AP Biology Discussion Notes Monday 4/18/2016

Goals for the day Begin being able to think about how population genetics changes & why it changes Be able to explain & apply the Hardy-Weinberg Equilibrium Be able to understand, describe, & recognize what it means when genes are “linked”

Question(s) of the day 4/18 What is a linked-gene? How might you recognize one in a cross? What is not happening between linked genes? Punnett square represents meiosis & fertilization – sexual reproduction in organisms.

Fly lab Assumptions: Wild type (+) – Assume dominance ordered flies are Purebred Traits are Autosomal Basic & Complete Dominance All traits are Non-lethal Mendel’s Laws are at work Law of segregation Law of independent assortment Need to pay attention to directions just as though we were doing a real lab – the point is to save you time and energy – so it is to your benefit to listen.

FLY Lab DUE FRIDAY

Basic review – write in Notes under POPULATION GENETICS What term would you use for a change in a population? When we say a population changes, what is actually changing? what are some possible mechanisms of that change?

Population Genetics

Hardy-Weinberg Equilibrium Both gene frequency and genotype frequency will remain unchanged (in equilibrium) unless outside forces change those frequencies.

Hardy-Weinberg Equilibrium For the H-W Equilibrium to be operational, the following restrictions(Assumptions) must be in place: Mating must be completely RANDOM. There can be NO mutation. There can be NO immigration or emigration. The population must be “large” (in fact, infinitely large). There can be NO Natural selection operating on the population. [No fitness (______ & ________) advantage to any genotype/phenotype!]

Hardy-Weinberg Equilibrium Let’s think: what are things that could break these assumptions? Come up with 1 thing or 1 scenario that would break each assumption and write each on a space below.

Breaking Assumptions: #1 Mating must be completely RANDOM. Mating is not Random

Sexual dimorphism

Breaking Assumptions: #2 There can be NO mutation.

Breaking Assumptions: #3 There can be NO immigration or emigration.

Breaking Assumptions: #4 The population must be “large” (infinitely)

Breaking Assumptions: #5 There can be NO NATURAL selection operating [No fitness (survival & reproductive) advantage to any genotype/phenotype!]

So why even have these assumptions? What do they say when you Assume things?

Hardy-Weinberg Equilibrium What the H-W allows us to do is determine the gene frequencies and genotype frequencies within a population at the PRESENT TIME (NOW/ CURRENT) - It may not allow us to accurately predict future since many of these assumptions will not be true. If our predictions are incorrect though we can think through this list of assumptions and consider what is happening in the population.

So why even have these assumptions? Allow us to figure out how many individuals with certain traits/genotypes we would see in the next generation if all of these things were true. Then we can use that information to say how different our population is from what we would predict is happening, and see for example population size or natural selection is or is not having a large impact on a population What do they say when you Assume things?

Hardy-Weinberg Equilibrium Mathematically, we can represent this as follows: We will let “p” represent the frequency of the _____________ allele in a population Then “q” represent the frequency of the ___________ allele. Then the ALLELES in the entire population can be represented by the expression: _________________ *Note the assumption is basic dominance & that 2 alleles are in control of a given trait

Therefore: --the homozygous dominant individuals in a population can be represented by “______”; --the homozygous recessive individuals in a population can be represented by “______”; --the heterozygous individuals in a population can be represented by “______”   Then the GENOTYPES in the entire population can be represented by the expression: ____________________

Hardy-Weinberg Equilibrium We will always write the percentages as decimals. Where 1 = 100%   So if the dominant allele represents 70% of the population we will write it as p=

Example, assume that each allele ( _p_ & _q_ ) has a frequency of 0 Example, assume that each allele ( _p_ & _q_ ) has a frequency of 0.5 (50%) in a population. If this is the case, then: p = _____ (frequency of the dominant allele) q = _____ (frequency of the recessive allele) p2 = _____ (frequency of homozygous dominants) 2pq = _____ (frequency of heterozygotes)  q2 = _____ (frequency of homozygous recessives)

Get in the Habit of showing your work Get in the Habit of showing your work! Try to work out the other terms before looking at the answers on the next slide.

Example, assume that each allele ( __ & __ ) has a frequency of 0 Example, assume that each allele ( __ & __ ) has a frequency of 0.5 (50%) in a population. If this is the case, then: p = _____ (dominant allele) q = _____ (recessive allele) p2 = _____ (homozygous dominants) 2pq = _____ (heterozygotes)  q2 = _____ (homozygous recessives)

Example, assume that 30% of the population has the recessive phenotype Example, assume that 30% of the population has the recessive phenotype. If this is the case, then: p = _____ (frequency of the dominant allele) q = _____ (frequency of the recessive allele) p2 = _____ (frequency of homozygous dominants) 2pq = _____ (frequency of heterozygotes)  q2 = _____ (frequency of homozygous recessives)

Example, assume that 30% of the population has the recessive phenotype Example, assume that 30% of the population has the recessive phenotype. If this is the case, then: Which piece of information is given to you?

Example, assume that 30% of the population has the recessive phenotype Example, assume that 30% of the population has the recessive phenotype. If this is the case, then: Which piece of information is given to you? Recessive phenotype only caused by homozygous recessive genotype (q2) is given

Example, assume that 30% of the population has the recessive phenotype Example, assume that 30% of the population has the recessive phenotype. If this is the case, then: p = _____ (frequency of the dominant allele) q = _____ (frequency of the recessive allele) p2 = _____ (frequency of homozygous dominants) 2pq = _____ (frequency of heterozygotes)  q2 = _____ (frequency of homozygous recessives)

Example, assume that 30% of the population has the recessive phenotype Example, assume that 30% of the population has the recessive phenotype. If this is the case, then: p = _____ (dominant allele) q = _____ (recessive allele) p2 = _____ (homoz dominants) 2pq = _____ (heterozygotes)  q2 = _____ (homoz recessives)

Hardy Weinberg Problems Think what term you are given, and then proceed to the mathematical manipulations that will give you the other terms. Use both equations (allele & genotype) to get the terms you need!

Hardy Weinberg advice & common pitfalls   Never start from p2 even if you think that is what you have. Try to find q2 if you are given phenotypes or genotypes First & foremost you need to figure out what term you are given or could get to easily! Unless it says “allele frequency” or “frequency of the ___ allele” they are not giving you p/q they are giving you p2, 2pq, or q2 Phenotype/genotype are p2, 2pq, or q2 You can go anywhere from q2 IF all of the assumptions are met – all frequencies will remain the same even if the population size itself changes

Basic review – write in Notes under POPULATION GENETICS What term would you use for a change in a population? When we say a population changes, what is actually changing? what are some possible mechanisms of that change?

Questions? Problem Set #1 linked on todays site NOTE new page for individual/population genetics Don’t have to re-write problem DO write out work!

3-weeks until the AP TEST! Make sure you ask questions! Getting behind is not an option at this point – don’t do it – don’t delay doing your work! Review ANY TIME before or after school this week with the exception of TUESDAY morning!

Chipping sparrow