1. Introduction to Heredity
Passing On Information
Section 5.1

2. Early Ideas Hippocrates (460-377 BCE)  seeds
Aristotle ( BCE)  male and female semen
Helps us determine the likelyhood of inheriting certain traits

3. More Early Ideas William Harvey (1500’s)  epigenesis
Stages of development based on mother’s experience
Anton van Leeuwenhoek (late 1600’s)  “animalcules”

4. Even More Early Ideas 19th century  “blending theory” Charles Darwin
sperm and egg mixed
Result was a blend
Had a lot of holes
Charles Darwin
Offspring had variations of parents’ traits
Natural Selection

5. Finally an Answer… Gregor Medel (1822 – 1884), an Austrian monk
Experimented on pea plants
3 reasons:
Grow quickly
Pollinate easily
Definable traits
Found 7 traits that had only two possible variations
1. Choosing an appropriate organism to study, 2. designing and performing the experiment correctly, 3. analyzing data properly

6. 7 Traits Seed shape Seed colour Flower colour Flower position
Pod colour
Pod shape
Height
yellow
purple
green
inflated
tall
round
axial (side)
white
Terminal (side)
yellow
Constric-ted
short
Wrink-led
green

7. Setting Up Mendel’s Experiment
Needed a purebred
How could he achieve this?
Ended up with 14 purebreds
Called process “true breeding”
Purebred  desceding from a line of similar traits
True breeding  breed two tall plants together that are tall (babies are 5 T 3 t), then breed two of those 2 tall ones breed (they have 4 T and 1 short)  keep going until all offspring are tall

8. Mendel’s First Experiment: A Monohybrid Cross
P (Parent) generation
Crossed pure tall with pure short
Actual: 100% tall!
Called them Filial generation or F1 generation
Hybrid (a cross between two purebreds)
Monohybrid (only one trait was involved)

9. Seed of F1 What actually HAPPENED in the seeds?
Knew the seeds HAD to be hybrids
Principle of Dominance
Dominant trait is always expressed
Recessive is present but not expressed
What would blending predict
Dominant trait is always expressed
Recessive is latent (present but not expressed)  may be expressed if it’s the only trait present

10. The Next Generation Crossed two F1s  F2 generation Expected results?
75% tall, 25% short
Mendelian ratio (3:1)

11. Definitions Gene vs Allele We use letters to represent alleles
T = tall
t = short
What are the allele’s P generation
Tall plants = TT
Short plants = tt
Homozygous
Alternate  options
Recess not altered and can still be passed on
Gene represent the trait, allele represent what it could actually be (options)
Homozygous = two alleles are the same

12. Hybrids Offspring (F1)generation Called these hybrids
Heterozygous (Tt)
Heterozygous means different or one of each

13. Mendel’s Conclusions Each parent starts with two hereditary genes
These genes separate
Only one is passed on to an offspring
If the dominant gene is present in the offspring, it is expressed (regardless of recessive trait)
Recessive gene expressed only if both recessive genes are present
Part of chromosome that gives information about what trait should be expressed
Ex. Gene for hair colour

14. Law of Segregation Law of Segregation states that:
Inherited traits are determined by pairs of genes
These genes segregate into gametes, with one gene in each
We now know this is a result of: ___________
One from Dad, one from Mom
They go through Meiosis, but they didn’t know that yet