Genetics and Evolution

1. Genetics and Evolution Definitions and concepts from BIOL 102 Lab Manual and Biology by Campbell and Reece, 7th Ed.

2. Genetics! • Founder – Gregor Mendel • Created the laws of Mendelian inheritance in the 1800s • Studied pea plants in a monastery • Law of Segregation • Individual organisms possess a pair of genes for each trait that is randomly passed to offspring • These offspring then have their own pair of genes which is expressed based on dominance • Law of Independent Assortment • Genes for different traits are passed independently to offspring • Did not know at the time that some genes are linked

3. Biodiversity Classification Levels • Genes • Discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA • Chromosomes • Strands of DNA tightly coiled around proteins (histones) that carry genes • Functions in the transmission of hereditary information from parent to offspring • Look at pages 56 and 57 in the lab manual • How many pairs of chromosomes in humans? • Locus (Loci) • The location of a gene on a chromosome • Alleles • Alternative versions (variants) of a gene that produce distinguishable phenotypic effects

4. Phenotype vs. Genotype • Genotype • Alleles an individual has for a genetically controlled locus • Each individual has 2 alleles (1 from each parent) at a particular locus • Capital indicates dominant, lowercase indicates recessive • Phenotype • Physical traits including anything that can be observed or measured empirically in an individual Bb; BB - Heterozygous or Homozygous dominant - Eyes not blue bb - Homozygous recessive - Blue eyes http://naturalsciences.sdsu.edu/ta/classes/lab2.4/trait.jpg

5. Gene Terms • Gene pool • Total aggregate of genes in a population at a time • Homozygous • Having two identical alleles for a given gene • Heterozygous • Having two different alleles for a given gene • Dominant • Allele that is fully expressed in the phenotype of a heterozygote • Recessive • Allele whose phenotypic effect is not observed in a heterozygote

6. Genes and the Environment • Which traits are controlled by genetics? • Which traits are controlled by the environment? • Is there an interaction between genes and the environment? Hemoglobin Eye Color 3 Interacting Alleles Pigment Color Blue or Not Blue Height Weight Range controlled by genetics Amount controlled by environment

7. Genetics • Monogenetic • One gene controls the expression of one trait • Epistasis • Gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited • e.g. eyecolor • Pleiotropy • The ability of a single gene to have multiple effects • e.g. sickle cell anemia

8. Examples of Genetically-Controlled Traits (many are presumed to be monogenetic) – No Maury/Springer! • Hitchhiker’s thumb • Widow’s peak • Pinky bend • Tongue rolling • Cleft chin • Eye color (example of epistasis) • Sickle cell trait/anemia (example of pleiotropy)

9. Exercise • Shake your hands out and clasp your hands with fingers interlaced. Which thumb is on top? • Do it again. Which thumb is on top? • How many are right? • How many are left? • Where does this come from?

10. Punnett Squares • Diagrams used to predict the likelihood of inheritance of certain traits • Named after geneticist Reginald Punnett • 1910 - Co-founder of the Journal of Genetics • Wrote Mendelism – One of the first public books discussing genetics • Mendelian Punnett Square • Pea colors

11. Lethal Genes • Lethal White in Horses • Being homozygous recessive is lethal • Manx Cats • Being homozygous dominant is lethal • Homozygous recessive cats tend to have a full tail

12. Evolution • Evolution • A change in allele frequency in a population over time • Mechanisms of evolution • Mutations • Gene flow • Genetic drift • Non-random mating • Natural selection

13. Mutations • Occur when a base pair or multiple base pairs in the DNA sequence are changed • The ultimate source of all genetic variation • Must occur in the germ-line or sex cells of the organism in order for a mutation to be manifested within a population

14. Types of Mutations

15. Gene Flow (Migration) • The movement of alleles between populations due to immigration/emigration http://evolution.berkeley.edu/evosite/evo101/images/geneflow_beetles.gif

16. Genetic Drift • Caused by change or random variation in the survival and/or reproductive success of individuals -- changes allele frequency • The Founder Effect • when a few individuals inhabit or colonize a new area • this small group represents a subset of the alleles from the original population http://evolution.berkeley.edu/evosite/evo101/images/beetles_mech3.gif

17. Non-Random Mating • Change in the allele frequency in a population due to mate-choice or sexual selection • Preference of a certain phenotype in mates can lead to a higher representation in the final than original population http://www.dwm.ks.edu.tw/bio/activelearner/18/images/ch18c2.jpg

18. http://www.scienceteacherprogram.org/biology/NaturalSelectionIllustration.gifhttp://www.scienceteacherprogram.org/biology/NaturalSelectionIllustration.gif http://evolution.berkeley.edu/evosite/misconceps/images/misconceptions_beavers.gif Natural Selection • Due to varying reproductive success and survival of individuals with a particular phenotype compared to individuals with other phenotypes • Occurs at the individual level

19. Hardy-Weinberg Law • Method for calculating the allele frequency of a specific gene within a population • Establishes the allele frequency within a population at a specific point in time • Must calculate for later generations and compared over time to determine if a population is in EQUILIBRIUM

20. Hardy-Weinberg Equilibrium • Assumptions • No mutations affect that allele frequency • There is no gene flow into or out of the population • There is no genetic drift where random events outside of a population could cause a shift in allele frequency • Individuals mate at random • There are no selective pressures on that trait • NONE OF THE MECHANISMS OF EVOLUTION ARE IN EFFECT

21. Hardy-Weinberg Equilibrium Equation • For a gene with only 2 alleles: • p + q = 1 • p = the frequency of the dominant allele • q = the frequency of the recessive allele • p2 + 2pq + q2 = 1 • p2 = the proportion of homozygous dominantindividuals • q2= the proportion of homozygous recessiveindividuals • 2pq = the proportion of heterozygousindividuals

22. Time to practice calculations using the Hardy-Weinberg Equilibrium equation and Kitties!!!

23. Kitty Genetics • Class in 4 groups • Pull up petfinder.com and search kitties! • Group 1: New York, NY • Group 2: San Francisco, CA • Group 3: Columbia, SC • Group 4: Miami, FL • Look at the first 10 cats that have pictures available and write down which trait out of each of the four fur categories fits for each cat

24. Kitty Monogenetic Traits • Long/Short Hair • LL – Short Hair • Ll – Short Hair • ll – Long Hair • White Fur • WW – White Fur • Ww – White Fur • ww – Some Colored Fur • Spots or Not • SS – Some Spots • Ss – Some Spots • ss – All One Color • Dense Pigment • PP – Black, Brown, or Orange • Pp – Black, Brown, or Orange • pp – Gray, Light Brown, Cream, or White