Chapter 12

Classical and Modern Genetics

Genetic Lingo
Offspring receive one copy of each gene from each parent. Each copy represents an allele—different, but normal forms of the gene. Each pair of…
Punnett Squares
12.2: Punnett Squares
The Punnett Square—a simple diagram named after its inventor—is a graphical way to predict the likelihood that offspring may inherit a…
Monohybrid Crosses
12.3: Monohybrid Crosses
Before Gregor Mendel’s experiments, it was believed that the traits of offspring were a blended combination of their parents’ genes.…
Dihybrid Crosses
12.4: Dihybrid Crosses
In a genetic cross between diploid organisms, the offspring receive one copy of each gene from each parent. Each copy represents an…
Pedigree Analysis
12.5: Pedigree Analysis
Pedigree Analysis is a tool used to study the inheritance of traits. It is useful for visualizing the pattern of inheritance over several…
Probability Laws
12.6: Probability Laws
While the Punnett Square is a useful tool to visualize probability calculations for one or two genes, it can become cumbersome to use when the number…
Multiple Allele Traits
12.7: Multiple Allele Traits
Although many genes exhibit a dominant or recessive phenotype due to the expression of a single allele, in some genes, multiple alleles will interact…
Polygenic Traits
12.8: Polygenic Traits
When many genes are responsible for a given phenotype, the traits are considered polygenic. A good example is human height. Studies have uncovered…
Epistasis
12.9: Epistasis
In addition to multiple alleles, different genes—at different locations—may interact and influence phenotypes in a phenomenon called…
Pleiotropy
12.10: Pleiotropy
Pleiotropy is the phenomenon that results in a single gene impacting multiple seemingly unrelated phenotypic traits. For example, defects in the…
Nature and Nurture
12.11: Nature and Nurture
Many human characteristics, like height, are shaped by both nature—for example, by our genes—and by nurture, or our environment. Factors…
Genetic Screens
12.12: Genetic Screens
Genetic screens are critical tools for defining gene function and understanding gene interactions. Screens typically involve mutating genes and then…
SNP Genotyping
12.13: SNP Genotyping
Single nucleotide polymorphisms, or SNPs, are the most common form of genetic variation in humans. These differences at individual bases in the DNA…
High-throughput Isolation of Temperature-sensitive Lethal Mutants
12.14: High-throughput Isolation of Temperature-sensitive Lethal Mutants
Genetic knockouts are valuable for deciphering biological function. However, they can’t be generated for essential genes. This article…
Optogenetic Random Mutagenesis
12.15: Optogenetic Random Mutagenesis
Genetic screens uncover functionally important pathways in biological processes, although they often use toxic chemicals, carcinogens, or…
Mosaic Zebrafish Transgenesis
12.16: Mosaic Zebrafish Transgenesis
Cancers are marked by the accumulation of chromosome alterations that can affect multiple cell processes. In this study, transgenes are co-injected…