Lecture 1 - Introduction and Mendelian Genetics PDF

Welcome to Genetics Discussion! Genetics in everyday life Agriculture  selecting for ideal crop traits (pest- resistance) Forensics  DNA sample analysis to identify the culprit Ancestral studies  finding similarities in DNA sequences Genomics  studying a complete set of DNA (all genes included...

Welcome to Genetics Discussion! Genetics in everyday life Agriculture  selecting for ideal crop traits (pest- resistance) Forensics  DNA sample analysis to identify the culprit Ancestral studies  finding similarities in DNA sequences Genomics  studying a complete set of DNA (all genes included!) Population genetics  what traits compose a population of organisms Healthcare  COVID tests and genetic disorders  Genetics in everyday life Cat DNA test (genome sequencing) Breed composition Genetic disorder health screen Oral health screen Trait marker analysis The Breed Results are in… Delilah (2-year-old tabby calico) 39% Broadly Western 22% Maine Coon 9% American Shorthair 5% Siberian 4% Norwegian Forest Cat 1% Himalayan The Breed Results are in… Iris (1-year-old tortie) 20% Maine Coon 16% Broadly Western 12.5% American Shorthair 9% Ragdoll 5.5% Egyptian Mau 5% Norwegian Forest Cat 3% Bengal Mendelian Genetics Central Dogma DNA – “Blueprint for life”. Molecule used for storing genetic data. Always exists inside the organism RNA – “Copy of the blueprint”. Intermediate molecule for storing genetic data Only made when needed Protein – String of amino acids Have functionality DNA Structure vs. RNA Structure DNA  deoxyribonucleic acid Pentose sugar  deoxyribose (hydrogen on 2’ carbon) Nitrogenous bases  A, T, G, C (on 1’ carbon) Phosphate group on 5’ carbon RNA  ribonucleic acid Pentose sugar  ribose (hydroxyl group on 2’ carbon) Nitrogenous bases  A, U, G, C (on 1’ carbon) Phosphate group on 5’ carbon Protein Structure Composed of amino acids (20 naturally occurring) Create a polypeptide chain (amino acids strung together) Fold to make a protein Possess a biological function Genes and Chromosomes Gene – sequence of DNA needed to make a protein Locus – gene’s position on the chromosome Insulin - 11p15.5 Chromosome 11 P arm (short arm) Band 15.5  Humans have 2 copies of their genes Diploid = 2 copies of all their DNA Genome – collection of all of an organism’s genes Humans - ~25k protein coding genes E. coli – 4288 protein coding genes Haploid = 1 copy of all their DNA Allele – variant forms of genes (alternative copy) Come from variations in DNA sequence Hair color, eye color, etc. Dominant and Recessive Traits Trait – characteristic of an organism that can be inherited Controlled by genes Simple trait – controlled by 1 gene Complex trait – controlled by many genes Dominant vs. Recessive – depends on how it is inherited Dominant – only requires 1 allele to express trait Recessive – requires 2 copies of the allele to express trait Genotype vs. Phenotype Genotype – genetic makeup/alleles present in an organism(e.g., AA or Aa) Phenotype – the physical traits of an organism (e.g., brown hair or green eyes) Homozygous – both alleles are the same (e.g., AA or aa) Heterozygous – Alleles are different (i.e., Aa) Mendel’s Laws for Inheritance 1st Law (Law of Segregation) – Two members of a gene pair will segregate from each other during gamete formation e.g., Aa alleles will separate into A and a gametes 2nd Law (Law of Independent Assortment) – Members of different gene pairs are transmitted separately A alleles and B alleles don’t depend on each other during segregation AaBb organism will make all combinations of alleles in roughly equal numbers AB, Ab, aB, ab Punnett Square In pea plants, the Y allele determines flower color YY or Yy = yellow flower color (yellow is dominant) yy = white flower color (white is recessive) What happens when we cross two heterozygous (Yy) yellow flowered plants? Y y Genotypic ratio: 1 : 2 : 1 or 25% : 50% : Y Y Yy 25% 1 YY : 2 Yy : 1 yy Phenotypic y Y y yy ratio: 3 : 1 or 75% : 25% 3 yellow : 1 white  Monohybrid and Dihybrid Punnett Squares Monohybrid cross – 2 heterozygous parents (e.g., Aa x Aa) 1:2:1 genotypic ratio (AA:Aa:aa) 3:1 phenotypic ratio (A+:A-) Monohybrid cross – 1 heterozygous parent & 1 homozygous parent (e.g., Aa x aa) 2:2 or 1:1 genotypic ratio (Aa:aa) 2:2 or 1:1 phenotypic ratio (A+:A-) Dihybrid cross – 2 heterozygous parents Genotypic ratio – irrelevant 9:3:3:1 phenotypic ratio (A+B+: A+B-: A-B+: A-B-) Practice Problem (#20) Suppose in dogs, black fur is a dominant trait and caused by allele B. White fur is a recessive trait and caused by allele b. What fur color will a Bb individual have? Practice Problem (#20) 1. If a dog with white fur mates with a heterozygous black dog, what will be the resulting genotypic and phenotypic ratios? Draw a Punnett square to support your answer. 2. If a dog with white fur mates with a homozygous black dog, what fraction of the resulting offspring will be homozygous? Draw a Punnett square to support your answer. Genotypic and Phenotypic Classes For any heterozygous organism: Genotypic classes: 3n Phenotype classes: 2n n = number of segregating gene pairs AaBb 9 genotypes (32) 4 phenotypes (22) Only applies to true dominant- recessive relationship (heterozygous)  Practice Problem (#18) If two heterozygotes whose genes show complete dominance mate, and there is/are: 1 segregating gene pair, there will be ____ genotypic classes and ____ phenotypic classes. 2 segregating gene pairs, there will be ____ genotypic classes and ____ phenotypic classes. 4 segregating gene pairs, there will be ____ genotypic classes and ____ phenotypic classes. Product Rule and Sum Rule Product Rule – probability of events happening simultaneously (AND) You’re picking from a deck of cards (52). What is the probability of picking an ace? What is the probability of picking a heart? What about an ace of hearts? 4/52 = 1/13 , 13/52 = 1/4  Sum rule – probability1/13*1/4 = exclusive of mutually 1/52 events occurring (OR) Probability of rolling a single 6-sided die and rolling a 1 OR a 3 1/6 + 1/6 = 1/3 Practice Problem (#27/28) If a family has 5 children, what is the probability that all 5 will be girls? What is the probability that a future sixth child will be a girl?  Practice Problem (#21/22) Assume that in pea plants yellow and smooth are dominant and unlinked traits. If two heterozygous yellow, smooth plants are mated, what fraction of the offspring can be expected to be simultaneously yellow and wrinkled? In the question above, what is the probability of NOT being yellow and wrinkled?  Practice Problem (#21/22) Two heterozygous yellow, smooth pea plants Flower color  Y or y Yellow is dominant  YY or Yy White is recessive  yy Seed surface  S or s Smooth is dominant  SS or Ss Wrinkled is recessive  ss What are the genotypes and phenotypes of P1 and P2? Practice Problem (#21/22) What fraction of offspring can be expected to be simultaneously yellow and wrinkled? What is the probability of a plant NOT being simultaneously yellow and wrinkled?