1. Genetics

2. Prehistoric Pooches
Dogs and humans have been companions for thousands of years. The domestication of dogs may have been one of the earliest human experiences with genetics.

3. Genetics - scientific study of how traits are passed from parent to offspring
Millions of years ago there were no dogs. Today’s domestic dogs are descended from a wild, wolfish ancestor.
Certain wolves were selected to mate which affected the traits that were passed from the parents to the pups.

4. Trait – a characteristic that can be passed on
With each generation, the traits of the wolves living with humans became more distinct from the traits of the wild wolves. Eventually, this led to a new breed – the domestic dog.

5. We’ve known for centuries that traits are passed from parent to offspring, but we haven’t always known how those traits are determined.
Blending Hypothesis – traits of parents were blended in the offspring

6. Chromosomes and cell division
The chromosomes make copies of themselves and then pass those on to the daughter cells.
We know that traits are passed on in these chromosomes but the relationship between chromosomes and traits was not always understood.

7. Gregor Mendel Austrian monk in 1860’s Experimented with pea plants
- Structure of pea flowers
- Traits showed obvious
differences that were
easy to see
- Reproduced quickly

8. Mendel’s Experiments

9. Structure of pea plants
the relatively closed structure of the pea flower petals makes it very easy for pollen from the anther to fertilize the pistil of the same flower
Self-fertilization
What’s the difference between self fertilization and asexual reproduction? Are they the same?

10. Structure of pea plants
Purebred – receives same genetic traits from both parents
Hybrid – receives different forms of a trait from each parent
Cross-pollination

11. Traits are easy to see
Mendel studied 7 traits that only come in 2 distinct forms
Example: pea pods were either yellow or green (there were no in-between colors)

13. Short reproductive cycle - 90 days
Quick results
Could repeat the experiments many times

14. Mendel’s Observations

15. Mendel began his experiments using two different purebred plants
P – the parental generation or first group to fertilize
F1 – the filial generation or offspring
F2 – the offspring of the F1 generation

16. Findings:
When crossing 2 different purebred parents, F1 generation were only one form of the trait
F2 generation showed % of F1 trait, and % of other trait P F1 F2
What should have happened according to the blending hypothesis?

17. Repeated his experiments with the other 6 traits

18. Mendel’s Conclusions

19. Blending hypothesis was wrong – forms of a trait must remain separate in offspring

20. Genes – sections of a chromosome that code for a trait
Allele – distinct form of a gene

21. Dominant allele – form of a gene that is fully expressed when two different alleles are present
Recessive allele – form of a gene that is not expressed when paired with a dominant allele

22. Unnoticed
Mendel performed these experiments for 8 years and published his work. Unfortunately, at the time scientists were focused on the work of Charles Darwin and so Mendel’s work went unnoticed for the next 37 years.

23. Walter S. Sutton
Observed stained cells under a microscope and noticed that the chromosomes acted like Mendel’s factors.

24. Chromosome Theory of Heredity
material of inheritance is carried by the genes in chromosomes
To help explain the new theory, scientists came up with some new terms and symbols

25. Gene – section of chromosome that code for traits
Allele – different forms of that trait
Pea color is controlled by a single gene with two alleles – one for green and one for yellow

26. Letters are used… Dominant allele – capital letter
- Example: Yellow is the dominant pea
color and would be represented by Y
Recessive allele – lowercase letter
- Example: green is the recessive pea color
and would be represented by y

27. What letters would be used for other traits?

28. Genotype the genetic makeup of an organism (YY, Yy, yy)
It includes both genes in a homologous pair of chromosomes

29. Phenotype
the physical appearance (yellow, green)

30. Homozygous
the two alleles in a gene are identical (YY or yy)

31. Heterozygous
the two alleles in a gene are different (Yy)

32. Mendel’s Laws

33. Law of Segregation each pair of genes separates during meiosis
F1 generation Meiosis Meiosis 2

34. Law of Independent Assortment
gene pairs separate into gametes randomly and independently of each other P p PP Pp pp

35. Law of Dominance
the dominant allele is expressed and the recessive allele is hidden. The recessive allele is only expressed when no dominant allele is present.