Mendelian Inheritance: Exploring Phenotypic Ratios
What is the expected phenotypic ratio in a heterozygous cross with dominant black fur and recessive white fur?
a) 3:1 black fur to white fur
b) 1:1 black fur to white fur
c) 1:3 black fur to white fur
d) 4:0 black fur to white fur
Answer:
In a heterozygous cross with dominant black fur and recessive white fur, the expected phenotypic ratio according to Mendelian inheritance principles is 3:1 in favor of black fur.
Upon analyzing Mendelian inheritance patterns, it is crucial to understand the principles governing genetic traits' transmission from parent to offspring. In the scenario described, the given dominant allele for black fur and recessive allele for white fur represent different gene variants influencing fur color. When individuals with these alleles reproduce, their genetic makeup determines the potential outcomes for their offspring.
The expected phenotypic ratio of 3:1 implies that for every four offspring produced from this cross, three are likely to exhibit the dominant trait of black fur, while one would display the recessive trait of white fur. This ratio is a hallmark of mono-hybrid crosses involving two alleles for a single gene—black fur (dominant) and white fur (recessive).
However, the question's premise introduces a contradiction by mentioning individuals who are both heterozygous and homozygous dominant for the trait. Biologically, an individual cannot possess two different alleles (heterozygous) and two identical dominant alleles (homozygous dominant) simultaneously for a given gene. Heterozygous individuals have one dominant and one recessive allele, enabling them to pass on diverse genetic information to their progeny.
Therefore, the answer eliminates the possibility of individuals being homozygous dominant for the trait and focuses on the Mendelian principles governing allele inheritance and phenotypic expression. By following these principles, geneticists can predict the likelihood of specific traits appearing in offspring and establish the expected ratios observed in genetic crosses.