A geneticist discovers an obese mouse in his laboratory colony. He breeds this obese mouse with a normal mouse. All the F1 mice from this cross are normal in size. When he interbreeds two F1 mice, eight of the F2 mice are normal in size and two are obese. The geneticist then intercrosses two of his obese mice, and he finds that all of the progeny from this cross are obese. These results lead the geneticist to conclude that obesity in mice results from a recessive allele. A second geneticist at a different university also discovers an obese mouse in her laboratory colony. She carries out the same crosses as the first geneticist and obtains the same results. She also concludes that obesity in mice results from a recessive allele. One day, the two geneticists meet at a genetics conference, learn of each other\'s experiments, and decide to exchange mice. They both find that, when they cross two obese mice from the different laboratories, all the offspring are normal. However, when they cross two obese mice from the same laboratory all the offspring are obese. Explain their results by drawing crossing diagrams and assigning genotypes and phenotypes to each parent and offspring. Solution The first scientist has detected an obese allele ---> recessive His identified alleles ---> o1 (recessive) & the normal allele ---> O1 The series crosses; the obese allele has produce recessive Cross-1: possible genotype Phenotypes Obese recessive (o1o1) × Normal (O1O1) --->All normal (O1o1) (F1-generation) Cross-2: possible genotypes: The following cross is between F1 offspring Normal (Oo1) × normal (O1o1) ---> total eight normal genotypes includes O1O1 and O1o1 & two obese with genotypes o1o1 Cross 3: genotypes: Homozygous recessive obese (o1o1) × Obese (o1o1) ---> all are obese with genotypes “o1o1” The second geneticist has depicted that the obese mouse in colony --> obese allele as o2 (recessive) and the normal allele as O2 (dominant). It has found that the cross between mice in different laboratories generated normal mice even though gene loci different alleles are both recessive therefore, it can be concluded that the obese mice of different laboratories associated with “obese genes” mainly independent of each other The prospective genotypes of the obese mice are: Parents crosses: phenotype Obese mouse -1 (o1o1O2O2) × phenotype Obese mouse 2 (O1O1o2o2) --> All are normal mice with genotypes O1o1O2o2 in F1 generation.

1. A geneticist discovers an obese mouse in his laboratory colony. He breeds this obese mouse
with a normal mouse. All the F1 mice from this cross are normal in size. When he interbreeds
two F1 mice, eight of the F2 mice are normal in size and two are obese. The geneticist then
intercrosses two of his obese mice, and he finds that all of the progeny from this cross are obese.
These results lead the geneticist to conclude that obesity in mice results from a recessive allele.
A second geneticist at a different university also discovers an obese mouse in her laboratory
colony. She carries out the same crosses as the first geneticist and obtains the same results. She
also concludes that obesity in mice results from a recessive allele. One day, the two geneticists
meet at a genetics conference, learn of each other's experiments, and decide to exchange mice.
They both find that, when they cross two obese mice from the different laboratories, all the
offspring are normal. However, when they cross two obese mice from the same laboratory all the
offspring are obese. Explain their results by drawing crossing diagrams and assigning genotypes
and phenotypes to each parent and offspring.
Solution
The first scientist has detected an obese allele ---> recessive
His identified alleles ---> o1 (recessive) & the normal allele ---> O1
The series crosses; the obese allele has produce recessive
Cross-1: possible genotype
Phenotypes
Obese recessive (o1o1) × Normal (O1O1) --->All normal (O1o1) (F1-generation)
Cross-2: possible genotypes: The following cross is between F1 offspring
Normal (Oo1) × normal (O1o1) ---> total eight normal genotypes includes O1O1 and O1o1 &
two obese with genotypes o1o1
Cross 3: genotypes:
Homozygous recessive obese (o1o1) × Obese (o1o1) ---> all are obese with genotypes “o1o1”
The second geneticist has depicted that the obese mouse in colony --> obese allele as o2
(recessive) and the normal allele as O2 (dominant).
It has found that the cross between mice in different laboratories generated normal mice even
though gene loci different alleles are both recessive therefore, it can be concluded that the obese
mice of different laboratories associated with “obese genes” mainly independent of each other
The prospective genotypes of the obese mice are:
Parents crosses: phenotype Obese mouse -1 (o1o1O2O2) × phenotype Obese mouse 2
(O1O1o2o2) --> All are normal mice with genotypes O1o1O2o2 in F1 generation