1. Chapter 11 Introduction to Genetics
Mendel

2. Gregor Mendel (1850) Did extensive studies on pea plant traits
Documented traits and inheritance patterns of thousands of plants
Keep in mind that DNA had not been discovered
What he called “factors” we know to be genes, which code for particular traits

3. Monastery Garden Work Mendel was in charge of the garden
He really liked pea plants
He had a stock of TRUE BREEDING plants
If allowed to self pollinate they would always produce offspring identical to themselves
However pea plants can also cross pollinate
Mendel controlled this to produce certain TRAITS (specific characteristics)

4. Basic Terminology Genetics – the study of heredity
Heredity – the passing of traits from parents to offspring
Trait – any characteristics that can be passed from parents to offspring
examples: dimples & freckles
Genes - a segment of DNA that codes for a specific trait
Hybrid – cross between parents with different traits

5. Alleles Alleles are slightly different forms of a gene
The sequence of nitrogen bases may be slightly different
A person has 2 alleles for each trait
Occur on homologous chromosomes
Of the 2 alleles, you receive one from your mother and one from your father during fertilization

6. Types of Alleles
Dominant Allele – the allele that is expressed; the stronger allele
Symbolized by a capital letter
Recessive Allele – the allele that is only expressed if two of them are present; weaker allele
Symbolized by a lower case letter

7. Types of Alleles Example: Freckles = Dominant No Freckles = Recessive
Dominant Allele = F
Recessive Allele = f
Dimples = Dominant
No Dimples = Recessive
Dominant Allele = D
Recessive Allele = d

8. Genotypes & Phenotypes
Genotypes are the genetic make-up of an organism
What do the alleles look like: DD Dd dd
Phenotypes are the physical appearance of a trait
sometimes appear different due to environmental factors
having dimples
having freckles
no dimples
no freckles

9. Genotypes & Phenotypes
Definitions
Abbreviations
Phenotype
Homozygous Dominant
2 Dominant Alleles FF
Freckles

10. Genotypes & Phenotypes
Definitions
Abbreviations
Phenotype
Homozygous Dominant
2 Dominant Alleles FF
Freckles
Heterozygous
1 Dominant Allele;
1 Recessive Allele Ff

11. Genotypes & Phenotypes
Definitions
Abbreviations
Phenotype
Homozygous Dominant
2 Dominant Alleles FF
Freckles
Heterozygous
1 Dominant Allele;
1 Recessive Allele Ff
Homozygous Recessive
2 Recessive Alleles ff
No Freckle

12. Principles of Mendel Mendel develop 3 principles that hold true today
Principle of Dominance and Recessiveness
Principle of Segregation
Principle of Independent Assortment

13. Principles of Mendel Principle of Dominance and Recessiveness
One factor in a heterozygous pair may mask the other factor
The factor that is expressed is dominant, the one that is masked (not expressed) is recessive
In order for a recessive trait to be expressed, the organism must have a homozygous recessive genotype

14. Principles of Mendel Principle of Segregation
Gametes (sperm and egg) are formed during the process of meiosis
Each gamete receives only one allele for each trait

15. Principles of Mendel Principle of Independent Assortment
Alleles segregate into gametes randomly and independently of each other
Therefore each egg (or sperm) cell should be different from the another egg (or sperm) cell

16. Mendel
Unit 9, Part 2 Notes