Lethal Genes: Definition, Meaning, Topics, examples

What Are Lethal Genes?

Lethal genes are genes that kill an organism when present in any genotype. They come in several forms and may have very serious effects on the progress of the development and survivability of the organism. These genes may be either dominant, recessive, or conditional and cause death at very different stages of an organism's life cycle: embryonic, post-natal, or adult stages.

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This Story also Contains

1. What Are Lethal Genes?
2. Types Of Lethal Genes
3. Mechanisms Of Lethal Gene Action
4. The Recommended Video On Lethal Genes:

The concept of lethal genes is nearly as old as genetics itself. Early geneticists had learned by the beginning of the 20th century that certain allele combinations could result in nonviable offspring. Some of this seminal work, done in the early 1900s by the most influential workers in the field, including Lucien Cuénot and William Bateson, outlined the basic principles of how particular mixtures of genes could have lethal characteristics. These early studies were usually performed on model organisms, such as mice and fruit flies, where lethal alleles were demonstrated to perturb normal development in such a manner that embryos or juveniles die before reproductive age.

There are several reasons for which the study of lethal genes is paramount. First, it provides insight into the basic principles of genetics and developmental biology. The study of lethal genes allows much to be learned regarding how such complex, life-or-death events are regulated from the time of conception through to adulthood. In humans and other organisms, lethal genes have a critical application in genetic counselling and also in genetic disease prevention. Knowing the lethal genes helps diagnose and understand the pattern of inheritance of a given genetic disorder, and thus in the formulation of management or prevention strategies. Last but not least, research into lethal genes in agriculture and conservation would be very important, for example, through an improved understanding of genetic diversity management and breeding programs.

Types Of Lethal Genes

Lethal genes are categorised as:

Recessive Lethal Genes

Recessive lethal genes are genes dealing with certain lethality only upon an organism's being homozygous for that allele—that is, having two copies of said lethal gene. These genes often sneak through the mask of heterozygous carriers having one normal allele and one lethal allele, as no deleterious effects occur on them. The classic case is cystic fibrosis in man; the person who has two duplicate copies of the gene suffers severally with symptoms normally causing early death when not properly attended to.

Dominant Lethal Genes

Genes that cause the death of the organism when a single copy of an allele is present. They are rather rare because they generally eliminate carriers from the population before they reproduce themselves. An example is that carriers of Huntington's disease who have one copy of such dominant lethal allele, develop a progressive neural degeneration, and their symptoms manifested usually in the mid-adulthood.

Conditional Lethal Genes

These are genes which can only bring about death in certain conditions of the environment. These include sensitivity to temperature or dietary requirements, among others. For instance, some bacteria may have a certain weakness which may convey lethal action at high temperatures but may allow survival at lower temperatures.

Balanced Lethal Genes

Balanced lethal systems refer to a pair of lethal genes that are maintained in the population due to the balance in lethal effects. All organisms having one lethal gene survive while those having both lethal genes die. Thus, genetic diversity may be maintained within a population; some genes, otherwise lethal, are preserved. The system of genetic lethal factors operating in the gametic stage is called the gametic lethal genes.

Gametic Lethal Genes

Gametic lethal genes are those genes that harm gamete viability (that is, sperm or egg cells). Therefore, fertilisation may not contain at all or the embryonic death rate becomes extremely high. Such genes are thus highly effective in breeding programs or conservation programs that require viable offspring.

Each Type—Examples

• Recessive Lethal Genes: cystic fibrosis, sickle cell anaemia in humans

• Dominant Lethal Genes: Huntington's disease, some kinds of dwarfism.

• Conditional Lethal Genes: Temperature-sensitive mutations in Drosophila.

• Balanced Lethal Genes: Lethal alleles in corn plants where particular combinations are not viable.

• Gametic Lethal Genes: Mutations for sterility in plants and animals concerning gamete formation.

Classification Of Genes Based On The Effect Of Survivability

Genes can also be classified based on their effect on the survivability of organisms.

1. Essential Genes: Necessary for survival; their mutations mostly lead to lethality.

2. Non-essential Genes: Not crucial for survival; an organism can survive without them although with lowered fitness.

3. Conditional Essential Genes: Needed for survival only under certain conditions.

Mechanisms Of Lethal Gene Action

The mechanism is described below:

Gene Mutations And Their Effects

Lethal genes most commonly arise from mutations that inactivate normal gene function. They include point mutations, deletions, insertions, and chromosomal abnormalities. Such changes lead to the impairment of vital cellular processes and generally result in developmental arrest or a failure of some essential physiological function.

Disruption Of Protein Function

Many lethal genes act through the production of defective proteins that cannot perform their desired functions. For example, a mutation in some genes for the enzymes of a metabolic pathway may produce non-functional enzymes that block certain metabolic steps, resulting in metabolic blocks and the accumulation of byproducts of metabolic intermediates, which eventually lead to cell death.

Interference With Metabolic Pathways

Lethal genes can also act on mechanisms involving interference with metabolic pathways requisite for survival. Deficiencies in enzymes, malfunctioning of receptors, and defective transporters can bring metabolic processes to a close and elicit critical system failures in the organism. For example, deficiencies in certain metabolic enzymes are capable of preventing energy production and causing cellular and organismal death.

Conclusion

Lethal genes are some of the very important genetic components that can easily end up causing an organism's death due to specific genotypic conditions. Their types—recessive, dominant, conditional, balanced, and gametic lethal genes—call for deeper assessment, together with how they are expressed, as quite fundamental in understanding most aspects of genetics and biology. Concern for lethal genes cuts across medical genetics to agriculture and generally into fields of study concerning conservation biology.

The Recommended Video On Lethal Genes: