August 18, 2023

How to Determine If the Curl Allele is Dominant Or Ressive

Suppose you discovered a stray cat with unusually rounded, curled-back ears. Cat fanciers want to establish this cat as a new breed, and it’s important to determine whether the curl allele is dominant or recessive.

Scientists know that curly hair is caused by one dominant gene, and straight hair is caused by two recessive genes. In theory, if both parents have two genes for curly hair and one for straight hair, their kids will all have wavy or curly hair (the phenotype that results from the combination of your two alleles). However, in practice, this doesn’t always happen. One reason is that the dominant gene doesn’t completely suppress the appearance of the recessive gene. This is called incomplete dominance. It’s a little like having one brown-eyed parent and one green-eyed parent giving their kid hazel eyes.

The other reason is that many genes work together to control your phenotype, and not all of them are expressed at the same time. For example, the same genes that determine your hair type also influence your eye color. Gregor Mendel’s laws of inheritance tell us that each gene carries enough directions to control a specific trait, but most of the time genes interact with one another, and your phenotype is the result of how these genes combine with other factors, like your ethnicity.

To find out whether the curl allele is dominant or recessive, you can do a test cross. Matings of the original curl cat with a noncurl cat will produce both curled and noncurled F1F1 offspring, but only offspring with the curl allele if the allele is dominant.


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