Genetics & Heredity December 16th/17th, 2008

Warm Up Are Traits Inherited? Procedure: Look at your classmates. Note how they vary in the shape of their front hairline, the space between their front teeth, the way in which their earlobes are attached, eye color, and anything else you can come up with. Make a list of the different forms of these traits that you have observed in the class or among other people you know. Think About It: Inferring: Could these traits be inherited? From whom could they be inherited? Inferring: How is it possible that these traits could be found in a person and his or her biological grandparents, but not in the biological parents?

Gregor Mendel’s Crosses Gregor Mendel was an Augustinian Monk. In 1857 he began breeding and cross breeding pea plants. He observed properties of the plants such as seed color and shape, as well as flower color. Nothing was known about genes or DNA at the time. His results yielded the following two laws:

Law of Segregation- The random assortment of either pair of homologous chromosomes to opposite poles during Meiosis I. Creates different gametes.

Law of Independent Assortment- The movement of one pair of chromosomes does not affect the movement of another pair. They segregate independently.

Key Genetic Terms Genetics – is the scientific study of heredity. Trait – a specific characteristic, such as seed color or plant height, that varies from one individual to another. Hybrids – offspring that are crosses between parents with different traits.

Key Genetic Terms Gene- a section of DNA on a chromosome that codes for a particular trait. ex. hair color.

Key Genetic Terms Allele- one of several forms of a gene. ex. brown or black Locus- location of a gene on a chromosome. ex. brown hair color at the top of chromosome 19

Key Genetic Terms Dominant Allele- the form of the gene that is expressed even in the presence of the alternative form. Uses a capital letter. (B= Brown hair color) Recessive Allele- the form of a gene that is expressed only when it is alone or paired with another recessive. Uses a lower case letter. (b= blond hair color

Key Genetic Terms Homozygous- having two of the same type of alleles. Ex. BB (homozygous dominant) or bb (homozygous recessive). Heterozygous- having two different types of alleles. Ex. Bb

Key Genetic Terms Phenotype- the physical expression shown based on the genetic makeup. Ex. Brown hair Genotype- the actual genetic makeup of the individual. Ex. Bb (confers phenotype)

Probability Probability – The likelihood that a particular event will occur. ex. flipping a coin and it coming up heads What is the probability of this happening? “1 out of 2” or “1/2” or “50%” or “.5” If you flip a coin three times in a row, what is the probability of it coming up heads every time?

Probability cont’d Well, because each coin flip is “independent” of the last, the probability of each flip is still 1/2. Therefore, the probability that you will flip heads three times in a row is: 1/2 x 1/2 x 1/2 = 1/8 The same principle of probability can be used to predict the outcomes of genetic crosses. Such as the probability of someone having blues eyes as opposed to brown, and so on.

Ratios A ratio is an expression which compares quantities relative to each other. Examples: What is the ratio of boys to girls in this room? What is the ratio of freshmen to sophomores to upper classman in this room?

Key Genetic Terms Punnett Square - A diagram used to determine the possible gene combinations that might result from a genetic cross. Monohybrid Cross - A mating in which just 1 trait is focused on. Ex. Just plant color or just plant height. Letters are used to represent the parent’s genes.

Monohybrid Cross Cross a Homozygous Dominant Purple (PP) flowered plant with a Homozygous recessive White flowered plant (pp). P P p Pp Pp

Gregor Mendel’s Crosses P = Parental Generation Purple x White F1= First Filial Generation All purple F2 = Second Filial Generation 3:1 Purple to white What is dominant? How do we explain?

Monohybrid Cross The offspring have one gene from each parent but only show purple phenotype. Now cross the offspring. P p P PP Pp p Pp pp Heterozygous Purple Flower x Heterozygous Purple Flower

Monohybrid Cross The offspring show a 3 : 1 phenotype distribution. 1 PP Homo. Dom. Purple 2 Pp Hetero. Purple 1 pp Homo. Rec. White Genotype Phenotype P p P PP Pp p Pp pp

Test Cross Used to determine a genotype that is unknown. Ex. A purple flower of unknown genotype with a white pp flower. Predict outcome for each scenario and compare with actual results.

Work Sheet Simple Genetics Cross Practice Problems (The Monohybrid Cross)

Practice Pick one of the traits for a pea plant from the diagram above and create a Punnett Square that shows a possible monohybrid cross. Pick two of the traits for a pea plant from the diagram above and create a Punnett Square that shows a possible dihybrid cross.

Lab #2 Investigating Inherited Traits (a.k.a. Making Babies)

Different Types Of Inheritance Incomplete Dominance- When one trait is NOT completely dominant over the other. A Combined expression is shown. Ex. Snapdragons RR= Red rr= white Rr= pink

Different Types Of Inheritance Co-Dominance- When both of the dominant traits are expressed. A combined expression is shown. Ex. Cows BB= brown WW= white RW= roan (brown and white spots)