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

2. 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

3. 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

4. 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.

5. 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???

6. 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 = (___%)

7. 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!

8. 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

9. 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

10. 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

11. 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

12. 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!

13. 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