2. Genetics
• What is genetics?
study of inherited traits - “heredity”
• What is heredity?
passing of traits from parents to offspring
(children)
• What is a trait?
feature an organism can pass on to
offspring ex) hair color, eye color, etc

3. Early Ideas - Heredity
• Originally believed…
child’s traits were
result of “blending
between parent’s
traits”
• Gregor Mendel
decided to test this
idea
• He knew nothing
about DNA

4. • Genes!
• Genes are…
segments DNA on
chromosome code for a
trait by the production of a
protein
• There are several genes on
each chromosome.

6. Mendel’s Pea Plants
Why did Mendel use
pea plants?
1) Several
contrasting traits
2) Understood
method reproduction

7. Mendel’s Experiments
• The 1st thing Mendel did was cross purebred plants…
• Purebred- produce young with same trait generation
after generation
• What will happen if cross plants with
different forms of a trait?
• Ex) trait – seed shape
forms – round or wrinkled seed shape

8. Mendel’s Experiments con’t
• Parental generation (P)
“original group”
• First filial generation
(F1) offspring of the
parental cross
• ALL offspring
resulted were ROUND

9. Mendel’s Conclusion
• “NO blending- no ½ round ½ wrinkled seeds”

10. We NOW know why…
• Many traits have 2 alleles
• Allele- 2 contrasting forms of a trait
ex) gene on chromosome for trait–seed shape
2 forms - round allele or wrinkled allele
• Principle of Dominance- one allele appears and
causes contrasting allele NOT to appear
• dominant allele - hides the other allele; capital
letter
• recessive allele- form often NOT expressed,

11. Mendel’s 2 Experiment
nd
• The next question Mendel wanted to answer was:
Why didn’t any of the recessive
characteristics like (wrinkled) show
up in the F1 generation?
• To answer this question Mendel extended his
experiment and allowed F1 to reproduce…

12. Mendel’s Results
• Second filial
generation (F2)-
offspring of F1
• Some offspring
showed recessive
trait, some the
dominant trait
3:1 ratio
(round:wrinkled)

13. Mendel’s Conclusion
• Why did the recessive trait disappear in the F1
and then reappear in some of the F2?
• The dominant allele hides the recessive allele in
the F1
• Since the recessive allele reappeared in the F2 it
must have “separated” from the dominant allele
• Law of Segregation- when gametes form alleles
for a trait are separated (each parent gives one
allele to offspring)

14. Mendel’s Results Summarized
• Every trait is controlled by at least 2 different factors (1 gene / 2 allele)
Use letters to represent contrasting forms (alleles) for a trait
Example: Trait: Seed Color (letter Y)
Y = yellow (dominant allele)
y = green (recessive allele)
• Alleles occur in pairs (1 mom/1 dad)
• YY homozygous dominant – 2 same letter - capital
Yy heterozygous – 2 different letters
yy homozygous recessive - 2 same letter - lowercase
• Phenotype - outward appearance/physical characteristic
• Genotype - genetic makeup “letters”