1. Mendelian Genetics
Ch 14

2. Mendel Investigated variation in pea plants Studied traits in plants
Particulate theory of inheritance
Genes maintain integrity from generation to generation. Instead of blending together they act as discrete entities or particles.

3. Mendel’s laws Law of segregation
- The two members of each gene pair segregate or separate into different gamete cells during the formation of eggs and sperm
Law of independent assortment
The alleles of different genes are transmitted independently of each other

4. Mendel’s single factor cross
Single factor cross, focused on one trait – i.e. flower color
P – purebred parents,
WW x ww
F1 – all offspring were hybrid Ww
Monohybrid cross:
Ww x Ww
F2 – 3:1 ratio

5. Mendel’s two factor cross
Looked at 2 factors,
i.e. seed shape & color
P – purebred parents
F1 – all hybrids (for both factors)
Dihybrid cross:
RrYy x Rr Yy
Result: 9:3:3:1

6. 1 factor cross (monohybrid) practice
Axial flowers are dominant to terminal flowers
What are the genotypic & phenotypic ratios of a cross between a plant with heterozygous axial flowers and a plant with terminal flowers?
1. Choose letters to represent alleles
2. Write genotypes of parents
3. Write possible gametes for each parent
4. Set up and complete punnett square
5. Write genotypic ratio: DD: Dd: dd
6. Write phenotypic ratio: Dominant: recessive

7. Test cross To determine unknown parent with dominant phenotype
Cross with a recessive homozygote
Tall dominant to short in pea plants
A cross between tall plant and short plant produces ½ tall plants, ½ short plants. What is the genotype of the tall plant?

8. 2 Factor cross (Dihybrid) - practice
In rabbits Gray hair (G) is dominant to white (g), and Black eyes (B) are dominant to red (b).
Cross a heterozygous gray, red eyed rabbit with a homozygous gray, heterozygous black eyed rabbit; what is the phenotypic ratio?
Determine gametes (use FOIL)
Set up punnett square
Determine phenotypic ratio: D/D: D/R: R/D: R/R (D = dominant, R = recessive)

9. Codominance
Both alleles are expressed CRCR x CWCW – Red flower, white flower Offspring: CRCW – red & white flower

10. Incomplete dominance CRCR x CWCW – Red flower, white flower
Offspring: CRCW – hybrid is pink – inbetween two parents

11. Blood type Multiple alleles: IA, IB, i
Shows Codominance, as well as complete dominance

12. Multiple alleles – more than 2 alleles for a character

13. Epistasis – phenotypic expression of one gene is affected by another

14. Pleitropy – ability of a gene to affect an organism in many ways, i. e
Pleitropy – ability of a gene to affect an organism in many ways, i.e. sickle cell disease has multiple effects
Effects of Sickle Cell allele

15. Polygenic inheritance – multiple genes affect a single phenotypic character
Polygenic inheritance of skin color

16. Probability & Genetics
Rule of multiplication – probability that two or more independent events occur together
Multiply individual probabilities
Rule of addition – probability of an event that can occur in two or more different ways –
Add separate probabilities

17. ½ x ½ = ¼ Solving genetics problems by probability:
Hybrid Tall plants – Tt
What is the probability of each parent having the recessive allele?
1/2
What is the probability of the parents producing a short plant?
½ x ½ = ¼

18. Dihybrid cross YyRr x YyRr Can take each trait separately
Probability of yellow offspring:
YY, Yy = 3/4
green offspring:
yy = 1/4
Probability of round offspring:
RR, Rr = 3/4
wrinkled offspring:
rr = 1/4

19. Probability –
Yellow & round
¾ x ¾ = 9/16
yellow & wrinkled
¾ x ¼ = 3/16
green & round
¼ x ¾ = 3/16
green & wrinkled
¼ x ¼ = 1/16
Probability of yellow seed
9/16 + 3/16 = 12/16 = 3/4