Mendel and the Gene Idea AP Biology Crosby High School

Gregor Mendel Lived as a monk Worked in the garden Carefully bred pea plants and observed results –True-Breeding: Self pollination –Hybridization: P (Parental) Generation F1 (Filial) Generation F2 (Filial) Generation

Observed Traits Back

Mendel’s Methods

Law of Segregation Alternative versions of genes account for variations in inherited traits Organisms inherit 2 alleles for each trait –True-breeding: Identical alleles –Hybrids: Different alleles If alleles are different, Dominant allele is expressed Two alleles for each character segregate during gamete production –Law of Segregation

Useful Vocabulary Homozygous: Contains two identical alleles Heterozygous: Contains two differing alleles Genotype: Genetic makeup Phenotype: Observed traits Test Cross: breeding recessive homozygous with unknown genotype

Punnett Square Predicts the results for a genetic cross between individuals of known gentoype. Monohybrid cross: observes a single trait –Heterozygous -1:2:1 Genotype –Heterozygous – 3:1 Phenotype Dihybrid cross: observes two traits –Heterozygous 9:3:3:1 Phenotype Mendel’s traits Mendel’s traits

Rules of Probability More accurate with larger sample size Rule of Multiplication –Used to solve AND statements –First decide the chance of each individual event –Multiply the chances together Rule of Addition –Used for OR statements –Decide the chance of each event –Add the chances together

Using Probability PpYyRr x Ppyyrr What is the chance of expressing two recessive traits? Multiple possibilities –ppyyRr –ppYyrr –Ppyyrr –PPyyrr –ppyyrr

Types of “Dominance” Complete Dominance Incomplete Dominance –Blending of alleles to form intermediate trait Codominance –Both alleles are expressed simultaneously

Variations of Mendel’s Idea Multiple Alleles –ABO Blood Types –I A and I B dominant to i Pleiotropy –Genes affect more than one phenotype Polygenic Inheritance –Multiple genes affect a single phenotype –Creates a bell curve

Epistasis Gene at one locus alters the expression of a gene at another locus B = black b = brown C = color c = colorless

Nature vs. Nurture Genotypes create a norm of reaction Environment affects where the phenotype falls in that norm. Multifactorial: both genetic and environmental factors affect phenotype

Pedigree Analysis Pedigree: Genetic Family Tree Square = Male Circle = Female Filled = Expressed trait

Recessively Inherited Disorders Allele causes lack of protein production Heterozygous can still produce enough –Carriers Homozygous recessive often lethal

Types of Recessively Inherited Disorders Cystic Fibrosis –1/2500 whites from European ancestry –Generally dead before 5 years –Cl ion transport –Leads to mucus buildup causing infections Tay – Sachs Disease –Dysfunctional enzyme fails to break up brain lipid –Seizures, Blindness, degenerative motor and mental functions –1/3600 Jews of Central European ancestry –Dead around a few months

Recessively Inherited Disease (cont.) Sickle – cell Disease –1/400 African Americans –In low [O] concentration RBC become sickle shaped –Codominant allele –1/10 African Americans have sickle – cell trait –Trait remains due to resistance to malaria Inbreeding: Consanguineous mating (“same blood”) –Increases recessive traits –Shown as double lines on Pedigree

Dominantly Inherited Disorders Achondroplasia (form of Dwarfism) –1/10,000 –Dominant allele exists in.01% of population Huntington’s Disease –Lethal Neurodegenerative disease –Onset usually occurs around years –Located at tip of Chromosome 4 –GAC repeats, more repeats = earlier onset

Multifactorial Disorders Heart Disease DiabetesCancerAlcoholismSchizophrenia Manic - depressant

Technology and Genetic Screening Carrier Recognition: Remember GATTACA Fetal Testing –Amniocentesis: 10 mL of amniotic fluid –Chorionic Villus Sampling (CVS): suck out placental cells Cells undergoing Mitosis allow for 24 hour results –Ultrasound –Fetoscopy

Fetal Testing