Allele
One version of a gene. An organism has two alleles for each gene, one from each parent. A dominant allele shows its effect even with one copy. A recessive allele shows only with two copies.
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Analogy
Two settings on a dial, one from each parent.
Example
PP: purple (homozygous).Pp: purple (heterozygous).pp: white (homozygous).Three genotypes, two looks.
In practice
In pea plants, the allele for purple flowers (P) is dominant to the allele for white (p).
Practice
Flashcards
- What is the difference between genotype and phenotype?Genotype is the alleles an organism carries. Phenotype is the trait that shows.
- What is a heterozygote?An individual with two different alleles of a gene.
Interview questions
- Explain Mendel's law of segregation and use a cross between two heterozygotes to show the expected ratios.
- Alleles separate in gamete formation
- Each gamete has one allele
- Aa x Aa gives 1:2:1 genotype
- 3:1 phenotype ratio
Questions people ask
Does dominant mean most common?
No. Dominant describes how an allele behaves in a heterozygote, not how common it is in a population. Some dominant alleles are rare. Huntington's disease is caused by a dominant allele that few people carry, and many common traits, such as blood group O, are recessive.
What does homozygous and heterozygous mean?
Homozygous means the two alleles of a gene are the same, such as AA or aa. Heterozygous means they are different, such as Aa. A homozygous individual breeds true for that trait. A heterozygote carries a recessive allele hidden by the dominant one, and can pass it on.