Genetics is the study of inherited traits and heredity, or the passing of traits from parents to offspring. Mendel conducted experiments with pea plants to understand heredity. He found that traits are controlled by discrete factors, now known as genes, and that dominant alleles hide recessive alleles without blending. When the offspring of his first experiment were allowed to reproduce, some showed the recessive trait, demonstrating that alleles separate and recombine according to the laws of segregation and independent assortment.

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 2nd
Experiment
• 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”