Determining modes of inheritance

[Smiley_]

I having trouble doing these,
I have the atar notes book and even with reading the detailed solutions im still so confused

[swagsxcboi]

I having trouble doing these,
I have the atar notes book and even with reading the detailed solutions im still so confused

I'll be using R and r, R=dominant and r=recessive
it's either Autosomal Dominant, Autosomal Recessive, Sex-Linked Dominant, Sex-Linked Recessive
if it's autosomal dominant there is no way it can skip a generation, and any unaffected individual will be homozygous recessive. However, affected individuals can be either homozygous dominant or heterozygous. so you label every unaffected individual with rr. If their genotype is rr, then they must have inherited a 'r' allele from each parent. so you label each of the parents with '_ r '. If the parent is affected, their genotype is Rr, and if they are not affected, their genotype is rr. If this rule can work without any problems (and there is roughly an equal amount of females and males affected) then the mode of inheritance is autosomal dominant.
For autosomal recessive, any affected individual has the genotype rr. However, unaffected individuals can have either Rr or RR.
After labelling every affected individual with rr, you must realise that they have obtained a 'r' from each parent, so you label the parent as '_ r'. If the parent is not affected, the other allele must be R. If this can work throughout your entire pedigree, (and there is roughly an equal amount of females and males affected) then the mode of inheritance is autosomal recessive.
For sex-linked, you must understand that males=XY and females=XX
for sex-linked traits, the genes are located on the X chromosome only (males can not be carriers). Also, the father will always pass on his X chromosome to his daughter, so in sex-linked dominant, every affected father will have an affected daughter.
For sex-linked dominant, label every unaffected male as X^rY and every affected male as x^RY
Then you must trace back to their parents. The X chromosome of this individual came from mother and the Y chromosome came from the father. So you can label the mother as either X^rX^_ or X^RX^_
If you can do this without any problems, then the mode of inheritance is most likely sex linked dominant
For sex-linked recessive, label every unaffected male as X^RY and every affected male as X^rY
Again, you must trace back to the parents as label the mother as X^RX^_ or X^rX^_

I'm not the best teacher and I apologise if this wasn't useful

[the girl at the rock show]

I having trouble doing these,

Do you mean determining them from a pedigree chart or the results of a cross? (e.g. they give you a phenotypic ratio)

[Smiley_]

Do you mean determining them from a pedigree chart or the results of a cross? (e.g. they give you a phenotypic ratio)

both really arhh

[psyxwar]

Try watching this series of videos:

http://www.youtube.com/watch?v=HbIHjsn5cHo

[Smiley_]

Try watching this series of videos:

http://www.youtube.com/watch?v=HbIHjsn5cHo

thanks so much !!!!!!!!

[the girl at the rock show]

Here's a bit of advice on phenotypic ratios/crosses:

MONOHYBRID:
Aa x aa - phenotypic ratio is 1 dominant :1 recessive
Genotypic ratio: 1 Aa : 1 aa

Aa x aa - phenotypic ratio is 3 dominant: 1 recessive
3 (AA, Aa): 1 aa
Genotypic ratio: 1AA : 2 Aa : 1aa

Know about lethal alleles - for some genes, the homozygous dominant condition is lethal, so any zygote with AA will die during pregnancy (miscarriage). The results of the cross will be different to above.
For lethal alleles:
Aa x aa = 1Aa: 1aa (same as above since no offspring produced would be homozygous dominant)
BUT Aa x Aa = 2Aa : 1aa
I'm pretty sure it's also possible for lethal alleles to happen for the homozygous recessive condition for some genes.

DIHYBRID CROSS:

AaBb x AaBb - ratio is 9:3:3:1
9 dominant/dominant (AABB)
3 dominant/recessive (AAbb, Aabb)
3 recessive/dominant (aaBB, aaBb)
1 recessive/recessive (aabb)

Aabb x aabb - ratio is 1:1
1 dominant/recessive (Aabb)
1 recessive/recessive (aabb)

AaBb x aabb - ratio is 1:1:1:1
1 dominant/dominant (AaBb)
1 dominant/recessive (Aabb)
1 recessive/dominant (aaBb)
1 recessive/recessive (aabb)

If the genes are linked then the results will be different from above - 2 phenotypes will be more common.

Eventually, you should be pretty familiar with all the crosses above. My teacher says you shouldn't need a punnet square to work them out, especially the monohybrid crosses. And if you do a huge punnet square to work out the dihybrid phenotypes, you're just wasting time. So know them!

Hope I helped!

[sparked]

Autosomal Dominant: an affected child must have at least one affected parent.
Autosomal Recessive: can skip generations and appear random

X-linked recessive: Affected mothers have affected sons. Affected daughters have affected fathers.
X-linked dominant: affected sons have affected mothers. Affected daughters have at least one affected parent.

[ctoom14]

i found this recently, not to sure if it helps...