Essential Knowledge 3.C.1

Changes in genotype can result in changes in phenotype.

Alterations in a DNA sequence can lead to changes in the type or amount of the protein produced and the consequent phenotype. DNA mutations can be positive, negative or neutral based on the effect or the lack of effect they have on the resulting nucleic acid or protein and the

phenotypes that are conferred by the protein.

Errors in DNA replication or DNA repair mechanisms, and external factors, including radiation and reactive chemicals, can cause random changes, e.g., mutations in the DNA. Whether or not a mutation is detrimental, beneficial or neutral depends on the environmental context. Mutations are the primary source of genetic variation.

Errors in mitosis or meiosis can result in changes in phenotype. Changes in chromosome number often result in new phenotypes, including

sterility caused by triploidy and increased vigor of other polyploids. Changes in chromosome number often result in human disorders with

developmental limitations, including Trisomy 21 (Down syndrome) and XO (Turner syndrome).

Changes in genotype may affect phenotypes that are subject to natural selection. Genetic changes that enhance survival and reproduction can be selected by environmental conditions. Examples include antibiotic resistance mutations, pesticide resistance mutations, and sickle cell disorder and heterozygote advantage. Selection results in evolutionary change.

Students should be able to:

LO 3.24 Predict how a change in genotype, when expressed as a phenotype, provides a variation that can be subject to natural selection.

LO 3.25 Create a visual representation to illustrate how changes in a DNA nucleotide sequence can result in a change in the polypeptide produced.

LO 3.26 Explain the connection between genetic variations in organisms and phenotypic variations in populations.