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