1. The Basics of Genetics
GENETICS- The science of heredity and variation in living organisms
Heredity- the passing of traits from parents to offspring
Traits- different physical characteristics
(tall, short, brown hair, blond hair, red flowers, pink flowers)
Sid Galloway

2. *P Generation = Parental generation *F1 Generation = First generation
*F2 Generation= Second generation
Sid Galloway

3. Genes = factors that control traits. (Example: plant height)
Alleles = different forms of a gene.
(Examples: tall or short) Tt
One allele from dad
(t)
One allele from mom
(T)
Sid Galloway

4. www.soulcare.org Sid Galloway

5. Alleles
* Dominant allele = one whose trait always shows up if it is in the genes.
Always written as capital letters.
* Recessive allele = is masked or covered up, if a dominant allele is in the genes.
Always written as small letters of the dominant allele
Sid Galloway

6. Symbols in Genetics * Capital letter = dominant (T = tall)
* Lowercase letter = recessive (t = short)
-TT =homozygous with two dominant alleles
(tall plant)
- tt = homozygous with two recessive alleles (short plant)
-Tt = heterozygous with 1dominant & 1 recessive (tall plant)
Sid Galloway

7. *Heterozygous= have two different alleles for a trait
tall from mom and short from dad (Tt)
*Homozygous= have two of the same alleles for a trait
tall from mom and tall from dad (TT)
short from mom and short from dad (tt)
Sid Galloway

8. www.soulcare.org Sid Galloway

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10. Genotype and Phenotype
Genotype: The genetic make up for a specific trait.
TT or Tt
Phenotype: The appearance of a specific trait.
TT- tall plant tt- short plant
Sid Galloway

11. Gregor Mendel- father of Genetics
He experimented with pea plants:
-First he crossed homozygous tall (TT) with homozygous short (tt). (parental generation)
-All offspring (F1) were heterozygous: Tt TT x tt = Tt
-All were tall.
Sid Galloway

12. Gregor Mendel and his peas
Then he crossed (bred) the F1 generation:
Tt x Tt
When heterozygous F1 were crossed Tt x Tt, some of the offspring were Tall (TT and Tt) while few were short (tt).
Tt x Tt = TT, Tt and tt
Mendel experimented with many different traits of the pea plants
Sid Galloway

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14. Punnett
Square
Sid Galloway

15. Problem:
If we cross a homozygous tall plant by a homozygous short plant what will the offspring look like?
We can attempt to answer this question using
five steps:
1. Define the letters
2. Define the cross
3. Complete the Punnett Square
4. Find Genotypic ratios
5. Find Phenotypic ratios

16. 1. Define the letters: 2. Define the Cross:
Homozygous Tall = TT
Homozygous Short = tt
2. Define the Cross:
TT x tt

17. 3. Complete the Punnett Square

18. 3. Find the Genotype Ratio:Tt Tt
The Genotype is the genetic makeup- How many of each letter combination? t Tt Tt
TT =
Tt =
tt =
0/4
So the genotypic ratio is:
TT:Tt:tt
0 : 4 : 0
4/4
0/4

19. 3. Find the Phenotypic Ratio:
The Phenotype is the physical appearance What letter combinations make Tall? t Tt Tt t Tt Tt
Short? tt TT Tt
So the
phenotypic ratio would be Tall:Short
4 : 0
How many are tall?
4 /4
How many are short?
0 /4

20. Follow steps 1-5 to figure this out with your table group
Now you try one
Problem:
If we cross two heterozygous tall plants what will the offspring look like?
Follow steps 1-5 to figure this out with your table group

21. Using your Text book: (pg. 272)
1. Explain the difference between:
Incomplete Dominance and Codominance
*Explain the difference in words but also show an example of each of these using a problem and the five steps that we have used before. (punnett square)
2. What is a polygenic Trait? What human traits do you think are polygenic?