Mendel and Heredity

Father of genetics: Mendel Choose to use pea plants: 1.Two clearly different forms (traits) 2.Male and female parts of the plant in same flower 3.Grows easily, small, matures quickly, and produces many offspring 7 traits observable in pea plants -Flower color (purple or white) -Seed color (yellow or green) -Seed shape (smooth or wrinkled) -Pod color (green or yellow) -Pod shape (smooth or wrinkled) -Flower position (terminal or axial) -Plant height (tall or short)

Expressed traits. Monohybrid cross (cross that involves one pair of contrasting traits). Step 1 Allowed peas to self pollinate for several generations Ensured true breeding (all offspring would display only one trait, pure bloods) P generation, or parent generation, will be first pair crossed in expirement Step 2 Cross pollinated 2 P generation plants with contrasting traits (tall and short) Offspring are called the F1 generation (or first filial generation) He then recorded the number of offspring with each trait Step 3 He allowed the F1’s to self pollinate, called the F2 generation (or 2 nd filial generation) Each offspring was counted

The results F1 plants showed only one form of the trait (all tall, and no short plants) However in the F2’s the trait showed up again (both tall and short plants) He found that the ratio of tall to short was about 3:1 He repeated with all 7 traits and found the same ratio occurred for all of them.

Mendel's Theory 1.For each inherited trait, an individual has two copies (one from each parent) 2.There are alternative versions of a gene (i.e. tall and short) We call these alleles today. 3.When there are two alleles, one can be completely expressed while the other may not be 1.Dominate: the expressed form of the trait 2.Recessive: not expressed when the dominate is present 4.When gametes are formed, alleles for each gene, separate independently of each other, thus gametes only carry one allele for each trait, each gamete contributes during fertilization.

Mendel's findings in modern terms: -Dominate alleles are indicated with upper case letters, i.e. tall is T -Recessive alleles are indicated with lower case letters, i.e. short is t -We always try and use the dominate trait for our letter, T for tall, P for purple, S for smooth, which are all dominate. -Homozygous, the two alleles are the same, i.e. TT or tt or PP or pp. -Heterozygous, the two alleles are different, i.e. Tt or Pp or Ss -THE ONLY TIME THE RECESSIVE CAN BE SEEN IS IF BOTH ARE LOWER CASE, i.e. ss or tt or pp -Genotype (letters) the set of alleles an individual has for a trait. i.e. TT or Tt or Pp -Phenotype (description) or the physical appearance for the trait. i.e. Tall or Short or Purple

Laws of Heredity The law of segregation The two alleles for a character segregate (separate) when gametes are formed. The law of independent assortment The alleles of different genes separate independently of one another during gamete formation. In other words, height alleles separate independently from flower color alleles.

Punnett squares A way of demonstrating the possible outcomes for the combination of gametes. Predicting all possible outcomes from the combination of the gametes. Monohybrid: on set of traits Dihybrid: two traits Trihybrid: three traits…etc…. Test cross is used to determine an unknown genotype

Probability -The likelihood that an event may occur. -We can use probability in genetics, the formula is: -Probability: # of 1 kind of possible outcome/total number of all possible outcomes. -Law of multiplication: used to determine the probability that a combination of two independent events will occur. -Law of addition: the probability that an event can occur in two or more alternative ways is the sum of the separate probabilities of the different way

Pedigree: a family history showing how a trait is inherited over several generations. Sex-linked genes: allele is located on the X or the Y chromosome. Complex Patterns of heredity Polygenic inheritance: several genes influence the phenotype. Incomplete dominance: phenotype is not totally ruled over by dominant trait: red x white = pink Multiple alleles: genes with three or more alleles. Example: Blood types.

Human Blood types (ABO system) -I^A, I^B, and I -A and B represent Carbohydrates that are present, and are both dominant -i has neither, and is recessive. -ii = O See punnett square on this below.

Codominance: both traits are displayed, example: red x white = red and white (not pink like incomplete dom.) Some traits can even be affected by the environment, depending on a stimulus different phenotypes can be visible. For example Hydrangea’s change their flower color based on the pH of the soil. Genetic Disorders (the ones your responsible for on the test) Sickle Cell Anemia: recessive, mutated allele, produces defective hemoglobin, Makes RBC look like a sickle. No known cure. interesting fact, people with sickle cell can’t (almost no chance) get malaria. Cystic Fibrosis: most common fatal hereditary recessive disorder among caucasions. Airways and lungs become clogged with mucus, liver and pancrease become blocked. No known cure.

Hemophilia: recessive genetic disorder, impairs bloods ability to clot, sex linked trait. Huntington’s Disease: dominate, mild forgetfulness, and irritability, eventually causes loss of muscle control, spasms, mental illness, and eventually death. See page 181 for a detail chart on these diseases. Do not do last section: treating genetic disorders.