Question

1. A newly discovered species on the planet Neptune displays striped coloration controlled by a single gene. The first family sent as ambassadors to Earth has one parent with vertical stripes and one parent with horizontal stripes. Their child has a checkered pattern. What type of inheritance is being displayed? Predict the genotypes for all three individuals.

2. The ABO blood type locus has been mapped to chromosome 9. A father who has type AB blood and a mother who has type O blood have a child with trisomy 9 and type A blood. Using this information, can you tell in which parent the nondisjunction occurred?

Answer 1

Q1) As the Child has checkered pattern, it means that both the alleles (one for Vertical stripes and one for horizontal stripes) from two parents are expressed. This is not a case of Dominance-recessive relationship as the offsprings have both horizontal and vertical stripes which result if the checkered pattern. This is a case of co-dominance where both the alleles are equally dominant in the presence of other allele.

Consider the genotype of Parent with vertical Stripes as A1A1

and the genotype of parent with horizontal stripes as A2A2

Now cross the parents --------------->   A1A1    x A2A2

Gametes --------------------------------> A1 A2

Offspring genotype ----------------->    A1A2

(Here both Alleles A1 and A2 are expressed in the heterozygote as they are expressed in their homozygous condition, hence a case of co-dominance)

Q2) Blood group of father: AB

Genotype of father = IAIB

Blood Group of Mother = O

Genotype of Mother = IoIo

Consider the cross ----------------------> IoIo x IAIB

Consider if the Non-disjunction occurered in the male parent, Then male wil pass both the alleles to the gamete

Gametes --------------------------------> Io   IAIB

Offspring will be --------------------------->     IAIB Io (Trisomy)

(Blood group AB)

Consider the cross ----------------------> IoIo x IAIB

Consider if the Non-disjunction occurered in the female parent, Then female wil pass both the alleles to the gamete

Gametes --------------------------------> IoIo   IA   IB

Offspring will be --------------------------->     IoIo IA (Trisomy)    IoIo IB   (Trisomy)      

(Blood group A) (Blood group B)

Therefore Non-disjunction in the female parent leads to the offspring with blood group A

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