. 3. Each character of garden peas comes in 2 clearly different forms. For example, they either have purple or white flowers, or their stems are either long or short.

Mendel kept close record of 7 different characters of pea plants: 1. flower color 2. seed shape 3. flower position 4. pod shape 5. seed color 6. pod color 7. stem length

Mendel and monohybrid crosses Mendel's experiments involved many monohybrid crosses. -Mono = one -Hybrid= a cross of different traits A monohybrid cross is used to examine the distribution of one set of genes among two organisms.

Determining the Traits of an organism: True breeding via self fertilization During Mendel's studies, it was important that he let some of the pea plants self-fertilize.

Why is self fertilization important in Mendel’s studies? In Mendel’s studies, self-fertilization was performed to ensure its offspring will have the same characteristics as the original parent. If the offspring are not all identical, then the original parent is not a true-bred. If all offspring are identical, then the original parent is truebred. The true-bred plants serve as the P, or parental, generation of Mendel's studies.

Steps of Mendel’s Experiments The P generation consists of the first two true-bred individuals that are crossed. The P stands for Parental. The offspring of the P generation is called the F 1 generation. F stands for filial, which means “son” or “daughter”. The second step in Mendel's experiments was to allow the F 1 generation to selffertilize, which creates the F 2 generation, or the second filial generation.

Mendel's Results Upon reviewing the F 2 generations multiple times, it was clear that a pattern existed.

In the F 1 generation all white flowers had disappeared, but in the F 2 generation, some had come back! The ratio seen in the F 2 generation was 3: 1, 3 purple flowers for each white flower. Purple is dominant over white, how could the white flower reappear?

Gregor Mendel came up with two laws that he discovered during his experiments: 1. Mendel’s Principle of Dominance: states that some alleles are dominant and others are recessive. Individuals with at least one dominant allele will exhibit the dominant trait. 2. Mendel’s Law of Segregation: states that the members of each pair of alleles separate when gametes are formed. A gamete will receive one allele or the other, but not both.