welcome to ap daily this is mr birth from union high school in vancouver washington today's topic is 7.4 population genetics so what will we be learning today for today's lesson we'll be looking at what factors drive evolution how do mutations contribute to natural selection how does genetic drift impact population size and then finally how does the reduction of genetic variation impact populations of the same species so let's dive in evolution is driven by random occurrences a mutation is a random change in an organism's genome it's an alteration in a dna sequence it can contribute to changes in the genetic makeup of a population over time it creates genetic variation within a population and provides new phenotypes that contribute to evolution by natural selection reduction of genetic variation can increase the differences between populations of the same species genetic drift refers to the random change in the frequency of a particular allele within a population it is a non-selective process generally occurring in small population there's an increased death rates and low reproductive rates natural catastrophes such as fires and volcanic eruptions can cause this small population bottleneck events can contribute to genetic drift a large diverse population suddenly is reduced to a small population so in the picture you can see a bottleneck event occurs and what happens is a size of the population is severely reduced like stated before genetic drift is a non-selective process occurring in small populations founder effect refers to a random process that reduces genetic variation within a small population due to separation from a larger population migration and geological events can isolate populations the genetic makeup of a founder population can be different from the original population so as shown in the picture a small group of individuals breaks off from a larger population and establishes a colony migration or gene flow is the movement of individuals between populations causing an exchange of alleles between populations it introduces new genes into populations resulting in increases in genetic variation continued migration between populations reduces genetic diversity between populations over time so random processes play a role in the evolution of specific populations genetic variation is the raw material of evolution fitness is relative to specific environmental conditions so as conditions change fitness can change different phenotypes can be selected for or against according to changes in the environment and then finally evolution of a population cannot occur if there is no genetic variation within the population so let's practice for today's practice we're going to focus on stating the null and alternative hypothesis or predicting the results of an experiment a null hypothesis is one in which states experimental variables have no relationship and experimental observations are the result of chance an alternative hypothesis is one of several hypotheses stating experimental variables have a relationship and the experimental observations are a result of some non-random cause so let's practice please pause your video read the question and formulate your answer when you're ready push play again welcome back for this question you're looking at which of the following is a valid null hypothesis for this investigation involved involving northern spotted owls your answer should have been b spotted owls will continue to nest in the area where the barred owl songs are being played so what should you take away from this lesson for this lesson number one evolution is driven by random occurrences next mutation is a random process that results in genetic variation which provides phenotypes on which natural selection acts and contributes to evolution three genetic drift is a non-selective process occurring in small populations through bottleneck and founder effects and finally the reduction of genetic variation within a given population can increase the differences between populations of the same species well i hope this video has been helpful until next time thank you