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Sample Problems
Patterns and Processesof Inheritance
Classical GeneticsClassical Genetics
Pedigree AnalysisPedigree Analysis
TechnologyTechnology
Sample Problems
Classical Genetics
Mendel’s LawsMendel’s Laws
Genetic CrossesGenetic Crosses
Modes of InheritanceModes of Inheritance
Sample Problems
Mendel’s Laws
• Gregor Mendel experimented with garden peas in an attempt to explain the mechanism of inheritance of traits
• His data revealed the following rules of inheritance:
1. Law of Dominance: Every trait is coded for by a pair of factors (alleles) one of which masks the effect of the other
Sample Problems
Mendel’s Laws
2. Law of Segregation: During the formation of gametes the alleles for a trait separate so that each gamete has one allele for each trait
3. Law of Independent Assortment: the allele possessed by a gamete for one trait has no influence on the allele for any other trait
Sample Problems
Genetic Crosses
• The phenotype of an individual can be either heterozygous or homozygous for a particular trait
• Purebred individuals are homozygous for the trait
• Hybrid individuals are heterozygous for the trait (also called carriers)
• The mating of two individuals is called a cross
Sample Problems
Genetic Crosses• Monohybrid crosses involve two individuals
both heterozygous for the trait• Dihybrid crosses involve two individuals
both heterozygous for each of two traits• A punnet square is a useful way to
determine the genotypes and phenotypes from one and two trait crosses
• A test cross is a method for determining the genotype of an individual by crossing it with a homozygous recessive individual
Sample Problems
Modes of Inheritance
• There are 6 common modes of inheritance
1. Autosomal Dominant
2. Autosomal Recessive
3. Incomplete Dominancei. Codominace
ii. Intermediate Inheritance
4. Multiple Alleles
Sample Problems
Modes of Inheritance
5. X-Linked Dominant
6. X-Linked Recessive
7. Y-Linked
Sample Problems
Pedigree Analysis
SymbolsSymbols
AnalysisAnalysis
Sample Problems
Symbols
• A pedigree chart is a representation of related individuals from several generations
• Standard pedigree chart symbols are used in Biology 30
Sample Problems
Analysis
• Certain modes of inheritance of some traits can be determined from a pedigree chart
1. Autosomal Dominant
2. Autosomal Recessive
3. X-linked Dominant
4. X-linked Recessive
Sample Problems
Technology
Selective BreedingSelective Breeding
Genetic CounselingGenetic Counseling
Gene MappingGene Mapping
Sample Problems
Selective Breeding
• Selective breeding is the purposeful mating of individuals with certain traits to alter the population
• Inbreeding increases the frequency of a trait in a population so that individuals become more alike (also called artificial selection)
• Outbreeding increases the variation within a population so individuals become less similar
Sample Problems
Genetic Counseling
• Genetic counseling provides information and support to families who have members with birth defects or genetic disorders and to families who may be at risk for a variety of inherited conditions
• Genetic counsellors would use pedigree charts and genetic testing to determine the probabilities of certain traits
Sample Problems
Gene Mapping
• Gene mapping is the determination of the location of genes on a chromosome
• To construct a gene map several linked traits must be identified
• Linked traits are traits that are due to genes on the same chromosome
Sample Problems
Gene Mapping
• Linked traits can be unlinked if crossing over occurs
• Crossing over results in unexpected phenotypes resulting from genetic crosses
• The frequency of crossing over is greater if linked genes are far apart on the same chromosome
Sample Problems
Gene Mapping
• By examining the offspring of genetic crosses it is possible to determine the frequencies of crossing over for several traits
• The crossover frequencies can be used to construct a gene map