NATURAL SELECTION ***READ 8.1*** What was happening in the video? What kind of selection is this? http://www.youtube.com/watch?v=nS1tEnfkk6M ***READ 8.1***

Types of Selection Directional Selection: when selection favour individuals with a more extreme variation of a trait; selection that favours an increase or decrease in the value of a trait from the current population average.

Types of Selection Stabilizing Selection: occurs when the average phenotype within a population is favoured by the environment; selection against individuals exhibiting traits that deviate from the current population average. This is human birth weights Birth weights are variable because it is heritable According to natural selection, babies born at weights offering the best chance of survival should be more numerous Around 6-7 lbs are where mortality rates are the lowest and most babies survive Less than 6lbs are premature and heavier babies often experience birth-related complications

Types of Selection

Types of Selection Disruptive Selection: selection that favours two or more variations of a trait that differ from the current population average; favours individuals with variations at opposite extremes of a trait over individuals with intermediate variations.

Types of Selection

Types of Selection Sexual Selection: differential reproductive success caused by variation in the ability to obtain mates; results in sexual dimorphism, and mating and courtship behaviours. Ask them what they think is attractive and what they do to impress girls (cars, money, athletic, smart) Might be a dance In this society what is beautiful? Talk about in the philippines, ask about where their from, or their certain culture

Types of Selection (Sexual) Favours any trait that enhances the mating success of an individual Ie. Evolving appearances and behaviours that are quite different in males and females Ex. Male-male competition These traits might be a disadvantage when it comes to predators (bright colours, distinctive song) Also with plants: attract pollinators

Altruism At times, animals behave in ways that reduce their individual fitness and increase the fitness of others “helping others” There are two types of Altruism: Kin Selection Group Selection Talk about how I don’t want to raise kids but how I love and babysit cousins and nephews and nieces sometimes

Kin Selection Helping relatives to survive and reproduce even if it means forgoing breeding yourself You share 50% of your genes with each parents and 50% with a sibling If an individual forgoes breeding and instead helps raise a close relative, it is helping pass on a portion of its own genes to the next generation The more closely related an individual is to another, the more likely it is to forego a breeding attempt

Group Selection “for the good of the group” In social populations, small groups will compete with other small groups for resources Any adaptation that would improve a group’s survival over another group would also improve the individuals survival even if it doesn’t directly benefit the individual By cooperating with each other they ensure each other’s survival

Himalayans = 40% oxygen level compared to sea level When people from the lowlands are up in the mountains, red blood cell count increases but makes the blood more viscous Places stress on the heart = reduced fertility = increased child mortality Tibetans who live at high altitudes don’t have an elevated red blood cell count but don’t have difficulty coping with loe oxygen levels Genetic mutations = increase oxygen carrying capacity of their blood while maintaining normal red blood cell counts MICE: chose only those individuals who ran the most on the wheel 10 generations later, mice exhibited much higher running distances and average speeds compared to control populations What is this an example of that we already learned about? Artificial selection, selective breeding

Evolutionary Change without Selection Genetic Drift: changes to allele frequency as a result of chance; such changes are much more pronounced in small populations Random shifting of the genetic makeup of the next generation When individuals produce offspring, the chances of passing on a particular allele is subject to random chance In small populations Can result in a particular allele can be very common or disappear entirely When it disappears, it reduces genetic diversity Ask class what they think of when i say “bottleneck effect”, and founder effect

1. BOTTLENECK EFFECT Bottleneck: a dramatic, often temporary reduction in population size, usually resulting in significant genetic drift Loss in genetic diversity after an extreme reduction in population size Can have adverse consequences Seals, cheetah (7) - don’t know what happened but 10 000 years ago there was estimated to be only 7 of them left Low reproductive success and high juvenile mortality rates Northern elephant seal – 20 of them in the 1890s because of overhunting

2. FOUNDER EFFECT Founder effect: genetic drift that results when a small number of individuals separate from their original population and establish a new population Initial population would have a different mix of alleles, by chance alone Populations from bottleneck and founder effects are subject to the effects genetic drift Further increases the chances that their gene pool will differ from the original population

Big Horn Sheep 1975: 20 sheep 1999: ~650 sheep

HARDY-WEINBERG PRINCIPLE The Hardy-Weinberg Principle: in large populations in which only random chance is at work, allele frequencies are expected to remain constant from generation to generation Any factor that causes allele frequencies to chance leads to evolutionary change Two mathematicians, Godfrey Hardy and Wilhelm Weinberg, used mathematical reasoning to explain the relationships between allele frequencies within a population and the chances those frequencies will remain constant (explain, don’t put into note)

HARDY-WEINBERG PRINCIPLE These conditions lead to evolution Natural selection: favours the passing of some alleles over others Small population size: increases the likelihood of genetic drift Mutation: introduced new alleles to a population Immigration/emigration: introduces or removes alleles in a population Horizontal gene transfer: the gaining of new alleles from a different species