# does incest necessarily lead to birth defects?

## Recommended Posts

i'm talking about incest between close relatives, eg, father/daughter, mother/son, brother/sister

if it doesn't necessarily lead to birth defects, then what is the probability of it leading to defects?

i don't have a degree or any other qualification in biology so if you can answer this can you put it in simple language please. thanks

##### Share on other sites

In short, yes. Not only higher rates in birth defects but also infant mortality.

This article on (gasp) Wikipedia, gives some direct percentages on the chances for two alleles to be identical by descent (which is the problematic bit) > http://en.wikipedia....wiki/Inbreeding.

Edited by Microscope.com

##### Share on other sites

i'm talking about incest between close relatives, eg, father/daughter, mother/son, brother/sister

if it doesn't necessarily lead to birth defects, then what is the probability of it leading to defects?

i don't have a degree or any other qualification in biology so if you can answer this can you put it in simple language please. thanks

No, inbreeding does not necessarily lead to defects. Here is a chart from Wikipedia of some probabilities.

The inbreeding is computed as a percentage of chances for two alleles to be identical by descent. This percentage is called "inbreeding coefficient". There are several methods to compute this percentage, the two main ways are the path method[10] and the tabular method.[11][unreliable source?]

Typical inbreeding coefficient percentages are as follows, assuming no previous inbreeding between any parents:

• Father/daughter, mother/son or brother/sister → 25%
• Grandfather/granddaughter or grandmother/grandson → 12.5%
• Half-brother/half-sister → 12.5%
• Uncle/niece or aunt/nephew → 12.5%
• Great-grandfather/great-granddaughter or great-grandmother/great-grandson → 6.25%
• Half-uncle/niece or half-aunt/nephew → 6.25%
• First cousins → 6.25%
• First cousins once removed or half-first cousins → 3.125%
• Second cousins or first cousins twice removed → 1.5625%
• Second cousins once removed or half-second cousins → 0.78125%
• Third cousins or second cousins twice removed → 0.390625 %
• Third cousins once removed or half-third cousins → 0.195 %

Inbreeding

##### Share on other sites

^ what he said, in short

No not necessarily, but u increase the odds of displaying a recessive phenotype(form) the closer the relative u interbred with is. Also recessive phenotypes are not necessarily deleterious (harmful), although more than often they are.

An example of a neutral (non-harmful) recessive phenotype is white skin colour. (I could actually agrue positive for certain environments (cultures too but let's not ))

An example of a deleterious recessive phenotype is haemophilia.

Unfortunately not all genetics is that simple. Also for an idea of what close interbreeding produces, look at the genetics and evolutionary history of Cheetahs.

Edit: see also Sickle cell anemia, and interesting case where the hetrogenous type was favoured, while the homogenous type is fatal.

Edited by Sorcerer