Heredity Heredity is the passing of traits from one generation to another, or inheritance.

Inherited Traits vs. Environmental Factors Inherited Traits are those that are passed from parent to offspring Environmental Factors can also have an effect on how you look Diet Exercise Smoking/Drinking Sun exposure

Why do I look like my parents Why do I look like my parents?! You look like your parents because genetic information (DNA) is passed from parent to offspring during sexual reproduction. Each sex cell (egg or sperm) of the parent organism (plant or animal) contains one-half of the genetic material needed to create a new organism.

Who do you look like? Draw a picture of yourself and then label all of the traits that you inherited from someone in your family (write the family member’s name beside that trait) For example, if your hair is red and your mother’s hair is red, write her name beside your hair.

What are Chromosomes? A structure found in the nucleus of a cell that contains the genetic information (DNA). Remember, these are those things you were drawing that doubled and split in Mitosis and Meiosis. Humans have 46 in every cell except sex cells, which have 23.

What Is a Gene? A gene is a segment of DNA found on a chromosome that determines the inheritance of a particular trait. Genes are what make one individual look different from another

Principles of Heredity Each trait is governed by two factors – now called genes. 2. Genes are found in alternative forms called alleles. 3. Some alleles are dominant and mask alleles that are recessive.

Dominant Traits Dominant Trait- a trait that will always be expressed in the phenotype. These alleles are represented by a capital letter. Ex. Having a widow’s peak is dominant to not having a widow’s peak.

Recessive Trait Recessive Trait- a trait that will only be expressed in the phenotype if two recessive alleles are present. In the presence of a dominate trait, the recessive trait will not be expressed. These alleles are represented by lowercase letters. Ex. Hitchhiker’s thumb is recessive to straight thumb.

Seven Traits used by Mendel in Genetic Studies

Genotype and Phenotype Genotype: alleles carried by an individual ex. RR, Rr, rr Phenotype: physical characteristic or appearance of an individual ex. Round, wrinkled

Principles of Heredity Mendel’s Experiment with Peas Round seed x Wrinkled seed RR rr F1: All round seed coats Rr Homozygous Dominant Homozygous Recessive Heterozygous

Homozygous parents can only pass one form of an allele to their offspring. R

Heterozygous parents can pass either of two forms of an allele to their offspring. R r R r

Principles of Heredity Mendel was a scientist studying peas as a way to explore genetics. He needed to explain: Why one trait seemed to disappear in the first generation. 2. Why the same trait reappeared in the second generation in one-fourth of the offspring.

Mendel’s Principle of Genetic Segregation In the formation of gametes, the members of a pair of alleles separate (or segregate) cleanly from each other so that only one member is included in each gamete. Each gamete has an equal probability of containing either member of the allele pair.

Genetic Segregation Parentals: RR x rr F1 x F1: Rr x Rr R R r r

Genetic Segregation Genotypic Ratio: ¼ RR + ½ Rr + ¼ rr Phenotypic Ratio: ¾ Round + ¼ Wrinkled

Mendel’s Principle of Independent Assortment When gametes are formed, the alleles of one gene segregate independently of the alleles of another gene producing equal proportions of all possible gamete types.

Using Probability in Genetic Analysis 1. Probability (P) of an event (E) occurring: P(E) = Number of ways that event E can occur Total number of possible outcomes Eg. P(Rr) from cross Rr x Rr 2 ways to get Rr genotype 4 possible outcomes P(Rr) = 2/4 = 1/2

Phenotypic Ratio of Offspring Sex Determination Female Male XX x XY ½ X ½ X ½ X ½ Y ¼ XX ¼ XX ¼ XY ¼ XY Phenotypic Ratio of Offspring ½ Female + ½ Male

Colorblindness

Pedigree for Colorblindness, an X-linked Recessive Trait