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Part 6.2: Inbreeding

Module 6: Evolutionary Mechanisms II - Mutation, Genetic Drift, Migration, and Non-Random Mating

What is inbreeding?

The mating of organisms or individuals that are closely related through common ancestry is inbreeding. Homozygosity is increased when inbreeding which means the frequency of AA will increase which will eventually become fixed for the A gene. The greater the degree of homozygosity the more uniform the offspring will be. [3] 

What are the benefits of inbreeding that may lead to the evolution of assortative mating?

Advantages of inbreeding include increased uniformity and prepotency (ability to pass on traits to offspring), and desired traits and breeding types can be fixed. Homozygosity is increased when inbreeding which means the frequency of AA will increase which will eventually become fixed for the A gene. The greater the degree of homozygosity the more uniform the offspring will be. [3] This may have lead to assortative mating in which pair bonds are formed on the basis of phenotypes when individuals organisms choose to mate those similar to themselves. [2]

What are some of the costs of inbreeding that may have prompted the evolution of inbreeding avoidance (disassortative mating)?

The disadvantages of inbreeding include lower fertility, lower "vigor", birth defects, smaller size, fewer offspring, slower growth, higher offspring, slower growth, higher offspring mortality, shorter lifespan, increase in genetic diseases,  and reduced "genetic potential" (ability to improve a trait). Inbreeding reduces fitness leading to inbreeding depression. The decrement in fitness is proportional to the degree of inbreeding. [3]


Figure 1: Cost of inbreeding [3]

The cost of inbreeding may have led to disassortative mating where opposites attract and individuals rather mate with individuals who are phenotypically different. 

Resources

[1] https://www.britannica.com/science/inbreeding

[2] https://www.britannica.com/science/assortative-mating 

[3] https://www.instituteofcaninebiology.org/blog/the-costs-and-benefits-of-inbreeding

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