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

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

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

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

Research time: Examples of the different types of selection?

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

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.

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

Humans selected:

Humans selected:

Do the FIT necessarily get to reproduce more?

NON-RANDOM MATING

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

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

Mendel’s Experiment Gregor Mendel (1822-1884). 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

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

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

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

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

Practising Punnet Squares Y 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

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

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