i don’t understand . i thought there is no way to determine which is more common
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Dominant is *usually* more common, but not necessarily.
Brown eyes are a dominant allele, and indeed most humans on Earth have brown eyes, but in some northern European populations, blue eyes are the majority.
A dominant allele is especially likely to be rare if it causes health problems (or death). Achondroplasic dwarfism is caused by a dominant allele on a single gene. One copy causes the condition to be expressed, but two copies is almost always fatal.
Dominant and recessive have nothing to do with how common an allele is. What they mean is that if you get a dominant allele from one parent and a recessive allele from the other, then you will show the dominant trait. But it’s possible that only 1 in a million alleles are dominant, so the trait will be rare.
You can use statistics to estimate how common an allele is in a population. Let’s say that for some trait, the recessive allele is 60% and the dominant trait is 40%. For a person to show the recessive trait, they need two recessive alleles. Since the recessive allele is 60%, you would expect that the trait will show up in 36% of people(60% * 60%). If you know how common a trait is in a population and you know whether it’s recessive or dominant, you can work backwards and figure out how common the allele is.
Dominant and recessive have nothing to do with how common an allele is. What they mean is that if you get a dominant allele from one parent and a recessive allele from the other, then you will show the dominant trait. But it’s possible that only 1 in a million alleles are dominant, so the trait will be rare.
You can use statistics to estimate how common an allele is in a population. Let’s say that for some trait, the recessive allele is 60% and the dominant trait is 40%. For a person to show the recessive trait, they need two recessive alleles. Since the recessive allele is 60%, you would expect that the trait will show up in 36% of people(60% * 60%). If you know how common a trait is in a population and you know whether it’s recessive or dominant, you can work backwards and figure out how common the allele is.
Dominant is *usually* more common, but not necessarily.
Brown eyes are a dominant allele, and indeed most humans on Earth have brown eyes, but in some northern European populations, blue eyes are the majority.
A dominant allele is especially likely to be rare if it causes health problems (or death). Achondroplasic dwarfism is caused by a dominant allele on a single gene. One copy causes the condition to be expressed, but two copies is almost always fatal.
Brown eyes being more common doesn’t mean the recessive alleles is less common. Brown eyes are the phenotype but the presence or absence of an allele is the genotype
Brown eyes being more common doesn’t mean the recessive alleles is less common. Brown eyes are the phenotype but the presence or absence of an allele is the genotype
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