Lethal Gene and its Types

A gene that in some (such as homozygous) conditions may prevent development or cause the death of an organism or its germ cells — called also lethal factor, lethal mutant, lethal mutation.

Lethal Gene-

Types of Lethal Genes

There are different types of Lethal Genes

  1. Recessive lethal
  2. Dominant lethal
  3. Conditional lethal
  4. Balanced lethal
  5. Gametic lethal

1. Recessive lethal:

These are commonly found as most lethal are recessive. Their expression is in homozygous conditions only, hence survival of heterozygous ones is unaffected. They are a pair of identical alleles that ultimately result in the death of an entity.

2. Dominant lethal:

These are the alleles whose presence is required in one copy in an entity for them to turn fatal. These are not so frequently found as they cause the death of an entity before they are transmitted to their offspring.

3. Conditional lethal:

These alleles turn deadly only when there is an external environmental aspect involved.

4. Balanced lethal:

In a self permanent stock, the balancing effect between two different lethal is the balanced lethal system. The lethal genes that are associated in the repulsion stage of linkage are balanced lethal. They sustain themselves in the repulsion phase as a result of tight linkage. The recessive alleles in the repulsive stage of one gene and the dominant allele of the other gene are found to be present in the same chromosome. This lethal system sustains genes associated closely with the lethal genes in a permanent heterozygous state. Such lethal are observed in Drosophila, mice, etc.

5. Gametic lethal:

Gametic lethal are the ones that make the gametes incompetent to fertilize. Meiotic drive is often used to describe these types of lethal. This drive is a series of events which causes the production of unequal numbers by a heterozygote of functional gametes.

Several Genes Affecting the Same Character:

Character, in biology, any observable feature, or trait, of an organism, whether acquired or inherited. An acquired character is a response to the environment; an inherited character is produced by genes transmitted from parent to offspring (their expressions are often modified by environmental conditions).

One gene may affect many characters; one character may be controlled by many genes. A character controlled by only a few genes is known as an oligogenic or qualitative, character; oligogenic characters demonstrate discontinuous variation (in which traits are discrete; e.g., blood type is either AB, A, B, or O). A character controlled by many genes is known as polygenic, or quantitative; such characters demonstrate continuous variation (e.g., weight or height, each of which spans a range of values). A genetically controlled character may be described as dominant when its controlling genes are powerful enough to mask the effect of other genes (alleles) that control an alternative, or recessive, character.

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