Question

Coloration of stripes on snake skin is controlled by two genes. The dominant allele O for one gene leads to orange coloration. The corresponding recessive allele o does not give orange color. The dominant allele B for a separate gene leads to black coloration. The corresponding allele b does not give black color. When snakes that are homozygous for both the orange and black coloration genes are mated, what fraction of the offspring would be expected to have black coloration?

1) 1/2
2) 1/4
3) 3/4
4) 1/8

Answer 1

When homozygous snakes for orange (OO) and black (BB) coloration genes are mated, the offspring (OoBb) have a 1/4 chance of having black coloration due to the presence of at least one dominant allele for the black gene.Therefore the correct option is 2) 1/4.

Step-by-step explanation:

When snakes that are homozygous for both the orange (OO) and black (BB) coloration genes are mated, the offspring would inherit one allele from each parent. As both parents are homozygous dominant for both genes (OOBB x OOBB), all the offspring will receive one dominant allele for orange coloration (O) and one dominant allele for black coloration (B). The genotype of the offspring will be OoBb. The black coloration is determined by the presence of at least one dominant allele for the black gene. Therefore, 3 out of 4 possible combinations (OoBb, OOBb, OoBB) will result in black coloration. Hence, the fraction of the offspring with black coloration is 3/4.

In this genetic cross, the Punnett square can be used to visualize the possible genotypes of the offspring. The combinations OoBb, OOBb, OoBB represent individuals with black coloration, while the combination OoBB represents individuals with orange coloration. Since there are three favorable outcomes for black coloration out of four possible combinations, the fraction is 3/4.

In conclusion, the fraction of the offspring expected to have black coloration when snakes homozygous for both the orange and black coloration genes are mated is 1/4, as determined by the combination of alleles inherited from the homozygous parents.Therefore the correct option is 2) 1/4.