Y-linked inheritance, a form of heredity wherein the pattern of inheritance is due to the acquired genes on the Y chromosome. © Biology Online. All rights reserved.
In biology, heredity refers to the passing of genetic factors from parents to offspring or from one generation to the next. The biological definition of heredity may also pertain to the genetic constitution of an individual organism. The term came from the Latin hērēditāt, which in English means “inheritance”. Thus, heredity is a synonym for biological inheritance. The term “hereditary” is a related word; it is used to describe or relate to “heredity”. Synonyms: (biological) inheritance.
Principles of heredity
Gregor Mendel, an Austrian monk, is considered as the father of genetics. (Ref.1) Genetics is the science that studies heredity and he laid the foundations to this field with his seminal works on garden pea plants. He formulated the laws of heredity, which is a set of generalizations from his empirical findings and statistical analysis. These generalizations attempt to explain heredity and inheritance pattern. They were based on Mendel’s conjecture that “unit factors” segregate and assort during gamete production. Then, these unit factors are passed on from parents to offspring. He further described the unit factors to exist in two sets, i.e. one from the mother and another from the father. Eventually, the unit factors were given the name “gene“. The genes inherited from the parents contain the information that determines the trait of the offspring. Other Mendel’s laws are Law of Dominance, Law of Segregation and Law of Independent Assortment. (Ref.2) The inheritance pattern that follows Mendel’s laws pertain to Mendelian inheritance. Conversely, an inheritance pattern that does not follow these laws is referred to as non-Mendelian.
Examples of heredity
Heredity is the means by which the offspring acquire characteristics from the parent. The passing of traits may be through sexual reproduction or by asexual reproduction. In sexual reproduction, male and female gametes are involved. The male gamete fertilizes the female gamete. Their union results in a single cell containing both chromosomal sets from the father and the mother. The new individual will, therefore, be genetically not identical to either of its parents. Conversely, in asexual reproduction, no gametes are involved. The offspring is genetically identical – “a clone” – of its parent. Biology Online Dictionary has further information to the different asexual means of reproducing, see asexual reproduction for more info. Below are examples of heredity in different organisms.
Heredity in bacteria and archaea
Both bacteria and archaea reproduce by binary fission. The process starts with the replication of genetic material, followed by chromosome segregation, and then cytokinesis. In essence, the bacterial or archaeal cell divides giving rise to two cells, each having the potential to grow to the size of the original cell. Since reproduction is by binary fission, the offspring is a clone of the parent. This means that both the parent and the offspring are genetically the same. However, both bacteria and archaea can exchange genetic material in a process called conjugation. The two cells, for instance, come together and join by a pilus, i.e. a short, filamentous projection that aids in bacterial cell adhesion. The two conjugating cells are temporarily joined via a pilus that also serves as a means to transfer genetic material in the form of a plasmid. Conjugation is crucial to many bacteria as it provides a way for acquiring genes, and thereby helps in expanding bacterial genome. The plasmid may contain genes that may be useful or not. A useful gene is one that carries a code for a protein with a desirable function, e.g. a protein that enables the recipient bacterial cell to persist in a condition that used to be lethal. Plasmid transfer, in fact, accounts for the emerging antibiotic resistance as plasmids from the antibiotic-resistant donor bacterial cell can transfer this feature to a recipient bacterial cell.
Heredity in sexually-reproducing organisms
Sexually-reproducing organisms include the eukaryotes. It should be noted, however, that not all eukaryotes reproduce either sexually or asexually. Some eukaryotes are capable of reproducing both by sexual and asexual means whereas others reproduce only sexually. Fungi, for example, are eukaryotic organisms wherein some of them reproduce through both ways whereas others reproduce by either means. (Ref.3) Those capable of reproducing asexually do so through fragmentation, budding, or spore production. Similar to bacteria and archaea and any other organism that reproduces asexually, the genome of the parent will pass on the same genome to the offspring.
In organisms that reproduce sexually, although the parent passes on its genes to its offspring, the offspring will be genetically distinct. Firstly, it is because only half of the genome will come from each parent. Secondly, during gametogenesis (the process of gamete formation), meiotic events, such as crossing over and independent assortment, occur and they promote genetic diversity among gametes. Thirdly, the genome of the offspring is comprised of the extranuclear genetic material from its mother. During fertilization, the union excludes the mitochondria from the sperm cell. Thus, the mitochondrial DNA will come from the mother. In humans, mitochondrial inheritance refers to an inheritance pattern resulting from the expression of the inherited mitochondrial DNA from the mother. Many of the known cases of mitochondrial diseases are attributed to the faulty mitochondrial DNA inherited from the mother although there are also few instances of mitochondrial diseases caused by the inadvertent entry of a faulty mitochondrial DNA from the father. Both of these do not conform to Mendelian inheritance.
- Mendelian inheritance
- Non-Mendelian inheritance
- Maternal inheritance
- Paternal inheritance
- Gregor Mendel | Biology Articles, Tutorials & Dictionary Online. (2020). Retrieved from Biology Articles, Tutorials & Dictionary Online website: https://www.biologyonline.com/dictionary/gregor-mendel/
- Mendels Law of Heredity | Biology Articles, Tutorials & Dictionary Online. (2020). Retrieved from Biology Articles, Tutorials & Dictionary Online website: https://www.biologyonline.com/dictionary/mendels-Law-of-Heredity/
- CK-12 Foundation. (2012, November 30). Fungi Reproduction. Retrieved from CK-12 Foundation website: https://www.ck12.org/biology/fungi-reproduction/lesson/Fungi-Reproduction-MS-LS/
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