Classical and Modern Genetics

Overview An organism is diploid if it inherits two variants, or alleles, of each gene, one from each parent. These two alleles constitute the genotype …

Overview A Punnett square displays the possible genotypes offspring can inherit from two parental genotypes. If a trait’s inheritance pattern …

Overview In the 1850s and 1860s, Gregor Mendel investigated inheritance by performing monohybrid crosses in pea plants. He crossed two plants that were …

Overview To determine whether traits are inherited together or separately, Gregor Mendel crossed pea plants that differed in two traits. These parental …

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 …

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 of …

The Concept of Multiple Allelism Multiple allelism describes genes that exist in three or more allelic forms. Although diploid organisms, like humans, …

When more than one gene is responsible for a given phenotype, the trait is considered polygenic. Human height is a polygenic trait. Studies have uncovered …

In addition to multiple alleles at the same locus influencing traits, numerous genes or alleles at different locations may interact and influence …

Pleiotropy is the phenomenon in which a single gene impacts multiple, seemingly unrelated phenotypic traits. For example, defects in the SOX10 gene cause …

Many human characteristics, like height, are shaped by both nature—in other words, by our genes—and by nurture, or our environment. For …

When crossing pea plants, Mendel noticed that one of the parental traits would sometimes disappear in the first generation of offspring, called the F1 …

While Mendel’s Law of Segregation states that the two alleles for one gene are separated into different gametes, a different question of how …

In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be …

Like autosomes, sex chromosomes contain a variety of genes necessary for normal body function. When a mutation in one of these genes results in biological …

The human X chromosome contains over ten times the number of genes as in the Y chromosome. Since males have only one X chromosome, and females have two, …

Most DNA resides in the nucleus of a cell. However, some organelles in the cell cytoplasm⁠—such as chloroplasts and mitochondria⁠—also …

In 1866, Gregor Mendel published the results of his pea plant breeding experiments, providing evidence for predictable patterns in the inheritance of …

Alleles are different forms of the same gene. Humans and other diploid organisms inherit two alleles of every gene, one from each parent. An allele is …