A. Heredity: The passing of traits (characters) from parents to offspring B. Genetics: The branch of biology that studies heredity. 1. Gregor Mendel: “father of genetics

C. Mendel’s Peas: 1. had many traits that were easy to identify, and these traits existed in two very different forms (page 310). 2. mating is easy to control a. male and female parts are found in the same flower b. were able to self fertilize 3. small, grow rapidly, mature quickly, and produce many offspring.

D. Mendel’s Experiment 1. Mendel performed monohybrid crosses (crosses that involve one pair of contrasting traits). a. Ex. Purple and White flower color 2. **A cross is a mating or breeding of two individuals**

3. Mendel made sure his pea plants were true breeding (displayed only one form of a particular trait) 4. He crossed two true breeding plants. This is called the parental, or P Generation. 5. He examined each of the offspring F 1 Generation 6. He allowed the F 1 Generation to self- pollinate and called their offspring the F 2 Generation

E. Mendel’s Results: 1. The F 1 Generation showed only one form of the trait 2. The F 2 Generation showed two forms of the trait, in a ratio of 3 to 1.

Figure 10-3 For each monohybrid cross, Mendel cross-fertilized true- breeding plants that were different in just one character—in this case, flower color. He then allowed the hybrids (the F 1 generation) to self-fertilize.

A. Mendel’s Four Hypothesis: 1. For each inherited character, an individual has two copies of the gene-one from each parent 2. There are alternative versions of genes, called alleles. 3. When two different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance. a.The expressed form is called dominant (capital letter) b.form that is not expressed is called recessive (lowercase letter).

4. When gametes are formed, the alleles for each gene in an individual separate independently of one another. a. Thus, gametes carry only one allele for each trait

B. Homozygous: An individual that has the same alleles for a particular gene. 1. AA (homozygous dominant) 2. aa (homozygous recessive) C. Heterozygous: An individual that has different alleles for a particular gene. 1. Only the dominant allele is expressed. Ex. Aa

D. Genotype: The set of alleles that an individual has E. Phenotype: The physical appearance (expression) of a trait. 1. Ex. A: brown hair & a: blond hair 2. Aa would be an individuals genotype, and brown hair would be the phenotype. 3. Genotypic ratio of a Aa x Aa is 1:2:1 4. Phenotypic ratio of Aa x Aa is 3:1

F. Mendel’s Laws of Heredity: 1. Law of segregation: ◦ The two alleles for a trait separate when gametes are formed 2. Law of independent assortment: ◦ The alleles of different genes separate independently of one another during gamete formation.

G. Probability: the likelihood that a specific event will occur H. Punnett square: A diagram that predicts the expected outcome of a genetic cross by considering all possible combinations of gametes in a cross. I. Test cross: A cross in which an individual whose phenotype is dominant, but whose genotype is not known, is crossed with a homozygous recessive individual.

A. Polygenic Trait: A trait that is influenced by several genes. Eye color, height, weight, hair color, and skin color are all polygenic traits. B. Incomplete Dominance: Occurs when an individual displays a trait that is intermediate between two parents. ◦ Ex. A black chicken and white chicken will produce blue chicken offspring

Figure 10-9 In a monohybrid cross where neither parent trait is dominant, the hybrids have an intermediate phenotype. But the parent phenotypes can appear again in the F 2 generation.

C. Codominance: Occurs when both forms of the dominant alleles are expressed at the same time ◦ Ex. Blood Type AB expresses both alleles D. Multiple Alleles: Genes with three or more alleles. Ex: ABO blood groups. E. **Phenotypes can also be influenced by the environment ◦ Sun exposure, temperature, nutrition

F. Chromosome Theory of Inheritance: 1. genes are located on chromosomes 2. the behavior of chromosomes during meiosis and fertilization account for inheritance patterns. G. Alleles for the same gene are found at the same location of the homologous chromosomes called a gene locus. H. Gene linkage: the tendency for alleles on one chromosome to be inherited together. 1. The closer the genes are, the greater the genetic linkage.

I. Sex-Linked trait: A trait whose allele is located on the X chromosome. 1. The trait is usually only seen in males because males only have one X Chromosome. 2. Females are usually carriers of the trait.  Female: XXMale: XY 3. Ex. Male pattern baldness, color blindness, Hemophilia, Muscular Dystrophy