A. How Common is Genetic Variation? B. Variation and Gene Pools Section Outline Section 16-1 16–1 Genes and Variation A. How Common is Genetic Variation? B. Variation and Gene Pools C. Sources of Genetic Variation 1. Mutations 2. Gene Shuffling D. Single-Gene and Polygenic Traits

16-1 Genes and Variation Variation and Gene Pools A _________ consists of all the genes present in a population, including all the different ______. The _______ ________ is the number of times an allele occurs in the gene pool compared to the occurrence of other alleles in the gene pool. alleles relative frequency

Figure 16–2 Relative Frequencies of Alleles Section 16-1 It’s pretty easy to count up the phenotype. Just count the black mice and the brown mice… Sample Population 48% heterozygous black 36% homozygous brown 16% homozygous black Frequency of Alleles allele for brown fur allele for black fur …but since the homozygous dominant and the heterozygous genotypes share the same phenotype, it’s hard to know the frequency of the genotypes, and the alleles. That’s where Hardy & Weinberg come in…

Who? Hardy & Weinberg Godfrey Hardy Wilhelm Weinberg 1877-1947 1862-1937 They developed an equation that predicted the relative frequency of alleles in a population based on the frequency of the phenotypes in a population, which are a lot easier to count…

Gene Frequency & the Hardy-Weinberg Equation p2 + 2pq + q2 = 1 p2 = the frequency of homozygous dominant genotype 2pq = the frequency of heterozygous genotype q2 = the frequency of homozygous recessive genotype

Hardy-Weinberg & the Frequency of Albinism ________ is a rare _________ trait in humans and other animals. In humans, only 1 in 20,000 people demonstrate the trait. To be an ______, a person has to have a __________ _________ genotype, or __. Albinism recessive albino homozygous recessive aa

Hardy-Weinberg & the Frequency of Albinism According to the _____-________ equation, __ = the frequency of the homozygous recessive genotype, which in the case of albinism is _______, or _______. If __ = _______, then _ = _______, or ______. Hardy Weinberg q2 1/20,000 0.00005 q2 0.00005 q √0.00005 0.00707

Hardy-Weinberg & the Frequency of Albinism If _ = ______, and _ + _ = _, or _____, then _ = _______. (Remember, q = the frequency of a, and p = the frequency of A, A + a = 100%) So about _____ of all the alleles in the population are _, and only about ____ of the alleles in the population are _. q 0.00707 q p 1 100% p 0.99293 99.3% A 0.7% a

Hardy-Weinberg & the Frequency of Albinism Finally, if __ + ___ + __ = _, and _ = _______, and _ = _______, then __ = __________________________ _______________ = __________ = _______, and ___ = _____________ ______________________ = ________________ = _______, and p2 2pq q2 1 q 0.00707 p 0.99293 the frequency of the homozygous p2 dominant genotype (0.99293)2 0.98591 2pq the frequency of the heterozygous genotype 2(0.99293)(0.00707) 0.01404

Hardy-Weinberg & the Frequency of Albinism __ = = ________________ __________________________ = _________ = _______. In albinism then, _____ of the population is __________________, ____ of the population is ____________, and _____ of the population is __________ ________. the frequency of the homozygous recessive genotype (0.00707)2 0.00005 98.6% homozygous dominant 1.4% heterozygous .005% homozygous recessive

Relative Frequencies of Alleles Sample Population 48% heterozygous black 36% homozygous brown 16% homozygous black Frequency of Alleles allele for brown fur allele for black fur

Relative Frequencies of Alleles 16% Homozygous 48% Heterozygous 36% Homozygous Black Mice Black Mice Brown Mice BB BB BB BB Bb Bb Bb Bb Bb Bb bb bb bb bb bb bb BB BB BB BB Bb Bb Bb Bb Bb Bb bb bb bb bb bb bb BB BB BB BB Bb Bb Bb Bb Bb Bb bb bb bb bb bb bb Bb Bb Bb Bb Bb Bb bb bb bb bb bb bb Bb Bb Bb Bb Bb Bb ________________ ________________ ________________ 32 B’s 48 B’s, 48 b’s 72 b’s 80/200 x 100 = 40% B 120/200 x 100 = 60% b 32 + 48 = 80 B’s 48 + 72 = 120 b’s 80 + 120 = 200 B’s & b’s REMEMBER THESE TWO NUMBERS! LET’S SEE IF HARDY & WEINBERG GET THE SAME ANSWERS.

Hardy-Weinberg & the Frequency of Coat Color in Mice If __ + ___ + __ = _, and __ = ___ _______________________________ ________, then __ = ___ or ____, and ___ = _______________________ ____________, = ____, or ____, and __ = __________________________ ________________ = ____,or ____. p2 2pq q2 1 the p2 frequency of the homozygous dominant genotype p2 16% 0.16 2pq the frequency of the hetero- gous genotype 48% 0.48 q2 the frequency of the homozygous recessive genotype 36% 0.36

Hardy-Weinberg & the Frequency of Coat Color in Mice If __ = ____, then _ = _____ = ____ and if __ = ____, then _ = _____ = ____. __________ are easy to observe and count. The Hardy-Weinberg equation allows us to go from the __________ to the frequency of the _____ that cause them. p2 0.16 p √0.16 0.40 q2 0.36 q √0.36 0.60 Phenotypes phenotypes alleles

Hardy-Weinberg & the Frequency of Coat Color in Mice Any change in the relative frequency of alleles in a population is ________. evolution

Sources of Genetic Variation A ________ is any change in a a sequence of ____, due to mistakes the nucleus makes in _________ or due to exposure to ________ or ________ in the environment. Most ________ are _____, but some cause changes in the ____ that affect an organism’s ______. mutation DNA replication radiation chemicals mutations lethal DNA fitness

____________________ during __________ of _______ is a lot like Gene Shuffling ____________________ during __________ of _______ is a lot like shuffling a deck of cards. There is always 52 cards, and the _________ of you being dealt any one card is always the same. Independent assortment Anaphase I meiosis probability

During ____________________, there are 23 ___________ “cards” that Gene Shuffling During ____________________, there are 23 ___________ “cards” that can be “shuffled” and “dealt” in _________ combinations! Also, sometimes the “cards” you are dealt are brand-new and unique due to ___________. independent assortment chromosome 8.4 million crossing over

Monogenic vs. Polygenic Traits The more _____ that control a trait, the more __________ are possible. A widow’s peak is controlled by ___ gene with ___ alleles. Possible _________ include ___, ___, and ___, with widow’s peak being ________. There are ___ __________. You either have one, or you don’t. genes phenotypes one two genotypes WW Ww ww dominant two phenotypes

Figure 16–3 Phenotypes for Single-Gene Trait Section 16-1 Challenge: If 36% of the human population have a widow’s peak, and 64% don’t have a widow’s peak, what is the relative frequency of the recessive allele, w, and the dominant allele W, according to Hardy-Weinberg? What percentage are heterozygous? 100 80 60 40 20 Answer Frequency of Phenotype (%) p2 + 2pq + q2 = 1 q2 = 64% = 0.64 ww q = √.64 = 0.80 = 80% q + p = 1 p = 0.20 = 20% W 2pq = 0.32 = 32% Ww Widow’s peak No widow’s peak Phenotype

Monogenic vs. Polygenic Traits _____________ are controlled by ___ or ____ genes. Human height is controlled by _____ genes and ___ alleles. There are _____ possible __________. The _______________ shows that once again nature seems to favor ______, because it produces the most ______. Polygenic traits two more three six seven phenotypes normal distribution medium variety

Generic Bell Curve for Polygenic Trait Section 16-1 HhGgTt HhGgtt HHGgTt Hhggtt HHGGTt hhggtt HHGGTT Frequency of Phenotype Phenotype (height)