1. Patterns and Processes
of Inheritance
Classical Genetics
Pedigree Analysis
Technology

2. Classical Genetics
Mendel’s Laws
Genetic Crosses
Modes of Inheritance

3. 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:
Law of Dominance: Every trait is coded for by a pair of factors (alleles) one of which masks the effect of the other

4. Mendel’s Laws
Law of Segregation: During the formation of gametes the alleles for a trait separate so that each gamete has one allele for each trait
Law of Independent Assortment: the allele possessed by a gamete for one trait has no influence on the allele for any other trait

5. 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

6. 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

7. Modes of Inheritance There are 6 common modes of inheritance
Autosomal Dominant
Autosomal Recessive
Incomplete Dominance
Codominace
Intermediate Inheritance
Multiple Alleles

8. Modes of Inheritance
X-Linked Dominant
X-Linked Recessive
Y-Linked

9. Pedigree Analysis
Symbols
Analysis

10. Symbols
A pedigree chart is a representation of related individuals from several generations
Standard pedigree chart symbols are used in Biology 30

11. Analysis
Certain modes of inheritance of some traits can be determined from a pedigree chart
Autosomal Dominant
Autosomal Recessive
X-linked Dominant
X-linked Recessive

12. Technology
Selective Breeding
Genetic Counseling
Gene Mapping

13. 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

14. 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

15. 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

16. 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

17. 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