MRS. MACWILLIAMS ACADEMIC BIOLOGY 17.1 Genes and Variation MRS. MACWILLIAMS ACADEMIC BIOLOGY

I. Genetics Joins Evolutionary Theory *1859- Darwin developed his “Theory of Evolution” without knowing how heredity worked *1865- Mendel published his genetic experiments on inheritance in pea plants 1900’s- genetic theory sky rocketed Genotype and Phenotype in Evolution Genetic variation if the raw material for natural selection Molecular genetics helps us understand how evolution works

Gene- a sequence of DNA that codes for a protein and determines a trait, a specific characteristic of an individual *Allele- specific forms of a gene Ex. GENES= eye color ALLELES= genes for blue eyes, brown eyes, etc. Heritable traits are controlled by genes Changes in a gene or chromosome, a structure of DNA + protein that contains genetic information, generate variation You contain two sets of genes, one set from mom and one set from dad genotype- genetic makeup of an organism ex. Bb (B and b are genes for eye color) phenotype- physical characteristics of an organism ex. Blue eyes genotype + environment creates the phenotype

Natural selection acts directly on PHENOTYPE *It is the ORGANISM that survives or dies, not a single gene Some individuals have phenotypes that are better suited to their environment than others = produce more offspring, pass on more copies of their genes to next generation.

B. Population and Gene Pools population- group of individuals of the same species that mate and produce offspring gene pool- all the genes that are present in a population allele frequency- number of times an allele occurs in a gene pool, compared to the total number of ALLELES in the pool for the same GENE ALLELE FREQUENCY???

LET’S TRY A CLASSROOM EXAMPLE! # students with blue eyes # students with brown/green/hazel eyes Total number of students WHAT IS THE ALLELE FREQUENCY FOR BLUE EYES? blue eyes/total # of students = (___%) WHAT IS THE ALLELE FREQUENCY FOR NON-BLUE EYES? non-blue eyes/total # of students = (___%)

Evolution, in genetic terms, involves the change in frequency of alleles in a population over time! Natural selection operates on individuals, but resulting changes in allele frequencies show up in populations Populations evolve, individuals do not!

II Sources of Genetic Variation Mutations- change in genetic material of a cell Changes in phenotype may or may not affect fitness Some may be lethal or may lower fitness; others may be beneficial  Mutations matter in evolution only if they can be passed from generation to generation mutation must occur in either eggs or sperm Research suggests each of us is born with roughly 300 mutations that make some of our DNA different from our parents – most are neutral NOTE: Mutations matter ONLY if they can be passed to the next generation

Genetic recombination in Sexual Reproduction Mutations are not primarily why you look different than other people (even parents and siblings) During creation of eggs and sperm, genes recombine increasing new genotypes in each generation *You will learn more about when we talk about MEIOSIS

Ex. bacteria can swap genes with other bacteria Lateral gene transfer a. organisms pass genes from one individual to another that is NOT its offspring Ex. bacteria can swap genes with other bacteria can occur between organisms of the same or different species increases genetic variation in a species that picks up the “new” genes Lateral gene transfer to another species

III. Single Gene and Polygenic Traits single-gene trait- trait controlled by only ONE gene may have just two or three distinct phenotypes Ex. red or white flower genes The most common form of the allele can be dominant or recessive a dominant allele produces a dominant phenotype in individuals who have ONE copy of the allele, which can come from just one parent (Red flowers; RR or Rr) a recessive allele to produce a recessive phenotype, the individual must have TWO copies, one from each parent (white flowers; rr) NOTE: Dominance of an allele does not necessarily mean that the dominant phenotype will always appear with greater frequency in a given population

Polygenic trait- trait controlled by TWO OR MORE genes Each gene of a polygenic trait often has two or more alleles A single polygenic trait often has many possible genotypes and even more different phenotypes Example is HUMAN HEIGHT! In the US, the average heights are: Males ~5’10.5” Females ~5’5” But we have a huge variation!

IV. Alleles and Fitness Lethal Alleles- cause an organism to die only when present in homozygous condition Examples (2 recessive alleles) cystic fibrosis (cardiorespiratory disorder) and sickle cell anemia (blood disorder) Ex. (2 dominant alleles) Huntington’s disease a degenerative brain disorder Negative Impact of Low Allele Frequency loss of genetic diversity an increase in inbreeding lack of adaptation to changing environmental conditions population extinction