Question

You are studying a pair of genes (A and B) that either gene alone can cause deafness. Deafness from Gene A is dominant. Deafness from Gene B is recessive. If both genes cause deafness, then you are deaf. You conduct the following cross: AaBb x AaBb What is the likelihood of an offspring with normal hearing

Answer 1

Answer:

3 individuals out of 16 are likely to have normal hearing

Explanation:

Available data:

• Two diallelic genes cause deafness, A and B
• Dominant allele A causes deafness (AA + Aa)
• Recessive allele a does not provoke deafness (aa)
• Dominant allele B does not provoke deafness (BB + Bb)
• Recessive allele b causes deafness (bb)

Cross:

Parentals)   AaBb    x     AaBb

Gametes) AB, Ab, aB, ab

                AB, Ab, aB, ab

Punnett square)    AB            Ab            aB            ab

                 AB       AABB     AABb      AaBB       AaBb

                 Ab       AABb     AAbb       AaBb       Aabb

                 aB       AaBB      AaBb       aaBB       aaBb

                 ab       AaBb      Aabb       aaBb       aabb

F1) Genotypes:

•     1/16 AABB (AA genotype causes deafness)
•     2/16 AABb (AA genotype causes deafness)

•     1/16 AAbb (AA and bb genotypes cause deafness)
•     2/16 AaBB (Aa genotype causes deafness)
•     4/16 AaBb (Aa gentoype causes deafness)
•     2/16 Aabb (Aa and bb genotypes cause deafness)
•     1/16 aaBB (neither genotypes cause deafness)
•     2/16 aaBb (Neigther genotypes cause deafness)
•     1/16  aabb (bb genotype causes deafness)

     Phenotypes:  

•     13/16 Deaf individuals, A-B- + A-bb, + aabb
•      3/16 not Deaf individuals, aaB-        

Answer 2

Answer:

BbxBb.

Explanation:

If Bb gene is crossed with Bb, the offspring is produced with normal hearing because both the genes are recessive in which the deafness gene hide and the hearing gene is dominant so the offspring can hear sounds clearly. The dominant A gene is responsible for deafness and we can see the offspring BbxBb in which no dominant gene is present. The other three offspring are deaf because of the presence of dominant A gene in their genetic makeup.