1. Observable Patterns of Inheritance
Mendelian Genetics

2. Early Ideas About Heredity
People knew that sperm and eggs transmitted information about traits
Blending theory: offspring were the combination or blend of their parents
Problem:
Would expect variation to disappear
Variation in traits persists

3. Gregor Mendel Strong background in plant breeding and mathematics
Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring

4. Why The Garden Pea Plant?
Easy to grow
Mature Quickly
Easily observable, contrasting traits
Easy to control pollination

6. Mendel’s First Experiment
He crossbred pure tall and pure short plants. These plants were called the parental generation (P).
This experiment is called a monohybrid cross because it focuses on only one inherited characteristic.
 Mendel's Hypothesis: Mendel expected to see offspring plants of medium height.

7. Mendel’s First Experiment
The hybrid offspring from P were called first filial generation (F1)‏
Mendel's Observations: all of the offspring were tall
 Mendel's Conclusion:
dominant trait = tallness, recessive trait = shortness,
the recessive trait is not expressed in first generation

8. Principle of Dominance
The Principle of Dominance:
When an organism is hybrid (cross bred) for a pair of contrasting traits, it shows only the dominant trait.

9. Mendel’s Second Experiment
Mendel allowed the F1 plants to mature and self-pollinate. Their offspring were called the second filial generation (F2).
Mendel's Observations:
¾ of the plants were tall, ¼ of the plants were short

10. Mendel’s Second Experiment
Mendel's Conclusion:
offspring inherit two “factors” for each characteristic (e.g. height), one from each parent,
the F1 DID inherit contrasting factors but only the dominant factor is expressed

11. Principle of Segregation
Hereditary characteristics are determined by distinct factors (genes) that occur in pairs.
These paired factors segregate from one another and are distributed into different sex cells.
Each sex cell has an equal probability of possessing either of the pair.

12. Genes Units of information about specific traits
Passed from parents to offspring
Each has a specific location (locus) on a chromosome

13. Alleles Different molecular forms of a gene Arise by mutation
Dominant allele masks a recessive allele that is paired with it

14. Allele Combinations Homozygous having two identical alleles at a locus
AA or aa
Heterozygous
having two different alleles at a locus Aa

15. Genotype & Phenotype
Genotype refers to particular genes an individual carries
Phenotype refers to an individual’s observable traits
Cannot always determine genotype by observing phenotype

16. Tracking Generations Parental generation P mates to produce
First-generation offspring F1
mate to produce
Second-generation offspring F2

17. Impact of Mendel’s Work
Mendel presented his results in 1865 to a small Austrian audience
Paper received little notice
Mendel discontinued his experiments in 1871
Paper rediscovered in 1900 and finally appreciated

18. Earlobe Variation
Whether a person is born with attached or detached earlobes depends on a single gene
Gene has two molecular forms (alleles)‏

19. Earlobe Variation
                             
You inherited one allele for this gene from each parent
Dominant allele specifies detached earlobes
Recessive allele specifies attached lobes
                             

20. Dominant & Recessive Alleles
If you have attached earlobes, you inherited two copies of the recessive allele (rr)‏
If you have detached earlobes, you may have either one or two copies of the dominant allele (RR or Rr)‏

21. Human Variation Some human traits occur as a few discrete types
Attached or detached earlobes
Many genetic disorders
Other traits show continuous variation
Height
Weight
Eye color

22. Handout on human traits
What is your phenotype?
What is your genotype?

23. r R

24. T t

25. H h

26. W w