10 (c) Genotypes and Phenotypes p88
Phenotypes and Genotypes
Two useful terms that geneticists use are phenotype (fee noh typ) and genotype (jen uh typ). An organism’s phenotype is its physical appearance, or visible traits. An organism’s genotype is its genetic makeup, or allele combinations.
To understand the difference between phenotype and genotype, look at Figure 9. The allele for smooth pea pods (S) is dominant over the allele for pinched pea pods (s). All of the plants with at least one dominant allele have the same phenotype—they all produce smooth pods. However, the plants can have two different genotypes--SS or Ss. If you were to look at the plants with smooth pods, you would not be able to tell the difference between those with the SS genotype and those with the Ss genotype. The plants with pinched pods, on the other hand, would all have the same phenotype—pinched pods—as well as the same genotype--ss.
Geneticists use two additional terms to describe an organism’s genotype. An organism that has two identical alleles for a trait is said to be homozygous (hoh moh zy gus) for that trait. A smooth-pod plant that has the alleles SS and a pinched-pod plant with the alleles ss are both homozygous. An organism that has two different alleles for a trait is heterozygous (het ur oh zy gus) for that trait. A smooth-pod plant with the alleles Ss is heterozygous. Mendel used the term hybrid to describe heterozygous pea plants.
Two useful terms that geneticists use are phenotype (fee noh typ) and genotype (jen uh typ). An organism’s phenotype is its physical appearance, or visible traits. An organism’s genotype is its genetic makeup, or allele combinations.
To understand the difference between phenotype and genotype, look at Figure 9. The allele for smooth pea pods (S) is dominant over the allele for pinched pea pods (s). All of the plants with at least one dominant allele have the same phenotype—they all produce smooth pods. However, the plants can have two different genotypes--SS or Ss. If you were to look at the plants with smooth pods, you would not be able to tell the difference between those with the SS genotype and those with the Ss genotype. The plants with pinched pods, on the other hand, would all have the same phenotype—pinched pods—as well as the same genotype--ss.
Geneticists use two additional terms to describe an organism’s genotype. An organism that has two identical alleles for a trait is said to be homozygous (hoh moh zy gus) for that trait. A smooth-pod plant that has the alleles SS and a pinched-pod plant with the alleles ss are both homozygous. An organism that has two different alleles for a trait is heterozygous (het ur oh zy gus) for that trait. A smooth-pod plant with the alleles Ss is heterozygous. Mendel used the term hybrid to describe heterozygous pea plants.
