This pedigree shows the segregation of a rare disease in a...

'This pedigree shows the segregation of a rare disease in a family. What is the most likely mode of inheritance of this disease? (assume complete penetrance) autosomal recessive autosomal dominant X-linked recessive X-linked dominant maternal imprinting paternal imprinting'

Transcript

00:01 We are not told what the specific disease or trait is, but we are given this family pedigree and we're shown that there is some type of trait that's present in only a few family members across three different generations.

00:17 And we're asked about this family and what type of inheritance this trait has.

00:23 Okay, so i've listed all of the options for inheritance over to the right.

00:27 You can see that it could be y linked on the y chromosome, x linked on the x chromosome.

00:32 Autosomal dominant or autosomal recessive.

00:35 So just by looking at this picture, we can get a pretty good understanding of what mode of inheritance this will be.

00:45 So the easiest ones to look at are the sex -linked traits.

00:50 So starting with y -linked, it's the easiest.

00:53 If a trait is y -linked, it will only affect males because they are the only ones that have the y -chromosome.

00:59 We see that is not the case because there are two females that are positive for this trait, and so that one is not likely.

01:13 It could be x -linked, meaning it has to be on the x chromosome.

01:22 So it could be sort of dominant or recessive on the x chromosome.

01:31 However, if we look at just one family individually, we can tell that it is not going to be on an x chromosome.

01:37 We'll take this family, for instance.

01:43 We see that dad here does not have the trait...

Question

'This pedigree shows the segregation of a rare disease in a family. What is the most likely mode of inheritance of this disease? (assume complete penetrance) autosomal recessive autosomal dominant X-linked recessive X-linked dominant maternal imprinting paternal imprinting'

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