1. The scientific study of heredity.
Genetics
The scientific study of heredity.

2. Vocabulary: Make sure to DEFINE these words as you go through the notes
Heredity Phenotype Variation Genotype Dominant DNA Recessive Allele Purebred Meiosis Hybrid Homozygous Heterozygous

3. What is Heredity ?
The passing of traits from parents to their offspring
Traits are passed to you through your parent’s sperm and egg
50% of DNA from mom, 50% from dad
Variation (differences in people’s traits) are due to the combination you inherit

4. 1860s: Gregor Mendel “Father of Genetics” (he was an Austrian monk)
He figured out how traits are passed on before we knew about DNA, or chromosomes or meiosis

5. To begin, Mendel created pure breeding plants
all pure purple
Purple
white
all pure white

6. First Cross: pure purple with pure white
Cross fertilized P (Parental) generation
Pure purple with pure white
P Generation F1 Generation
purple
white X
All purple

7. Second Cross: Cross 2 F1 plants
Cross fertilized two of the offspring of the F1 generation
purple
purple
purple
purple X
purple
white
These were the F2
This was always 3:1 ratio
or out of 929, 705 : 224

8. Mendel’s Experiments led him to 3 Laws of Inheritance
The Law of Dominance
The Law of Segregation
The Law of Independent Assortment

9. The Law of Dominance:
Each individual has TWO factors for each trait known as alleles
Some alleles dominate over others – the dominant allele is expressed in the offspring
Homologous chromosomes-same traits -different forms
These are alleles
Freckles
No Freckles
Dimples
No dimples
Tongue roller
Non-roller
From Mom
From Dad

10. Alleles are: Represented by a letter of the alphabet
Capital = dominant allele A
lowercase = recessive allele a
Each allele corresponds to a gene on a chromosome
- the alleles represent different forms of the gene

11. Law of Segregation
The two alleles for each trait separate and move into different gametes – meiosis
Since only one egg or one sperm will contribute to the new offspring, only one allele for a trait is passed on
The chance that any allele will be passed on is 50%

12. Law of Independent Assortment
the inheritance of alleles for one trait doesn’t affect the inheritance of alleles for another trait
- occurs in meiosis during metaphase 1

13. Meiosis: division of the sex cells

14. Genotype:
Genotype is the combination of alleles for a trait expressed with letters
Homozygous dominant (purebred)
TT - two capital letters
Heterozygous (hybrid)
Tt - one of each letter (big and small)
Homozygous recessive (purebred)
tt - two lower case letters

15. Phenotype:
Phenotype is physical expression of the genotype. (how it looks)
Genotype Phenotype
TT tall plant
Tt tall plant
*dominant allele always is expressed over the recessive allele
tt short plant
*recessive trait is expressed only if there is no dominant gene

16. If R = red, and r = white What is the genotype of homozygous dominant?
What is the heterozygous genotype? Rr
What is the homozygous recessive genotype? rr

17. If R=red and r =white What is the phenotype of of RR?
What is the phenotype of Rr?
What is the phenotype of rr?
White

18. If two parents are crossed (TT X tt), what are the resulting offspring?
You can determine phenotypes using a Punnet square. T T
parent Tt Tt t
Genotypes:
4 Tt Tt Tt
Phenotypes:
4 Tall t
This is the first or parent generation
parent

19. Now try on your paper a cross of two of the offspring from the parent generation. This is called the first generation or the F1. T t T Tt TT Tt tt t
Genotypes:
1TT: 2Tt : 1tt
Phenotypes:
3 Tall: 1 Short.