Key Difference – Heterosis vs Inbreeding Depression
Breeding is a process which is used to create or produce offspring with desired phenotypes. Plant breeding is a common practice to develop new varieties and cultivar with beneficial characteristics. Inbreeding and outbreeding are two common breeding techniques employed by breeders. Inbreeding is the process of mating individuals which are genetically closely related. Inbreeding increases the homozygosity in progenies. Outbreeding is performed between two individuals who are unrelated or distantly related. Outbreeding facilitates the mixing of genes and increases the genetic variation in progenies. Inbreeding depression and heterosis are two terms related to inbreeding and outbreeding respectively. The key difference between heterosis and inbreeding depression is that heterosis is the enhancement of traits due to the mixing of genes from two different individuals during outbreeding while inbreeding depression is the reduced biological fitness of offspring due to the increased homozygosity as a result of inbreeding between closely related individuals.
CONTENTS
1. Overview and Key Difference
2. What is Heterosis
3. What is Inbreeding Depression
4. Side by Side Comparison – Heterosis vs Inbreeding Depression in Tabular Form
5. Summary
What is Heterosis?
Heterosis or hybrid vigor is the enhancement of the traits of the offspring over the traits of parents. This enhanced characteristics or superior nature is described as heterosis. This happens due to high genetic variation in the genomes of the offspring. Genetic variation increases when genetically different parents mate with each other. Heterosis is shown due to dominance or overdominance. The offspring are more adapted to the environments since they possess higher levels of fitness.
Breeding programs always attempt to develop offspring with desired characteristics or improved characteristics. Hence, breeders tend to perform crossbreeding or outbreeding than inbreeding. The main objective of crossbreeding is to achieve heterosis in offspring. Crossbreeding is more likely to produce offspring with superior characteristics than parent’s characteristics.
What is Inbreeding Depression?
Inbreeding is a mating process performed between genetically close individuals. In small populations, mating with relatives is common among animals. It increases the homozygosity in the successive generations and reduces their biological fitness. The reduced level of biological fitness in the offspring resulting from inbreeding is known as inbreeding depression. The progenies are unable to reproduce as well as survive in the changing environments. Increasing homozygosity causes reduction of genetic variation in the genomes of their offspring. Therefore, these individuals are less adapted to the environment. When the genetic variation in the genome is less, offspring are more likely to be subjected to inbreeding depression; when there is a high genetic variation in the genomes, they are less likely to be subjected into inbreeding depression. Inbreeding depression highly affects small populations restricted to small areas, but it does not affect a larger population spread in a bigger area.
Inbreeding increases the expression of deleterious recessive allele expression in offspring. When F1 population is transmitted with one deleterious recessive allele, inbreeding between F1 progeny produces the homozygous recessive allele in offspring. Hence, the deleterious recessive allele expression can be observed in the progeny as a result of inbreeding.
Figure 02: Inbreeding depression
What is the difference between Heterosis and Inbreeding Depression?
Heterosis vs Inbreeding Depression |
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| Heterosis is the phenomenon which enhances the traits in the hybrid offsprings than those of their parents due to genome mixing or outbreeding. | Inbreeding depression is a phenomenon which describes the reduced level of biological fitness in hybrid offsprings due to inbreeding. |
| Parental Genome | |
| Heterosis develops due to the mating of two different individuals which possess different genomes. | Inbreeding depression is caused due to mating between close relatives. |
| Genetic Variation of Genomes | |
| Heterosis is a result of high genetic variability between the genome of the parents. | Inbreeding depression is a result of low genetic variation. |
| Adaptation to Environment | |
| Offspring which show heterosis are well adapted to the environment. | Offspring are unable to adapt to the changing environment. |
| Characteristics | |
| Offspring show superior characteristics than their parents. | Offspring show inferior characteristics than their parents. |
Summary – Heterosis vs Inbreeding Depression
Inbreeding lowers offspring’s ability to survive and reproduce by reducing the biological fitness. This phenomenon is known as inbreeding depression. It is caused due to increased homozygosity in the genomes of the offspring. Outbreeding is performed between unrelated individuals and it enhances the gene mixing and genetic variation in the genomes of its offspring. Most of the traits are enhanced by the genome mixing between distantly related or unrelated individuals. This phenomenon is known as outbreeding enhancement or heterosis. Heterosis can be simply explained as hybrid offspring showing superior characteristics to those of their parents; inbreeding depression is the opposite of heterosis, where hybrids show inferior characteristics to those of their parents. This is the difference between heterosis and inbreeding depression.
References:
1.” Heterosis.” Wikipedia. Wikimedia Foundation, 22 May 2017. Web. Available here [Accessed 30 05 2017].
2.”What are the advantages and disadvantages of crossbreeding in dairy cattle?”Extension. N.p., n.d. Web. Availabe here [Accessed 30 May 2017].
3. Inbreeding and Inbreeding Depression. N.p., n.d. Web. Available here [Accessed 30 May 2017].