1. Introduction to Genetics
Mendel
Introduction to Genetics

2. Inquiry Activity 1. Are traits inherited? 2. If so, from whom?
3. What are some examples of inherited traits that you see in yourself or in classmates?
4. Human Inheritance Lab…

3. What are we going to learn?

4. Gregor Mendel
An Austrian monk who was important in our understanding of biological inheritance. (1822)
Genetics – scientific study of heredity
Studied pea plants
Terms you should know:
Character – a heritable feature (eye color)
Trait – a variety of a character (brown eyes)

5. Pea plant basics… Flowers are used for reproduction
Male part (stamen) produces pollen
Female part (carpel) produces eggs
Normally self-pollinate
Fertilize themselves
True-breeding: if allowed to self-pollinate, they would have offspring identical to themselves  a tall plant would produce tall plants

6. Mendel’s Experiments Peas can cross-pollinate.
Mendel prevented self-pollination by removing the male parts of a flower, then he dusted the flower with pollen from another plant.
Produced crosses of the two plants
Crosses between parents with different traits are called “hybrids”

7. Mendel’s Experiments
Each character Mendel studied had 2 possible traits
He called the original pair of plants the P (“parental”) generation and the offspring from the crosses the F1 (“first filial”) generation

8. Mendel’s Experiments
In the F1 generation, all the plants looked like just one of the parents.
It appeared that one trait had disappeared!
Two conclusions:
1. Biological inheritance is determined by factors that are passed from one generation to the next
Today these factors are called “genes”
Different forms of a gene are called “alleles”

9. Mendel’s Experiments Two conclusions (continued)
2. The principle of dominance: some alleles are dominant and others are recessive

10. Mendel’s Experiments Segregation
To discover if the recessive alleles were still present in the F1 generation, Mendel allowed the F1 plants to self-pollinate and produce an F2 generation
Result: The traits controlled by the recessive allele reappeared!
How? Alleles had been separated (“segregated”) from each other during gamete (sex cell) formation

11. Mendel’s experiments Segregation (continued)
The F1 plants inherited one allele from one parent and one allele from the other.
Example: If a short parent (tt) was crossed with a tall parent (TT), the offspring inherited one short allele (t) and one tall allele (T). Since it had a dominant and a recessive allele, the dominant trait (tall) was expressed. The F1 can produce two different types of gametes (those with an allele for tallness “T” and those with an allele for shortness “t”).