Mendel tracked heritable characters for three generations No Blending White determinant still there, just masked in F1
1. Discrete “genetic determinants” for each trait Alleles, alternative versions of a gene
Mendel’s law of segregation Phenotype 2. Determinants for trait separate into different gametes Genotype 3. Some determinants dominant over others (dominant and recessive traits) 4. Statistical occurrence of offspring supported random fusion of gametes predicted by laws of probability Punnett square
What experiment could you perform to determine the genotype for flower color of a pea plant with purple flowers?
What happens when you follow 2 traits? Do two traits assort together or independently? Dihybrid cross
What are Mendel’s 2 Law’s of Inheritance? Explain what each means as far as chromosomal alignment and movement in meiosis.
MENDEL’S LAWS OF INHERITANCE • Segregation of alleles • Independent assortment of different traits
How many unique gametes could be produced by independent assortment from an individual with the genotype AaBbCCDdEE ?
Solving Genetics Problems Consider the following cross: PpYyRr X Ppyyrr What is the probability of the phenotype Purple, Round, Yellow seed? What is the probability of the genotype PpYyRr?
What is the probability that each of the following pairs of parents will produce the indicated offspring? AABBCC x aabbcc AaBbCc AABbCc x AaBbCc AAbbCC
In sesame plants, one-pod(P) condition is dominant to 3-pod(p), and normal leaf (L) is dominant to wrinkled leaf (l). Pod type and leaf type are inherited independently. Determine possible genotypes of parents for all possible matings producing the following: 318 one-pod, normal leaf : 98 one-pod, wrinkled leaf 323 three-pod, normal leaf : 106 three-pod, wrinkled leaf
Mendel was not only smart, but extremely lucky. All his traits were dominant/recessive and on different chromosomes (or were far apart on a chromosome) Many inheritance patterns are more complex than simple dominant/recessive allele interactions.
Knowledge of the molecular basis of gene expression gives us a handle on understanding these different types of gene (allele) interaction and phenotypic expression. Genes code for proteins! Functional vs. nonfunctional enzymes, dosage affects, etc.
A and B are codominant, O is recessive to A and B Multiple alleles for the ABO blood groups
PLEIOTROPY One gene (or genotype) results in multiple phenotypes. Many different outward effects on the organism.
EPISTASIS -More than one gene involved. -A gene at one locus alters the phenotypic expression of a gene at a second locus.
POLYGENIC INHERITANCE -Multiple genes resulting in one phenotype. Ex. Skin color, eye color.
A simplified model for polygenic inheritance of skin color Environmental effects also affect the range of phenotype (multifactorial trait)
“Norm of reaction” for a genotype is the range of phenotype due to environmental influences. The effect of environment of phenotype Soil acidity effects the color of hydrangeas.
HUMAN GENETICS How do we study genetic traits in humans???
= male Pedigree analysis = female
HUMAN GENETIC DISORDERS WITH MENDELIAN INHERITANCE Recessive disorders: Heterozygous “carriers” are usually phenotypically normal. -Albinism -Cystic Fibrosis: most common lethal genetic disease in U.S. (1/2500 white population) -Tay Sachs: 1/3600 in Jewish population -Sickle Cell: 1/400 African Americans Example of “balanced polymorphism”
Dominantly inherited disorders: Dwarfism (Achondroplasia) 1/10,000 Dominant lethals rare (usually don’t survive to pass on gene) -Huntington’s Disease