Autosome or sex chromosome?

Question

How do you tell if a trait is carried on the autosome or sex chromosome?

I am supposed to determine whether the trait for 2 extra fingers is carried on the autosome or sex chromosome. They gave me the family history on the homework.

Answer 1

In below 2EF stands for 2 extra fingers phenotype.
Please look for the following patterns ONE BY ONE in the family history. You can start from the largest family, which has 2EF child(ren):
Patterns:
1) In any family, normal mother and normal father have 2EF daughter(s) -> autosome linked (stop here, definitive)
2) In the whole family history, only males are 2EF, no female is ever 2EF, and all of sons of a 2EF father are 2EF -> Y linked (stop here, definitive)
3) mother is 2EF, father is normal:
if no daughter is 2EF -> X linked recessive
around 50% of sons and 50% of daughters are 2EF -> X linked dominant
4) father is 2EF, mother is normal:
if all the daughters are 2EF -> X linked dominant
if all the daughter are NOT 2EF - X linked recessive
around 50% of sons and 50% of daughters are 2EF -> X linked recessive
5) both father and mother are 2EF:
if some of the sons are NOT 2EF -> X linked recessive

I hope you already get your answer by here. Please notice there are three assumptions in this genetic analysis:
a) 2EF is linked with single chromosome/loci/gene
b) the relationship in the family history is biological
c) X chromosome inactivation is not considered

Answer 2

Check the probabilities, as women have two X chromosomes and men have one. So, for a X linked recessive trait, such as color blindness men's chances of being homozygous for the trait are doubled. This will show in a family pedigree.

Answer 3

both contain genetic information. the sex chromosomes are the ones that determine if your a boy or a girl. two sex chromosomes X and Y. XX if your a girl and XY if your a boy. male determines gender as you can tell because females can only pass down an X. (during fertilization)

Answer 4

Is the trait dominant or recessive?
If it is recessive and the affected individuals are all or almost all males, then it's on the X-chromosome.

If it is recessive and both males and females are affected, then it's on an autosome.