AP BiologyEnduring Understanding 1A

Change in genetic makeup of a population over time is

evolution.

Natural Selection is a major mechanism of evolution

Natural Selection – in a population, organisms with a genetic trait that increases the chance of having offspring will pass on their genes to the next generation more than those without.Reproductive Fitness – relative ability to survive and leave offspring

Requirements1. More offspring born than can survive to

adulthood2. Competition for resources3. Genetic variation/diversity within the

population4. Some varieties have an increased chance to

survive long enough to reproduce.

Genetic variation and mutation play roles in natural selection. A diverse gene pool is important for the survival of a species in a changing environment.

Environments can be more or less stable or fluctuating, and this affects evolutionary rate and direction; different genetic variations can be selected in each generation.

An adaptation is a genetic variation that is favored by selection and is manifested as a trait that provides an advantage to an organism in a particular environment.

In addition to natural selection, chance and random events can influence the evolutionary process, especially for small populations.

Mathematical approaches are used to calculate changes in allele frequency, providing evidence for the occurrence of evolution in a population.This can be done using the Hardy-Weinberg Principle

The Hardy-Weinberg Principle

The Hardy-Weinberg law is an algebraic formula to estimate the frequency of a dominant or recessive gene in a population based on the frequency with which the trait or condition is found in a population.

A population with:1. A large number of individuals2. No migration3. No mutations4. Random mating5. No natural selectionIs said to be in Hardy-Weinberg equilibrium and no evolution can occur.

The equation is p2 + 2pq + q2 = 1 where:p = the frequency of the dominant alleleq = the frequency of the recessive allelep2 = the frequency of the homozygous dominant genotype2pq = the frequency of the heterozygous genotype.p2 = the frequency of the homozygous recessive genotype.

Cystic fibrosis is a genetic disorder in homozygous recessives that causes death during the teenage years. If 4 in 10,000 newborn babies have the disease, what are the expectedfrequencies of the three genotypes in newborns, assuming the population is at Hardy-Weinberg equilibrium? Why is this assumption not strictly correct?

The allele y occurs with a frequency of 0.8 in a population of clams. Give the frequency ofgenotypes YY, Yy, and yy. Show your work!

In the year 2374, humans finally developed the technology necessary for time travels. You are a scientist interested in the population genetics of extinct animals. Taking advantage of this technological advance, you decide to go to the past 8 million years to conduct a field work in Venezuela to study a population of Phoberomys pattersoni*, the world’s largest extinct rodent weighing approximately 700 kg (1500 lb) and looking vaguely like a giant guinea pig. The coat color of this rodent varies between tan (dominant) and brown (recessive). Assume the population is in Hardy-Weinberg equilibrium. You observed 336 tan Phoberomys and 64brown Phoberomys during your study.

a) What is the frequency of the homozygous recessive genotype?b) What is the allelic frequency of the dominant (tan) allele in the population?c) Of the animals you observed, how many were heterozygous?

You make another trip to Venezuela and this time you observe 650 animals.d) How many of the 650 animals would you expect to be tan, assuming the population is still in Hardy-Weinberg equilibrium?e) How many of these tan animals are homozygous for the dominant allele?f) How many of these 650 animals would you expect to be brown, assuming the population is still in Hardy-Weinberg equilibrium?

Key Vocabulary

1. Biological Evolution2. Natural Selection3. Reproductive Fitness4. Competition5. Variation6. Adaptation7. Hardy-Weinberg Principle8. Genetic equilibrium9. Hardy-Weinberg Conditions10. Hardy-Weinberg Equation