Essential knowledge 3.C.1: Changes in genotype can result in changes in phenotype.

Essential knowledge 3.C.1: Changes in genotype can result in changes in phenotype.
a. Alterations in a DNA sequence can lead to changes in the type or amount of the protein produced and the consequent phenotype. [See also 3.A.1]
Evidence of student learning is a demonstrated understanding of the following:

1. 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.
   

b. 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.

Evidence of student learning is a demonstrated understanding of the following:

1. Whether or not a mutation is detrimental, beneficial or neutral depends on the environmental context. Mutations are the primary source of genetic variation.

c. Errors in mitosis or meiosis can result in changes in phenotype.
Evidence of student learning is a demonstrated understanding of each of the following:

1. Changes in chromosome number often result in new phenotypes, including sterility caused by triploidy and increased vigor of other polyploids. [See also 3.A.2]

2. Changes in chromosome number often result in human disorders with developmental limitations, including Trisomy 21 (Down syndrome) and XO (Turner syndrome). [See also 3.A.2, 3.A.3]

d. 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. [See also 1.A.2, 1.C.3]
To foster student understanding of this concept, instructors can choose an illustrative example such as:

• Antibiotic resistance mutations 
• Pesticide resistance mutations 
• Sickle cell disorder and heterozygote advantage
  

Evidence of student learning is a demonstrated understanding of the following:

1. Selection results in evolutionary change.
   

Essential knowledge 3.C.2: Biological systems have multiple processes that increase genetic variation.

a. The imperfect nature of DNA replication and repair increases variation.

b. The horizontal acquisitions of genetic information primarily in prokaryotes via transformation (uptake of naked DNA), transduction (viral transmission of genetic information), conjugation (cell-to-cell transfer) and transposition (movement of DNA segments within and between DNA molecules) increase variation. [See also 1.B.3]

✘✘ Details and specifics about the various processes are beyond the scope of the course and the AP Exam.

c. Sexual reproduction in eukaryotes involving gamete formation, including crossing-over during meiosis and the random assortment of chromosomes during meiosis, and fertilization serve to increase variation. Reproduction processes that increase genetic variation are evolutionarily conserved and are shared by various organisms. [See also 1.B.1, 3.A.2, 4.C.2, 4. C3]

✘✘ The details of sexual reproduction cycles in various plants and animals are beyond the scope of the course and the AP Exam. However, the similarities of the processes that provide for genetic variation are relevant and should be the focus of instruction.

Essential knowledge 3.C.3: Viral replication results in genetic variation, and viral infection can introduce genetic variation into the hosts.

Viral replication differs from other reproductive strategies and generates genetic variation via various mechanisms. [See also 1.B.3]

Evidence of student learning is a demonstrated understanding of each of the following:

1. Viruses have highly efficient replicative capabilities that allow for rapid evolution and acquisition of new phenotypes.
   
2. Viruses replicate via a component assembly model allowing one virus to produce many progeny simultaneously via the lytic cycle.
   
3. Virus replication allows for mutations to occur through usual host pathways.
   
4. RNA viruses lack replication error-checking mechanisms, and thus have higher rates of mutation.
   
5. Related viruses can combine/recombine information if they infect the same host cell.
   
6. HIV is a well-studied system where the rapid evolution of a virus within the host contributes to the pathogenicity of viral infection.
   

b. The reproductive cycles of viruses facilitate transfer of genetic information.
Evidence of student learning is a demonstrated understanding of each of the following:

1. Viruses transmit DNA or RNA when they infect a host cell. [See also 1.B.3]

To foster student understanding of this concept, instructors can choose an illustrative example such as:
• Transduction in bacteria 
• Transposons present in incoming DNA

Some viruses are able to integrate into the host DNA and establish a latent (lysogenic) infection. These latent viral genomes can result in new properties for the host such as increased pathogenicity in bacteria.