Mendelian Genetics & Simple Inhertiance

So Who’s Mendel? An Austrian monk named Gregor Mendel. Mendel spent his time breeding pea plants. As he did this over & over & over again, he noticed a patterns to the inheritance of traits from one set of pea plants to the next. By carefully analyzing his pea plant numbers, he discovered three laws of inheritance. Mendel's Laws are as follows: 1. Law of Dominance 2. Law of Segregation 3. Law of Independent AssortmentLaw of DominanceLaw of SegregationLaw of Independent Assortment

Genetic vocabulary… Genotype: the genes of an organism ( all your genes) Phenotype: an organism’s traits (expression of your genes) Allele: variations of a gene Represented with letters for the different types of alleles (PP, Pp, pp) Homozygous: pair of identical alleles for a character (PP, pp) Heterozygous: two different alleles for a gene (Pp) Terminology

Dominant & Recessive Genotypes and Phenotypes ___ Genotypes Recessive genotype: Both recessive alleles must be present (rr). Dominant genotype: At least one dominant allele is present (R-). Character: Tongue Rolling Being able to roll your tongue is a dominant phenotype. Man pictured to the right: Being able to roll your tongue is the dominant trait (phenotype). What would be the dominant genotype? Woman pictured to the right: Not being able to roll your tongue is the recessive (phenotype). What would be the recessive genotype? So what is the baby’s genotype? ___

Mendel's Laws are as follows: 1. Law of Dominance Dominant traits show in the phenotypeLaw of Dominance 2. Law of Segregation Alleles separate during Meiosis and are combine to new alleles at fertilizationLaw of Segregation 3. Law of Independent AssortmentLaw of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. Mendel’s Laws

Working out Mendelian Genetics A Punnett square is a tool for figuring out what the possible genotypes of offspring will be. Lets do a Punnett square for the trait of bent little finger (dominant genotype): David (the Daddy): dominant phenotype [bent finger] What is Davids gentoype? _______ Tami (the Mama): Recessive phenotype [straight finger] What is my genotype? _____ Leo (the Baby): Dominant phenotype [bent finger] What is Leo’s genotype? _______ “Bent Little Finger” (B - ) courtesy of David and Leo Port David’s Genotype: Tami’s Genotype: Punnett Square

So far, we’ve discussed Simple Inheritance & Punnett Squares… But, of course, genetic is much more complicated than that.

“Degrees” of Dominance Incomplete dominance: F1 generation’s appearance between the phenotypes of the 2 parents. Ex: snapdragons Incomplete Dominance

Multiple alleles: more than 2 possible alleles for a gene. Ex: human blood types (ABO) Codominance: two alleles affect the phenotype in separate, distinguishable ways. Ex: AB Blood Type Codominance

Independent Assortment Exercise p.2 Only one of each pair is eventually sorted into each egg or sperm. Procedure: OBJECTIVE: In each of the examples, determine how many different kinds of gametes may be formed from the diploid parent cells. ALLELES: The letters within the parent cells represent genes for a particular trait. The capital letters A, B, D represent alleles for dominant traits. While lower case letters a, b, d represent alleles for recessive traits. WHAT YOU NEED TO DO: - Fill in the gamete cells with the letter or letters which represent all the possible hereditary combinations. - Assume that each pair of genes is located on a different pair of homologous chromosomes (independent assortment). Genetics and Health Science Worksheet

Monohybrid Cross Parental Generation p. 3 Mendel determined that, in pea plants, tall height (T) is dominant to dwarf (t). This means that heterozygous plants (Tt) are tall. The allele for tall (T) completely masks the allele for dwarf (t) in producing the phenotype. This allele relationship is called COMPLETE DOMINANCE. You can use a PUNNETT SQUARE to predict the outcome of crossing a homozygous tall plant (TT) with a dwarf plant (tt). The resulting offspring are called the F1 generation. Cross the two parents, homozygous dominant tall plant (TT) and recessive dwarf plant (tt). Parent (TT) Parent (tt) F1 Generation Note: Always put the dominant allele (T) first when writing a genotype (Example - Tt) What is the expected genotype of the F1 generation? ______________ Describe the expected phenotype(s) of the F1 generation: ___________ Genetics and Health Science Worksheet

Monohybrid Cross F2 Generation p. 4 Cross two members of the F1 generation: Parent (Tt) F2 Generation What is the expected genotype ratio of the F2 generation? ________ What is the expected phenotype ratio of the F2 generation: ________ Genetics and Health Science Worksheet

Incomplete Dominance Parental Generation p. 4 Sometimes, a cross between two individuals, each pure for a particular characteristic, results in partial expression of both traits in the F1 phenotype. One gene incompletely masks the other in the heterozygote. Complete the following Punnett squares using the information. Since dominance is not operating, a slight modification of gene symbols is used. We will use the letter C to represent color in snapdragons. CR will represent the allele for red color and CW will represent the allele for white color. The hybrid of a red and a white snapdragon is pink, so would be represented as CR CW. Use this Punnett square to reveal the genotype of the F1 generation, where the parent plants consist of a red and a white snapdragon plant. Parent (C R C R ) Parent (C W C W ) F1 Generation What is the expected genotype of the F1 generation? ______________ Describe the expected phenotype(s) of the F1 generation: ___________ Genetics and Health Science Worksheet

Incomplete Dominance Parental Generation F2 p. 5 Next, cross two of these F1 snapdragon plants to obtain the theoretical or expected phenotypic and genotypic rations of the F2 generation. Parent (C R C W ) Parent (C W C R ) F2 Generation What is the expected genotype of the F2 generation? ______________ Describe the expected phenotype(s) of the F2 generation: ___________ Genetics and Health Science Worksheet

Probability: The likelihood of occurrence of a given event. p.6 In humans, the fusion of gametes at fertilization results in 46 chromosomes for the developing fetus. Twenty two of those are homologous autosomes plus the sex chromosomes that determine the sex of the offspring. The mother can only contribute an X chromosome. The father can contribute an X or a Y, depending on which was independently assorted to the particular sperm that fertilized the egg. Father (XY) Mother (XX) Sex Chromosomes of Offspring What’s the probability of any sperm cell containing a Y-chromosome? _______ An X-chromosome? ______ What is the probability of fertilization resulting in a female child? _____________ Genetics and Health Science Worksheet

Accuracy of Actual Ratio p.6 In the table below, record data concerning the number of males and number of females in your family. Then record the same data for the entire class. Your instructor will facilitate the gathering of these data.) # Males # Females Ratio Your natal family (you and your siblings) >>>>> Class members’ natal families >>>>>>>>>>>>>>>>>> Is the ratio in your family the same the expected ratio? _________________ Is the ratio for the whole class closer to the expected ratio than was the ratio for your family? __________ Why do you think this is?________________________________________ Genetics and Health Science Worksheet