1. Heredity and Genetics

2. PRINCIPLES OF GENETICS
OVERVIEW
“Like produces like, but not *exactly* like”
REVIEW: Sexual reproduction → variation due to chromosomes
*HEREDITY: transmission of traits from parents to offspring
*GENETICS: science of heredity

3. A History Lesson *Gregor Mendel: 1822-1884
*monk in Czechoslovakia
*Vienna- studied science and math- became a teacher
*2 yrs later- returned to monastery; plant experiments
*1866- published data from 8 years of experiments
*1900- finally genetics recognized as major development
*Mendel’s Experiments:
*Studied pea plants (b/c clearly express traits like flower color, seed shape, seed color, and plant height)
*large sample sizes- help ensure actual ratios present in population

4. *crossed “different” plants → ex. Purple flowers x white flowers
*offspring of parental cross = first filial generation (F1)
*offspring of 2nd cross = 2nd filial generation (F2)
*Mendel produced 929 offspring– 705 were purple (3:1 ratio)
*DOMINANT TRAIT: form of a trait that dominates another trait; (prevents expression of another trait) (ex. Purple flowers)
*appears in F1 generation
*RECESSIVE TRAIT: hidden in F1 generation

5. *MENDEL’S HYPOTHESIS:
*Mendel’s experiments saw recessive trait disappear in F1
generation but reappear in F2 generation
*ASSUMPTION: for each trait, there must be a pair of factors- 1 comes from egg; 1 from sperm
* “Factors” = GENES: contain information for every trait
*Represented by symbols or letters
*Capitals = dominant
*lowercase = recessive
EX. W= purple, w= white

6. *ASSUMPTION: 2 genes segregate during gamete formation
*offspring = ratio depending on genes present
EX.
WW x ww parents
Ww Ww Ww Ww F1
Ww x Ww
WW Ww Ww ww F2
RESULTS: 1WW : 2Ww: 1ww
3 purple: 1 white (similar to 705: 929)

7. WW Ww ww *EASIER TO SEE WITH PUNNETT SQUARES:
*Chart used to determine possible combinations of genes among offspring
Gametes of 1 parent
Gametes of 1 parent
W w
EX: Ww x Ww W w WW Ww ww

8. *****50% white: 50% purple!!! *TEST OF SEGREGATION: 3:1 ratio 1st time
but what if Ww x ww???
MAKE YOUR PUNNETT SQUARE:
W w w Ww ww
*****50% white:
50% purple!!! w Ww ww

10. GENETICS TERMINOLOGY
*ALLELE: either of 2 alternative forms of gene for particular trait
ex. W or w
*GENOTYPE: combo. of alleles for certain trait
ex. WW, Ww, or ww
*PHENOTYPE: appearance of trait
ex. “purple” or “white”
*HOMOZYGOUS: 2 of same alleles for given trait
ex. RR, rr (deals w/ seed shape) or WW or ww
*HOMOZYGOUS DOMINANT: 2 dominant alleles (WW)
*HOMOZYGOUS RECESSIVE: 2 recessive alleles (ww)
*HETEROZYGOUS: 2 different alleles for a trait
ex. Rr or Ww

11. Pedigree charts
*are used to help determine the possible genotypes of parents and offspring

13. *are used to analyze the chromosomes present in a person
karyotypes
*are used to analyze the chromosomes present in a person

14. TIME TO PRACTICE
PUNNETT SQUARES!!