Biology · MU Sofia

38. Effects of isolation: genetic drift, founder effect, inbreeding. Kinship and inbreeding coefficients.

Explains inbreeding as mating between relatives and how it reduces genetic variety and can bring rare harmful genes to light, including self-fertilisation as the extreme case and natural ways of avoiding it. Defines the inbreeding coefficient through identity by descent versus identity by state, and notes its link to parental relatedness and small isolated populations. Ends with a historical case study of the Spanish Habsburgs and their 'Habsburg jaw'.

Inside: 2 sections · 1 labelled picture · 3 min

Topic 38 of 64 in the MU Sofia syllabus for Biology (Dental Medicine, Year 1). The free AceMed note covers it in 2 sections, about 464 words (3 min of reading).

In this note

  1. Inbreeding
  2. The Spanish Habsburgs: A Study in Inbreeding

Inbreeding

  • What is Inbreeding?
  • Inbreeding happens when relatives mate. Unlike choosing a partner because of one similar trait, inbreeding affects many traits because related individuals share lots of genes.
  • Important Points:
  • Effects on Genes:
  • When relatives have children, the variety in their genes goes down. This is because they have many genes in common. For example, brothers and sisters share about half their genes.
  • Self-Fertilization:
  • The most extreme inbreeding is when an organism mates with itself, as some plants or hermaphrodites do. This makes their offspring very similar genetically, reducing gene variety a lot.
  • What Inbreeding Can Do:
  • Inbreeding can make rare genes show up more often, including ones that can cause health problems. This is why inbreeding can sometimes lead to weaker or sickly offspring.
  • Nature's Solutions:
  • Many plants and animals have ways to avoid inbreeding. Some plants can't fertilize themselves, and animals like lions kick young males out of the group to prevent them from mating with their relatives.
  • Summary:
  • Inbreeding is when relatives mate, leading to less variety in genes and sometimes causing health issues in offspring. Nature has ways to prevent it, ensuring healthier and more diverse populations.

Inbreeding Coefficient

  • What is the Inbreeding Coefficient?
  • It's a way to measure how inbred someone is. It tells us the chance that a person has the same gene versions from both parents because their parents are related.
  • Key Points:
  • Identical by Descent vs. Identical by State:
  • "Identical by descent" means the genes come from the same ancestor.
  • "Identical by state" means the genes look the same, but not necessarily from the same ancestor.
  • The inbreeding coefficient is about genes that are identical by descent.
  • How is it Measured?
  • The inbreeding coefficient (F) is half the relatedness of the parents unless they're also inbred, which makes F higher.
  • If the parents are not related, F is zero.
  • Inbreeding in Small Populations:
  • In small or isolated groups, eventually, everyone might be a bit inbred because there aren't many mating options.

Is Inbreeding Good?

  • While breeding for specific traits can make a purebred line with those traits, it can also bring out harmful genes.

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