1. Fundamentals of Genetics

2. Introduction to Genetics
1. GREGOR MENDEL - “Father of Genetics”
Austrian monk, teacher, scientist, gardener
Formulated basic laws of heredity in the early 1860s
Used quantitative data

3. 2. Worked with garden peas because:
Easy to grow and had a short generation time
Could be self-pollinated
3. Chose true-breeding varieties for his experiments
NO genetic variation for a trait
Studied 7 simple traits

4. P1 = parental generation F1 = first-generation (sons/daughters)
4. Mendel cross-pollinated plants
P1 = parental generation
F1 = first-generation (sons/daughters)
F2 =second-generation

5. 5. Principle of Dominance and Recessiveness
F1 plants resembled only one of the parents
F1 hybrids contained two factors for each trait
one dominant; (stronger, masks recessive);
one recessive; (seems to disappear)

7. 6. Principle of Segregation
Organism contains two factors for each trait.
Factors segregate during formation of gametes.
Each gamete contains one factor for each trait.

8. 7. Principle of Independent Assortment
Each trait is independent of another
Genes of one pair of traits assort independently
All combinations of genes occur in gametes

9. Chromosomes, Genes, and Genetic Crosses
Homologous Chromosomes contain genes (locations) for the same traits
Traits are controlled by alleles (alternative forms of a gene).
Genotype refers to the alleles an individual receives at fertilization
Phenotype refers to the physical appearance
of the individual.

10. 5. Homozygous dominant genotypes =
two dominant alleles for a trait. (BB)
6. Homozygous recessive genotypes =
possess two recessive alleles for a trait (bb)
7. Heterozygous genotypes =
one of each allele for a particular trait (Bb)

11. Show probabilities of future offspring
8. Punnett Squares
Show probabilities of future offspring
Monohybrid crosses = crosses between
individuals that involve one pair of contrasting traits.

12. 9. Monohybrid Crosses (Examples)
Ex 1: Pure Tall x Pure Short
TT=Tall
tt =short F F2
T T t Tt Tt T t
T t TT tt
Genotype:
25% TT homozygous dom.
50% Tt heterozygous
25% tt homozygous rec.
Genotype: 100% Tt (heterozygous)
Phenotype: 100% Tall (hybrid tall)
Phenotype: 75% tall
25% short

13. 10. Test Crosses
A cross of an individual of unknown genotype with an individual of known genotype
Tells if individual is heterozygous or homozygous
Very important to breeders

15. STOP

16. Incomplete Dominance

17. Dominance Has Degrees 1. Incomplete dominance
Offspring are intermediate between two parental phenotypes
Neither allele is completely dominant over the other
Both alleles influence phenotype
3 phenotypes

18. Ex: Japanese Four o’clocks RR = red RR’ = pink R’R’ = white
All Pink
1 red : 2 pinks : 1 white

20. 2. Codominance
Both alleles of a gene are expressed.
A person with AB blood has both A and B antigens on their red blood cells.
Neither allele is dominant or recessive

21. RED
WHITE
ROAN

22. White & Red Mixed – RW (“roan”)
Ex: Red Coat - RR
White Coat – WW
White & Red Mixed – RW (“roan”)
R R
R W RW RW RW R W RR W RW RW RW WW
All Roan – both red and white hair
1 red : 2 roan : 1 white

23. STOP

24. Feather color = ORANGE or blue
Dihybrid Cross
 Feather color = ORANGE or blue
  CREST or no crest

25. A cross involving two pairs of
contrasting traits
Example:
Dominant Recessive
Yy, YY = yellow yy = green
Rr, RR = round rr = wrinkled

26. Example cont. P1 RRYY x rryy round, yellow wrinkled, green
(homozygous) (homozygous) RY RY ry
RrYy
RrYy ry
RrYy
RrYy
Offspring are all heterozygous

27. RrYy X RrYy Law of Independent Assortment
Genes for different traits are inherited independently
R, r, Y, y go to sperm/egg independently of each other
Can recombine in four ways:
RY, Ry, rY, ry

28. RY Ry rY ry
RRYY RY Ry rY ry

29. . 9 round,yellow : 3 round, green : 3 wrinkled, yellow : 9:3:3:1 1 wrinkled ,greenRY Ry rY ry RY
RRYY
RRYy
RrYY
RrYy Ry
RRYy
RRyy
RrYy
Rryy rY
RrYY
RrYy
rrYY
rrYy ry
RrYy
Rryy
rrYy
rryy