Your high school crush is working with a breed of guinea pig in which the side o

Question

Your high school crush is working with a breed of guinea pig in which the side on which the hair parts down the back is inherited, and it can either be on the left or the right. Left-parting appears to dominant in this system S/hethey crosses true-breeding parents that are phenotypically left parters and gets a generation of right-parters. Inbreeding the F1 produces a generation that consists entirely of lehi marters £ How is this uait transmitted? g. What are the genotypes of the parents and the genotypic ratiI and the F2? h. What was the genotype of the mother of the original female parent? Amazingly for rodents, some of these guinea pigs have enlarged carine teeth or 'fangs.. and your former crush notes that more males have fangs than do females. S/he/they crosses true-breeding fanged males to true-breeding fanged females and produces a generation in which males have fangs but females to not. Inbreeding the F1 produces piggies that have the following ratios Males: 3 fanged: I fangless Females: 1 fanged: 3 fangless. i. Is this trait sex-linked or autosomal? j. If autosomal, how do you explain the fact that the phenotypic ratios differ by

Explanation / Answer

f. This trait is transmitted through autosomes.

--> In Y-linked, only males are affected and only one trait is expressed, which is not the case here given above. So, it is not Y-linked.

--> In X-linked, when the parents are phenotypically dominant (left parting) , F1 should always contain dominant (left parting) female individual and no recessive (right parting), due to inheritance of dominant allele from their male parent (which contains dominant allele on its only X-chromosome). But, here dominant individuals are absent in F1. So, it is not X-linked.

--> In autosomal, there is a chance of getting receive individuals, when both parents are heterogeneous dominant, due to combination of recessive alleles from both parents (receiving one from each parent). So, this could be autosomal inheritance.

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g. GENOTYPES OF THE PARENTS: As said above, both parents should be heterogeneous dominant. Therefore, the genotypes are : Ll

--> Dominant allele = L (left parting) (capital l)

--> Recessive allele = l (right parting) (small l)

  GENOTYPIC RATIOS:

--> Genotypic ratio of F1 is 1 : 2 : 1 ( LL : Ll : ll )

--> Genotypic ratio of F2 is

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h. The genotype of mother of original female parent was : LL or Ll or ll . Because this is autosomal & not X-linked.

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i. This is autosomal (sex-influenced). Dominant in males & recessive in females.

--> In sex linked (X) , when both parents are fanged, the female should be fanged because they receive the fanged allele from their male parent, which should be exexpressed. So, it is not sex linked.

--> In autosomal, it can be possible that female can be fangless. So, it is autosomal.

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j. Autosomal ; sex influenced : Even though it is autosomal , the phenotypic ratios are influenced by sex hormones which are particular to that sex (male or female). Hence , it is called sex influenced.

--> In this case, the trait is dominant in males and recessive in females. Reason may be due to suppression of traits by female hormones which are absent in males, therefore expressed more in males.

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