Key Difference – Inbreeding vs Outbreeding
Breeding is a sexual reproductive method performed to produce offspring with desired or beneficial characteristics over generations. Desired individuals are selected and artificially crossed to make progenies. There are different types of breeding techniques. Inbreeding and outbreeding are two types. The key difference between inbreeding and outbreeding is that inbreeding is a process of mating or breeding genetically close relatives for 4 to 6 generations while outbreeding is a process of mating distantly related or unrelated individuals over 4 to 6 generations. Inbreeding reduces the genetic variation in progenies while outbreeding increases the genetic variation in progenies.
CONTENTS
1. Overview and Key Difference
2. What is Inbreeding
3. What is Outbreeding
4. Side by Side Comparison – Inbreeding vs Outbreeding
5. Summary
What is Inbreeding?
Inbreeding is a process of breeding or crossing genetically related parents over many generations. Closely related individuals such as siblings are selected for inbreeding. The progeny of inbreeding will show increased homozygosity. The main objective of inbreeding is to maintain desirable traits and eliminate undesirable traits from that population. However, inbreeding can result in a higher chance of expressing deleterious recessive mutations as shown in figure 01. Hence, there is a high probability in offspring of carrying deleterious recessive traits due to the increased homozygosity by inbreeding. This introduces the lower fitness levels in the progeny of inbreeding. This phenomenon is known as inbreeding depression. When inbreeding produces biologically offspring with lower fitness, they are unable to survive and reproduce. Hence the offspring with high homozygosity are easily prone to becoming extinct from the environment by natural selection; this is known as genetic purging.
Inbreeding is a breeding method used in selective breeding to develop a particular phenotypic trait in plants and animals by making pure lines.
Figure 01: Inbreeding of pony – An example of inbreeding depression
What is Outbreeding?
Outbreeding, also known as outcrossing, is a process of mating distantly related or unrelated two individuals. The selection of two individuals is made from two populations. The main objective of outbreeding is to produce offspring with superior characteristics or quality. These two individuals are phenotypically adapted to two different environments. Therefore the progeny of the outcross may not easily adapt to live in either environment because the outcross might produce the phenotype intermediate to the parents. It will not perfectly suit for the parental environments. Hence, outbreeding does not always produce increased fitness in offspring. Sometimes outbreeding can show lower fitness to withstand the parental environment. It is known as outbreeding depression. For example, an outcross between a large body-sized individual with a small body-sized individual may produce a medium sized offspring; the offspring may not be well adapted for parents’ environments.
In most occasions, outbreeding produces offspring with superior quality. The mixing of genomes of two different populations may result in offspring which is superior to either of its parents. This is known as outbreeding enhancement and increases the genetic variation of the new genome. This increased genetic variation becomes beneficial in order to protect from extinction due to various factors such as environmental stress. The mixing of genes between two unrelated individuals, also increases the masking effects of deleterious mutations occur by recessive alleles.
What is the difference between Inbreeding and Outbreeding?
Inbreeding vs Outbreeding |
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| Inbreeding is a technique of mating two genetically closely related parents over 4 to 6 generations. | Outbreeding is a breeding method done between distantly related or unrelated individuals selected from two populations. |
| Genetic Nature of Offsprings | |
| Offspring of inbreeding are more likely to be homozygous. | Outbreeding increases the heterosis or hybrid vigor in progenies. |
| Biological Fitness | |
| Inbreeding is more likely to produce biologically lower fitness progenies. | Outbreeding is more likely to produce offspring with biological fitness. |
| Genetic Variation of Genomes | |
| Inbreeding reduces the genetic variation of progeny genomes. | Outbreeding increases the genetic variation in progeny genomes. |
| Expression of Deleterious Recessive Mutations | |
| There is a high probability of continuing deleterious recessive mutation in inbreeding progenies. | Outbreeding reduces the chance of expression of deleterious recessive mutations in offsprings. |
| Adaptation to Environment | |
| Progeny has a low potential to adapt to changing environments. | Progeny shows higher potential to adapt to changing environments. |
| Main Objective | |
| The main objective of inbreeding maintaining beneficial traits and developing pure lines. | Outbreeding is done to produce offsprings with superior quality. |
Summary – Inbreeding vs Outbreeding
Inbreeding and outbreeding are two breeding techniques performed by plant and animal breeders. Inbreeding is done between close relatives to maintain beneficial traits over generations. Inbreeding increases the homozygosity in the offspring. It negatively affects the offspring by giving more chance to express deleterious recessive mutations. Outbreeding is performed between unrelated or distantly related individuals over several generations. Outbreeding produces genetically diverse offspring that have a higher potential of adapting to new environments. This is the difference between inbreeding and outbreeding.
Reference:
1. Monson, Christopher A., and Kirsten C. Sadler. “Inbreeding Depression and Outbreeding Depression Are Evident in Wild-Type Zebrafish Lines.” Zebrafish. Mary Ann Liebert, Inc., June 2010. Web. 29 May 2017
2. “Inbreeding.” Wikipedia. Wikimedia Foundation, 21 May 2017. Web. 29 May 2017. <https://en.wikipedia.org/wiki/Inbreeding>.
3. “Outbreeding depression.” Wikipedia. Wikimedia Foundation, 05 May 2017. Web. 29 May 2017. https://en.wikipedia.org/wiki/Outbreeding_depression
4. “Outbreeding Enhancement (Heterosis).” The Free Dictionary. Farlex, n.d. Web. 29 May 2017. <http://encyclopedia2.thefreedictionary.com/Outbreeding Enhancement (Heterosis)>.
Image Courtesy:
1. “Shetland pony inbred” By en: User: ImaginaryFriend – en:File: Shetland pony inbred.JPG (Public Domain) via Commons Wikimedia