Sex Determination
Introduction: Sexual reproduction is the formation of offspring that are genetically distinct from their parents; most often, two parents contribute genes to their offspring. Among most eukaryotes, sexual reproduction consists of two processes that lead to an alternation of haploid and diploid cells: meiosis produces haploid gametes, and fertilization produces diploid zygotes. The term sex […]
Testcross
A useful tool for analyzing genetic crosses is the testcross, in which one individual of unknown genotype is crossed with another individual with a homozygous recessive genotype for the trait in question. A testcross tests, or reveals, the genotype of the first individual. “Cross fertilization of a phenotypically dominant individual with a homozygous recessive individual to […]
Monohybrid Crosses
Mendel started with 34 varieties of peas and spent 2 years selecting those varieties that he would use in his experiments. He verified that each variety was genetically pure (homozygous for each of the traits that he chose to study) by growing the plants for two generations and confirming that all offspring were the same […]
The Cell Cycle and Interphase
The cell cycle is the life story of a cell, the stages through which it passes from one division to the next. The cell cycle consists of interphase (a period of cell growth) and M phase (the period of nuclear and cell division). The cell cycle consists of two major phases. The first is interphase, the […]
Eukaryotic Cell Reproduction; chromosome structure
Like prokaryotic cell reproduction, eukaryotic cell reproduction requires the processes of DNA replication, copy separation, and division of the cytoplasm. However, the presence of multiple DNA molecules requires a more complex mechanism to ensure that one copy of each molecule ends up in each of the new cells. Eukaryotic chromosomes: are separated from the cytoplasm […]
Genetic Terminology
The term gene was a word that Mendel never knew. It was not coined until 1909, when the Danish geneticist Wilhelm Johannsen first used it. The definition of a gene varies with the context of its use, and so its definition will change as we explore different aspects of heredity. For our present use in […]
Mendel: The Father of Genetics
In 1902, the basic principles of genetics, which Archibald Garrod successfully applied to the inheritance of alkaptonuria, had just become widely known among biologists. Surprisingly, these principles had been discovered some 35 years earlier by Johann Gregor Mendel (1822 – 1884). Mendel was born in what is now part of the Czech Republic. Although his […]
A Brief History of Genetics
Although the science of genetics is young — almost entirely a product of the past 100 years — people have been using genetic principles for thousands of years. Prehistory: The first evidence that humans understood and applied the principles of heredity is found in the domestication of plants and animals, which began between approximately 10,000 […]
The Importance of Genetics
Although the science of genetics is relatively new, people have understood the hereditary nature of traits and have “practiced” genetics for thousands of years. The rise of agriculture began when humans started to apply genetic principles to the domestication of plants and animals. Today, the major crops and animals used in agriculture have undergone extensive […]
Royal Hemophilia and Romanov DNA
On August 12, 1904, Tsar Nicholas Romanov II of Russia wrote in his diary: “A great never-to-be forgotten day when the mercy of God has visited us so clearly.” That day Alexis, Nicholas’s first son and heir to the Russian throne, had been born. At birth, Alexis was a large and vigorous baby with yellow […]