ANY TIPS ON PEDIGREE ANALYSIS?

[Zebra]

Any tips? Everytime I see one, I freak out.
Is there a 'proper' way of doing this or is it simply trial and error?

and once I determine a particular allele is dominant/recessive + X-linked/Autosomal, how can reason for this?

plz help!

[malekv]

+1, please share your knowledge!

[nooshnoosh95]

what i do is

if its recessive i say two unaffected parents (eg. I-1 and I-2) produced affected offspring (II-1) therefore it must be recessive

and if its x-linked recessive id say the affected female (eg. I-2) produced all affected sons (II-2, II-3) but no affected daughters if her partner was unaffected

and if its autosomal id say there is an equal number of affected females and males
and if its dominant id say its present in every generation and two affected parents (I-1 and I-2) can produce unaffected offspring (II-4)

i think thats right

[Reckoner]

Pretty much what I do too. Also though, X-linked dominant traits: father with trait will pass it onto all of his daughters and none of his sons (if the mother doesn't have the trait).

[Zebra]

sometimes i will see a pedigree and kinda see what the answer is right?
BUT I can't explain it :S

[Ravit]

if you can get your hand on some TSFX notes they explain it really really well, would you like me to put up their summary for you?

[Reckoner]

What I tend to do then is to look at each different mating almost individually. I can then get an idea of the type of inheritance for that one mating. Once all different matings have been looked at, it will usually be clear which type of inheritance the trait is. Then to explain why it is, re look over each of the matings and think of the reasons that it is that form of inheritance in each of the mini-pedigrees. To write this down, use the specific individuals eg the affected mother II-2 passes the trait onto all of her sons (III-1, III-3) but none of her daughters (III-2, III-4), which indicates that the trait is x-linked recessive.

Hope you can understand what I'm trying to say. I think that's what I do, it's difficult to explain without an actual pedigree though.

[Ravit]

How to conquer a pedagree:D
 Step 1: if the condition appears in the pedigree from nowhere it must be recessive, eg if two uneffected parents have an affected child the child must be recessive

Step 2: If a trait is more common in a populaiton it does not necessarily mean that the trait is dominant.

Step 3: For X linked conditions, look for patterns of inheritance from fathers to sons and fathers to daughters, as fathers cannot pass an X Linked Trait to their sons. Also X dominant fathers, must pass the trait to all their daughters

Step 4: For X linked conditions look for patterns of traits from mothers to sons. X linked recessive mothers must pass that trait to all their sons

Step 5: Explaining the result of a pedigree:
Show a cross
Make a Statement, eg, the mode of inheritance of this is trait is blah blah

Step 6: successive births in a pedigree are independent events. Hence each offspring has the same probablity of inheriting the trait as its siblings

Posiible modes of inheritance

• Autosomal Recessive
  Autosomal Dominant
  Sex Linked Reccessive
  Sex Linked Dominant
  

 BIG TIP USE A PENCIL WHEN DOING THESE !

AutoSomal Dominant Conditions :
huntingtons, alzeimers
Both males and females are equallt effected
all individuals have at least one effected parent
transmission is from fathers to daughters and sons. OR from mothers to daughters and sons
Two affeced parents with the dominant trait can have uneffected recessive children

AutoSomal Recessive
both males and females are equally affected
Two unaffected heterozygous parents can have an affected offsring
Two recessive parents can onlt have recessive offspring

X-LinkeD Dominant
an affected male will pass the trait on to all his daughters
AN affected father cannot pass the trait to his sons
Sons who have the trait must have an affected mother
a female can pass the trait to all her daughters and sons
an affected person has at least one affected parent

X - Linked Recessive
all sons of an afffected mother show the trait
an affected mother must have an affected fatehr
an offspring from a mating between two individuals with the trait will exhibit the trait

[/list]

[zool3]

thanks ravit!

[Zebra]

WoW thanks man!!

actuary is the way to go

[Ravit]

no worries n-joy