Chapter 12

Classical and Modern Genetics

Genetic Lingo
Overview An organism is diploid if it inherits two variants, or alleles, of each gene, one from each parent. These two alleles constitute the…
Punnett Squares
12.2: Punnett Squares
Overview A Punnett square displays the possible genotypes offspring can inherit from two parental genotypes. If a trait’s inheritance pattern…
Monohybrid Crosses
12.3: Monohybrid Crosses
Overview In the 1850s and 1860s, Gregor Mendel investigated inheritance by performing monohybrid crosses in pea plants. He crossed two plants that…
Dihybrid Crosses
12.4: Dihybrid Crosses
Overview To determine whether traits are inherited together or separately, Gregor Mendel crossed pea plants that differed in two traits. These…
Pedigree Analysis
12.5: Pedigree Analysis
Overview A pedigree is a diagram displaying a family’s history of a trait. Analyzing pedigrees can reveal (1) whether a trait is dominant or…
Probability Laws
12.6: Probability Laws
Overview The probability of inheriting a trait can be calculated using the sum and product rules. The sum rule is used to calculate the probability…
Multiple Allele Traits
12.7: Multiple Allele Traits
The Concept of Multiple Allelism Multiple allelism describes genes that exist in three or more allelic forms. Although diploid organisms, like…
Polygenic Traits
12.8: Polygenic Traits
When more than one gene is responsible for a given phenotype, the trait is considered polygenic. Human height is a polygenic trait. Studies have…
Epistasis
12.9: Epistasis
In addition to multiple alleles at the same locus influencing traits, numerous genes or alleles at different locations may interact and influence…
Pleiotropy
12.10: Pleiotropy
Pleiotropy is the phenomenon in which a single gene impacts multiple, seemingly unrelated phenotypic traits. For example, defects in the SOX10 gene…
Nature and Nurture
12.11: Nature and Nurture
Many human characteristics, like height, are shaped by both nature—in other words, by our genes—and by nurture, or our environment. For…
Genetics: High-throughput Isolation of Temperature-sensitive Lethal Mutants
12.14: Genetics: 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…
Genetics: Optogenetic Random Mutagenesis
12.15: Genetics: Optogenetic Random Mutagenesis
Genetic screens uncover functionally important pathways in biological processes, although they often use toxic chemicals, carcinogens, or…
Developmental Biology: Mosaic Zebrafish Transgenesis
12.16: Developmental Biology: 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…