1. Classical (Mendelian) Genetics Gregor Mendel

2. Vocabulary Genetics: The scientific study of heredityGenetics: The scientific study of heredity Allele: Alternate forms of a gene/factor.Allele: Alternate forms of a gene/factor. Genotype: combination of alleles an organism has.Genotype: combination of alleles an organism has. Phenotype: How an organism appears.Phenotype: How an organism appears. Dominant: An allele which is expressed (masks the other).Dominant: An allele which is expressed (masks the other). Recessive: An allele which is present but remains unexpressed (masked)Recessive: An allele which is present but remains unexpressed (masked) Homozygous: Both alleles for a trait are the same.Homozygous: Both alleles for a trait are the same. Heterozygous: The organism's alleles for a trait are different.Heterozygous: The organism's alleles for a trait are different.

3. History Principles of genetics were developed in the mid 19th century by Gregor Mendel an Austrian MonkPrinciples of genetics were developed in the mid 19th century by Gregor Mendel an Austrian Monk Developed these principles without ANY scientific equipment - only his mind.Developed these principles without ANY scientific equipment - only his mind. Experimented with pea plants, by crossing various strains and observing the characteristics of their offspring.Experimented with pea plants, by crossing various strains and observing the characteristics of their offspring. Studied the following characteristics:Studied the following characteristics: –Pea color (Green, yellow) –Pea shape (round, wrinkled) –Flower color (purple, white) –Plant height (tall, short) Made the following observations (example given is pea shape)Made the following observations (example given is pea shape) When he crossed a round pea and wrinkled pea, the offspring (F1 gen.) always had round peas.When he crossed a round pea and wrinkled pea, the offspring (F1 gen.) always had round peas. When he crossed these F1 plants, however, he would get offspring which produced round and wrinkled peas in a 3:1 ratio.When he crossed these F1 plants, however, he would get offspring which produced round and wrinkled peas in a 3:1 ratio.

4. Laws of Inheretance Law of Segregation: When gametes (sperm egg etc…) are formed each gamete will receive one allele or the other.Law of Segregation: When gametes (sperm egg etc…) are formed each gamete will receive one allele or the other. Law of independent assortment: Two or more alleles will separate independently of each other when gametes are formedLaw of independent assortment: Two or more alleles will separate independently of each other when gametes are formed

5. Punnett Squares Genetic problems can be easily solved using a tool called a punnett square.Genetic problems can be easily solved using a tool called a punnett square. –Tool for calculating genetic probabilities A punnett square

6. Monohybrid cross (cross with only 1 trait) Problem:Problem: Using this is a several step process, look at the following exampleUsing this is a several step process, look at the following example –Tallness (T) is dominant over shortness (t) in pea plants. A Homozygous tall plant (TT) is crossed with a short plant (tt). What is the genotypic makeup of the offspring? The phenotypic makeup ?

7. Punnet process 1.Determine alleles of each parent, these are given as TT, and tt respectively. 2.Take each possible allele of each parent, separate them, and place each allele either along the top, or along the side of the punnett square.

8. Punnett process continued Lastly, write the letter for each allele across each column or down each row. The resultant mix is the genotype for the offspring. In this case, each offspring has a Tt (heterozygous tall) genotype, and simply a "Tall" phenotype.Lastly, write the letter for each allele across each column or down each row. The resultant mix is the genotype for the offspring. In this case, each offspring has a Tt (heterozygous tall) genotype, and simply a "Tall" phenotype.

9. Punnett process continued Lets take this a step further and cross these F1 offspring (Tt) to see what genotypes and phenotypes we get.Lets take this a step further and cross these F1 offspring (Tt) to see what genotypes and phenotypes we get. Since each parent can contribute a T and a t to the offspring, the punnett square should look like this….Since each parent can contribute a T and a t to the offspring, the punnett square should look like this….

10. Punnett process continued Here we have some more interesting results: First we now have 3 genotypes (TT, Tt, & tt) in a 1:2:1 genotypic ratio. We now have 2 different phenotypes (Tall & short) in a 3:1 Phenotypic ratio. This is the common outcome from such crosses.Here we have some more interesting results: First we now have 3 genotypes (TT, Tt, & tt) in a 1:2:1 genotypic ratio. We now have 2 different phenotypes (Tall & short) in a 3:1 Phenotypic ratio. This is the common outcome from such crosses.

11. Dihybrid crosses Dihybrid crosses are made when phenotypes and genotypes composed of 2 independent alleles are analyzed.Dihybrid crosses are made when phenotypes and genotypes composed of 2 independent alleles are analyzed. Process is very similar to monohybrid crosses.Process is very similar to monohybrid crosses. Example:Example: –2 traits are being analyzed –Plant height (Tt) with tall being dominant to short, –Flower color (Ww) with Purple flowers being dominant to white.

12. Dihybrid cross example The cross with a pure-breeding (homozygous) Tall,Purple plant with a pure-breeding Short, white plant should look like this.The cross with a pure-breeding (homozygous) Tall,Purple plant with a pure-breeding Short, white plant should look like this. F1 generation

13. Dihybrid cross example continued Take the offspring and cross them since they are donating alleles for 2 traits, each parent in the f1 generation can give 4 possible combination of alleles. TW, Tw, tW, or tw. The cross should look like this. (The mathematical “foil” method can often be used here)Take the offspring and cross them since they are donating alleles for 2 traits, each parent in the f1 generation can give 4 possible combination of alleles. TW, Tw, tW, or tw. The cross should look like this. (The mathematical “foil” method can often be used here) F2 Generation

14. Dihybrid cross example continued Note that there is a 9:3:3:1 phenotypic ratio. 9/16 showing both dominant traits, 3/16 & 3/16 showing one of the recessive traits, and 1/16 showing both recessive traits.Note that there is a 9:3:3:1 phenotypic ratio. 9/16 showing both dominant traits, 3/16 & 3/16 showing one of the recessive traits, and 1/16 showing both recessive traits. Also note that this also indicates that these alleles are separating independently of each other. This is evidence of Mendel's Law of independent assortmentAlso note that this also indicates that these alleles are separating independently of each other. This is evidence of Mendel's Law of independent assortment

15. The Importance of the Environment The environmental influences the expression of the genotype so the phenotype is altered. Hydrangea flowers of the same genetic variety range in color from blue- violet to pink, depending on the acidity of the soil. Multifactorial ; many factors, both genetic and environmental, collectively influence phenotype in examples such as skin tanning

16. Chromosome Theory of Inheritance Improved microscopy techniques, understand cell processes and genetic studies converged during the late 1800’s and early 1900’s. It was discovered that Mendelian inheritance has its physical basis in the behavior of chromosomes during sexual life cycles. Walter S. Sutton Theodor Boveri Hugo de Vries

17. Pedigree analysis reveals Mendelian patterns in human inheritance In these family trees, squares symbolize males and circles represent females. A horizontal line connecting a male and female (--) indicates a mating, with offspring listed below in their order of birth, from left to right. Shaded symbols stand for individuals with the trait being traced.

18. Disorders Inherited as Recessive Traits Over a thousand human genetic disorders are known to have Mendelian inheritance patterns. Each of these disorders is inherited as a dominant or recessive trait controlled by a single gene. Most human genetic disorders are recessive. A particular form of deafness is inherited as a recessive trait.

19. Many human disorders follow Mendelian patterns of inheritance Cystic fibrosis, which strikes one out of every 2,500 whites of European descent but is much rarer in other groups. One out of 25 whites (4% ) is a carrier. The normal allele for this gene codes for a membrane protein that functions in chloride ion transport between certain cells and the extracellular fluid. These chloride channels are defective or absent. The result is an abnormally high concentration of extracellular chloride, which causes the mucus that coats certain cells to become thicker and stickier than normal.

20. Tay-Sachs disease is caused by a dysfunctional enzyme that fails to break down brain lipids of a certain class. Is proportionately high incidence of Tay- Sachs disease among Ashkenazic Jews, Jewish people whose ancestors lived in central Europe Sickle-cell disease, which affects one out of 400 African Americans. Sickle-cell disease is caused by the substitution of a single amino acid in the hemoglobin protein of red blood cells

21. Dominantly Inherited Disorders Achondroplasia, a form of dwarfism with an incidence of one case among every 10,000 people. Heterozygous individuals have the dwarf phenotype. Huntington’s disease, a degenerative disease of the nervous system, is caused by a lethal dominant allele that has no obvious phenotypic effect until the individual is about 35 to 45 years old.

22. Sex-Linked Disorders in Humans Duchenne muscular dystrophy, affects about one out of every 3,500 males born in the United States. People with Duchenne muscular dystrophy rarely live past their early 20s. The disease is characterized by a progressive weakening of the muscles and loss of coordination. Researchers have traced the disorder to the absence of a key muscle protein called dystrophin and have tracked the gene for this protein to a specific locus on the X chromosome. Posture changes during progression of Duchenne muscular dystrophy.

23. Hemophilia is a sex-linked recessive trait defined by the absence of one or more of the proteins required for blood clotting.

24. Color Blindness In Humans: An X-Linked Trait Numbers That You Should See If You Are In One Of The Following Four Categories: [Some Letter Choices Show No Visible Numbers] Sex-Linked Traits: 1.Normal Color Vision: A: 29, B: 45, C: --, D: 26 2. Red-Green Color-Blind: A: 70, B: --, C: 5, D: -- 3.Red Color-blind: A: 70, B: --, C: 5, D: 6 4.Green Color-Blind: A: 70, B: --, C: 5, D: 2

25. Pattern Baldness In Humans: A Sex Influenced Trait Baldness is an autosomal trait and is apparently influenced by sex hormones after people reach 30 years of age or older. In men the gene is dominant, while in women it is recessive. A man needs only one allele (B) for the baldness trait to be expressed, while a bald woman must be homozygous for the trait (BB). What are the probabilities for the children for a bald man and woman with no history of baldness in the family?