Punnett Square Demonstrates how alleles can be combined when the F1 plants are self-fertilized to produce an F2 generation. Shows that 1/4 of the F2 plants should be homozygous dominant (TT), 1/2 heterozygous (Tt), and the remaining 1/4 to be homozygous recessive (tt).

Genotype The genetic makeup of an individual. Genotype can refer to an organism’s entire genetic makeup or to the alleles at a particular locus. The Genotype of the pea pods here would be either “RR” “Rr” “Rr” or “rr”

Phenotypes The observable or detectable physical characteristics of an organism; the detectable expressions of genotypes, frequently influenced by environment.

Codominance The expression of two alleles in heterozygotes. In this situation, neither allele is dominant or recessive; thus, both influence the phenotype. (AB bloodtype)

Exercise…

Microevolution Small genetic changes that occur within a species. A human example is the variation seen in the different ABO blood types.

Principle of Independent Assortment The distribution of one pair of alleles into gametes does not influence the distribution of another pair. The genes controlling different traits are inherited independently of one another.

Mendelian Traits Characteristics that are influenced by alleles at only one genetic locus. Examples include many blood types, such as ABO. Many genetic disorders, including Achondroplasia (dominant), Huntington disease (dominant), and Sickle-cell anemia (recessive) are also Mendelian traits.

Huntington Disease Huntington disease affects about 1 out of every 100,000 people and is caused by a dominant mutation on chromosome 4. A person with the allele has a 50% chance of passing it their offspring. There is no cure and symptoms most often occur between ages 35 and 45. By this time, most people who want children have had them and may have passed the mutant allele on to their offspring.

Huntington’s Disease… Suppose one of your parents was diagnosed with Huntington disease. Would you be tested to determine whether you carried the allele for the disease? If you have the test, you will either be relieved by the results or know that you’ll develop a neurological disease that will ultimately kill you.

Non-Mendellian traits: Polygenic Inheritance Polygenic traits, or continuous traits, are governed by alleles at two or more loci, and each locus has some influence on the phenotype. Hair, eye and skin color are polygenic traits

Polygenic traits cont…. Stature, shape of face, fingerprint patterns are polygenic traits Most can be measured, i.e. height in feet and inches or meters and centimeters

Mitochondrial Inheritance All cells contain mitochondria that convert energy into a form that can be used by the cell. Each mitochondrion contains copies of a ring-shaped DNA molecule, or chromosome. Animals of both sexes inherit their mtDNA, and all mitochondrial traits, from their mothers. All the variation in mtDNA is caused by mutation, which makes it very useful for studying genetic change over time.

Gene Flow The exchange of genes between populations. If individuals move temporarily and mate in the new population (leaving a genetic contribution), they don’t necessarily stay there. Example: “Sex Tourism”

Genetic Drift In each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals. The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals. That, in a nutshell, is genetic drift. It happens to ALL populations—there’s no avoiding the vagaries of chance. Genetic drift affects the genetic makeup of the population but, unlike natural selection, through an entirely random process. So although genetic drift is a mechanism of evolution, it doesn’t work to produce adaptations.

Founder Effect Occurs when a small band of “founders” leaves its parent group and forms a colony elsewhere. A new population is established and as long as mates are chosen within this population, all the members will be descended from the founders. A once rare allele that was carried by even one of the founders can eventually become common.

Bottleneck Cheetahs, like many other species, have passed through a genetic bottleneck. As a species they have little genetic variation.