1. Traits are controlled by particles

Transcription

1 Gregor Mendel: The Father of Genetics Mendelian Genetics Principles of Heredity asics of Heredity: Mendel s Rules 1. Traits are controlled by particles 2. Two genes per trait 3. Heterozygous vs. Homozygous 4. Law of Dominance 5. Law of Segregation 6. Law of Independent ssortment 1. Traits are controlled by particles a. The particles are solids in the cells b. Particles = genes c. Genes are d. Gene means e. lleles are 2. Two genes per trait a. Most biologists thought it was a single gene per trait (in the sperm), but really b. One gene from dad and one from mom c. Trait: general description of what is being controlled by the genes (e.g. seed color) d. Phenotype: visible expression of the genes (e.g. yellow or green) e. Genotype: ctual genes present 3. Heterozygous vs. Homozygous a. the 2 genes may be the same = homozygous e.g. EE or ee (purebred, true, non-carrier) b. or different = heterozygous e.g. Ee (hybrid, crossed, mixed breed, carrier) 1

2 4. Law of Dominance a. when it comes to showing up, some genes are more powerful than others = Dominant e.g. E = or b. Others only show up if both genes are recessive e.g. e = 4. Law of Dominance, cont. c. Some more traits: Polydactyly Syndactyly chondroplasia ntonio lfonseca (P) 4. Law of Dominance, cont. d. Some traits are inherited as Recessives: Sickle-cell anemia Hitchhiker s Thumb lbinism Phenylketylnuria 5. Law of Segregation a. When gametes are made, the two genes for a trait separate and each gamete has only one gene for each trait This happens in meiosis b. Punnett squares: a show the possible offspring from a cross a 6. Law of Independent ssortment a. The way one pair of genes for a trait is inherited has no effect on any other trait b. This allows us to examine multiple traits on a single (larger) Punnett Square. This is called a dihybrid cross and predicts 2 traits at once. c. Probability II The chances of two separate events happening at the same time equals the product of their separate probabilities Parent 1: ab Parent 2: ab 2

3 d. Solving a Dihybrid Cross 1. Make Gamete Tree for both parents 2. Create Punnett Square 3. Insert Gametes along top and side 4. Fill in Punnett Square I. Linkage. genes for two traits carried on the same chromosome. example: Freckles and alleles for red hair Mutations. random changes in the genetic code. may produce unexpected offspring that Mendel couldn t account for. C. Ex: achondroplastic kids (Dd) usually come from two perfectly normal (dd) parents I Polygenic. Controlled by multiple alleles on different chromosomes.. est examined at the population level C. Shown as continuous (bell curve) distribution D. Ex.: human height, skin and hair color. IV. Environmental Effects. some genes are affected by environmental influence. example: RC1 reast Cancer Gene IV. Sex Linkage. traits specifically carried on (usually) the X chromosome. Work like recessive traits (needs 2 alleles to show) C. Show up most often in males (XY versus XX genotype) D. Examples: Hemophilia and Color lindness V. Codominance. two alleles that express themselves equally in the presence of each other. Example: O blood grouping, Roan cattle VI. Multiple lleles. some traits have more than two possible phenotypes because there are more than just two alleles for the trait. This creates multiple combinations of possibility C. Example: O blood grouping Multiple lleles & Codominance: O lood Groups I. and alleles code for glycoproteins (antigens) on red blood cells which can be detected immunochemically:. mix blood sample with type or type antibodies. look for clumping (agglutination) of RC s O allele carries neither antigen 3

4 O lood Groups - antigen only - antigen only - oth and antigens O - Neither antigen I O Genotypes and Phenotypes Genotype ntigen Phenotype I I I I O I I I I O I I, I O I O Neither O Some Important O Factoids IV. I and I are codominant V. oth I and I are dominant to I O VI. pplications. testing compatibility of blood transfusions. Who can donate to who?. What happens in case of incompatibility?. disproving parentage of a child C. forensic science D. childbirthing (Rhogam and hemolytic disease) Pedigree nalysis I. Introduction to Pedigrees. ackground: What is a Pedigree? diagram that shows appearance of phenotypes for a single trait in a group of related individuals from one generation to the next. Pedigree nalysis Father 1. Mother 2.. Reading a Pedigree: Symbols Males (squares or triangles) Females (circles) Marriage/Mating Offspring and Siblings Shaded or Unshaded Crossed out Generation Labels (Roman) Individual Labels (rabic) irth Order (left to right) Dead Siblings Marriage into family Marriage line Oldest Child I. Youngest Child Daughter 1. Son 2. Daughter 3. 4

5 Pedigree nalysis C. Genotypes in a Recessive Pedigree There are some rules to follow: 1. Shaded people are homozygous recessive. Fill them in as such. 2. Unshaded people are either: Homozygous Dominant OR Heterozygous So ssign one Dominant allele to each person 3. Work one generation at a time to determine the unknown genotypes. NEVER skip generations!!!!! Please copy this pedigree II-1 III-1 II-2 I-1 I-2 II-3 II-4 II-5 III-2 II-6 III-3 Pedigree nalysis, continued dvanced Pedigrees: Unknown Inheritance. First, flip a coin i.e. pick a mode ( Dom or Rec). ssign known genotypes across pedigree C. egin filling in unknowns Remember to work 1 generation at a time!!! Don t skip!!! D. Look for anomalies (matings that don t work) E. Try the pedigree again with the other mode of inheritance F. Use colored pencils, different ink pens, or different letters to help you solve 5