1. Natural Selection Who or what selects if an organism survives?
What is the “Selective pressure?”
What organism is selected?

2. Lamarck vs. Darwin Lamarck Darwin
Environment causes giraffes to stretch their necks over their lifetime to better survive.
Darwin
Environment selected that giraffes born with longer necks had a greater chance of survival

3. Natural Selection Variation. Inheritance.
Differential reproduction / “Struggle for existence”
Differential adaptedness

4. Types of Selection 1. Directional 2. Stabilizing 3. Disruptive
One extreme form of a trait is favoured
2. Stabilizing
Intermediate form of a trait is favoured
3. Disruptive
Both extreme forms of a trait are favoured

5. Research time: Examples of the different types of selection?

6. Genes: Unit of Variation
Genes are the carriers of inheritable traits
Mutations create new traits (new genes)
Mutations to germinal cells (i.e. sperm & egg) are hereditary
Somatic mutations (i.e. skin cells) are not
Sexual reproduction shuffles existing traits to create new combinations.
Environment selects for or against these new traits or combinations

7. So, how does Selection work on genes?
Population
A group of organisms of the same species and living in the same area
Therefore, sharing the same gene pool
Evolution works on populations not on individual organisms
Selection shifts the relative frequency and abundance of alleles in a gene pool
The Genetic definition of evolution:
Any change in the relative frequency of alleles in the gene pool of a population.

8. Artificial selection Also called “Selective Breeding”
Selective pressure = ?
Variation increased or decreased?
Problems?

9. Humans selected:

10. Humans selected:

11. Do the FIT necessarily get to reproduce more?

12. NON-RANDOM MATING

13. Non-random Mating Also known as “Sexual Selection”
Some organisms are more desirable mates than others.
Make themselves attractive to the opposite sex
Fighting off same-sex rivals
Organisms with this desirable trait are more likely to mate and produce offspring with similar characteristics
“Inbreeding”
Desirable trait may not improve fitness

14. Sex mixes things around!
Invented 2 billion years ago
Increased variation: unique individuals produced
Shuffling of DNA

15. Mendel’s Experiment
Gregor Mendel ( ).
Experimented with Pea Plant breeding.
Focused on 7 well-defined garden pea traits one at a time
Genotype = collection of genes (and alleles) in an organism
Phenotype = observable properties of an organism

16. Mendel’s 7 garden pea characters.
Seed shape
Seed color
Pod shape
Pod color
Mendel’s 7 garden pea characters.
Flower color
Flower location
Plant size

17. Monohybrid Cross Purebred tall × Purebred short
When he bred a purebred tall plant with a purebred short plant, all off the offspring were tall
Purebred tall ×
Purebred short
F1 generation = all tall
“Filius:” Latin for “son”
Then, when he bred two plants of the new generation together, he would get 1 short plant for every 3 tall plants. F1 × F1
F2 generation = 3 tall : 1 short

18. Mendel’s Conclusions
Hereditary particles (genes) exist in all living organisms and remain unchanged in an organism even if they are not expressed or seen.
“Shortness” disappeared in F1 and reappeared in F2. Shortness must therefore have still been present in F1
Each organism must contain two gene copies for each trait.
One form of the gene is Dominant, the other is Recessive.
The F1 were all tall even though one parent was short. Tall must therefore be dominant

19. Monohybrid Cross - explained
Parental generation:
“Homozygous” TT × tt
F1 = all Tt
F1-generation:
“Heterozygous” Tt × Tt T t TT Tt tt
This is called a Punnett’s Square
F2 phenotypic ratio = 3:1; genotypic ratio = 1:2:1

20. Practising Punnet SquaresY y Yy
Hh × Hh
YY × yy
Try these if you can:
AABB × aabb for F1 & F2
Phenotypic Ratio 4:0
Genotypic Ratio 4:0 H h HH Hh hh
Phenotypic Ratio 3:1
Genotypic Ratio 1:2:1

21. More practice for punnett squares
Phenotypic Ratio 3:1
Genotypic Ratio
4:8:4 or
1:2:1 for both A and B
4 AA’s
8 Aa’s
4 aa’s
4 BB’s
8 Bb’s
4 bb’s

22. Mendel’s Theories
Genes for different traits are inherited independently of each other.
Some exceptions, of course, occur
Incomplete Dominance (blending) for some traits
Codominance (random mixing)
Some genes are sex-linked