AP Biology

Mendel used the scientific approach to identify two laws of inheritance

 Known as the “Father of Genetics”  Experimented with pea plants to develop principles of genetics In the 1800s… before anyone even knew:  what DNA was, let alone how it worked (1940s-1950s)  What meiosis was or how it worked (1870s-1880s)

 Knew some “factor” caused organisms to have “characters” like their parents  Now we call them genes and traits

P generation – true breeding F1 generation – heterozygous F2 generation – 3:1 ratio; recessive trait reappears

1. Dominant: gene that is always expressed if present 2. Recessive: gene that only expressed when 2 copies are inherited 3. Homozygous/True-breeding/Pure: two of the same allele (ex: BB, bb) 4. Heterozygous/Hybrid: two different alleles (ex: Bb) 5. Phenotype: physical appearance of an organism (based on its genes) 6. Genotype: genetic makeup of an organism (letters) 7. P generation: parent generation (Mendel – true-breeding plants) 8. F 1 generation: first generation made from crossing P generation 9. F 2 generation: second generation made from crossing F1generation

 Law of Segregation Two alleles of a gene separate during meiosis Each parent can give one of each homologous chromosome (one copy of each gene) to offspring

 Law of Independent Assortment Each allele pair segregates into gametes independently of other pairs (random) How homologous chromosomes align in metaphase I

 Monohybrid crosses cross 1 trait Ex: pea color F2 generation shows 3:1 ratio

 Dihybrid crosses cross 2 traits at once Ex: pea color and shape F2 generation shows 9:3:3:1 ratio

The laws of probability govern Mendelian inheritance

 Rule of Multiplication Probability that independent events will occur in sequence Look for “and”

 Rule of Addition Probability that events will occur mutually exclusive of each other Look for “or”

 Bozeman Probability in Genetics: Multiplication & Addition Rules Bozeman Probability in Genetics: Multiplication & Addition Rules

Inheritance patterns are often more complex than predicted by simple Mendelian genetics

 Complete dominance (as shown in Mendel’s pea plants) Dominant is always expressed over recessive Recessive only shows if both alleles are recessive RR = purple; Rr = purple; rr = white

 Mendel was lucky – most inheritance follows other patterns…  Let’s look at the exceptions to the norms

 One allele is not completely dominant over another  Heterozygous organisms display a blend between both phenotypes  Example: snapdragons

 Alleles do NOT blend  Both traits show in heterozygous organism Both alleles expressed dominantly Neither allele is recessive  Ex: roan cattle

 Many genes have more than 2 alleles  Examples: human blood type fur color in rabbits

 Multiple genes affect single phenotype  Ex: skin color, height The more dominant alleles inherited, the darker the skin, taller the offspring

 DNA isn’t the only factor that influences a phenotype  Environment can influence genes too  In reality, phenotype is a combination of an organism’s genes, environment, as well as other factors  Examples: Temperature Light Moisture Minerals Nutrients

 Snowshoe hare Genes code for pigments pigments that give its hair a brownish-grey color called agouti. However, during cold winter months the alleles for pigment production are turned-off and the hare appears white in color. In this case temperature regulates the expression of the coat color alleles.

 Himalayan rabbits Genotype ch/ch should produce black pigments in their hair.  when the rabbit’s body temperature is above 37 o C, the ch alleles are turned-off and the rabbit’s hair appears white  if the rabbit’s body temperature falls below 37 o C, black pigments will appear in the rabbit’s hair

 Hydrangeas flower coloration is subject to the pH of the soil in which the hydrangea bush is growing.  In acidic soil, the flowers pink pigments are produced.  In basic soil, blue pigmentation is produced in flowers.

Many human traits follow Mendelian patterns of inheritance

 Analyze inheritance of traits through family relationships

 Autosomal recessive  Defective chloride channels in cells leads to build up of mucus in pancreas, lungs, digestive tract, etc.

 Autosomal recessive  Fatal neurological/brain degeneration beginning at around 6 months of age

 Autosomal recessive  Causes abnormally shaped red blood cells, leads to anemia, clots

 Autosomal dominant  Dwarfism

 Autosomal dominant  Progressive degeneration of brain/nervous system  Late onset (age 35-45)

 Fetal testing Amniocentesis Chorionic villus sampling Blood testing  Newborn screening Blood analysis for genetic disorders