Lake Tahoe Community College Bio 101
Intro to Cell and Molecular Biology Instructor: Sue Kloss
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Chapter 9 - Patterns of Inheritance
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I. Mendel’s principles
A. Experimental genetics began in an abbey garden
1. Gregor Mendel bred garden peas.
2. discrete heritable factors (today called genes)
3. Mendel could always be sure of parentage and offspring they produced
4. Mendel worked with plants until he had true breeding varieties in 7 characteristics
5. true breeding
6. hybrids
B. Mendel’s principle of segregation
1. of a single characteristic
2. F1, F2, P
3. Mendel developed 4 hypotheses
1. there are alternative forms of genes
2. organism has two genes, one from each parent
3. a sperm or egg carries only one allele for each inherited trait
4. dominant allele and recessive allele
4. how Mendel explained the results
a. Punnett square
5. Organisms appearance doesn’t always reveal genetic composition
a. genotype
b. phenotype
c. genotypic ratio
6. 6 inheritance patterns
7. Principle of Segregation
C. Homologous chromosomes
1. 2 sets of chromosomes - 1 moms, 1 dads
2. gene loci
3. Alleles (different forms of the same gene)
D. the Principle of Independent Assortment
1. crossing a parent homozygous dominant for both traits with a parent homozygous recessive for both traits
gave all heterozygotes in the F1
E. Geneticists use the testcross to determine unknown genotypes
F. Connections
1. genetic traits in humans can be tracked through family pedigree
2. many human inherited disorders are controlled by a single gene
3. fetal testing can spot many inherited disorders early in pregnancy
II. Variations on Mendel’s principles
A. The relationship of genotype to phenotype is rarely simple
1. genes are passed from generation to generation based on probability
B. Incomplete dominance results in intermediate phenotypes
C. Many genes have more than 2 alleles in the population
1. humans have 3 different alleles for blood type - A, B, and O.
2. Matching blood types is critical
3. People who have AB blood have antibodies for neither
7. Blood typing can be used in paternity suits
8. This gene exhibits codominance-
D. A single gene may affect many phenotype characteristics
1. pleiotropy
E. A single characteristic may be influenced by many genes
1. many characteristics are controlled by 2 or more genes.
Lesson Objectives – Homework Questions
1. Explain the distinction between each of the following pairs: gene and alleles, dominant and recessive, homozygous and heterozygous, phenotype and genotype, and monohybrid cross and dihybrid cross
2. Explain the experimental background of Mendel’s principle of segregation; define this principle, and explain its chromosomal basis.
3. Explain the experimental background of Mendel’s principle of independent assortment; define this principle and explain its chromosomal basis.
4. Review patterns of inheritance that do not follow Mendel’s principles, and give an example of each.
5. Describe the pattern of inheritance in sex linked characteristics.
6. Using Punnett squares, complete a monohybrid cross as well as a dihybrid cross.