Key Terms: 09_Genotype to Phenotype

Alleles (Coding vs. Regulatory)

Alleles can imply differences in coding regions or regulatory regions.

Gene

A section (locus) of DNA that encodes information. Typically refers to protein-coding DNA sequences plus regulatory DNA sequences.

Locus

The location of a gene on a chromosome.

Allele

Sequence variant of a gene. Different alleles code for different information.

Genotype

The genetic (allelic) composition of an individual.

Phenotype

A specific manifestation of a trait.

Trait

A heritable characteristic.

Lactose Intolerance / Tolerance (Primary)

In most mammals, lactase production stops after weaning because transcription of the lactase gene is turned down/off. Results in lactose intolerance.

Lactose Tolerance (Secondary)

In some humans, a mutation (SNP) in the promoter region of the lactase gene allows different transcription factors to bind, causing anomalously high transcription in adults. Results in lactose tolerance.

Lactase Gene Structure

Exons and introns plus a promoter and enhancer. The regulatory region is located in an adjacent gene.

Heterozygous

Two different alleles for one gene.

Homozygous

Two copies of the same allele for one gene.

Dominant Allele

Determines the phenotype even if only one copy is present.

Recessive Allele

Determines the phenotype only when two copies are present.

Starch Branching Enzyme (SBEI)

Enzyme that converts amylose to amylopectin (branched starch). Gene involved in pea texture. Slide connects enzymes, transposons, indels, genotype, and phenotype.

Environmental Influence on Phenotype (Complication 1)

Phenotype can be influenced by the environment.

Environmental Influences and Epigenetics

Environment can alter epigenetic marks (chromatin/DNA modifications) that change gene expression.

Non-Simple Dominance (Complication 2)

Alleles that are not simply dominant/recessive

Codominance / Incomplete Dominance

The information from both alleles is used in creating the phenotype (heterozygote RW shows a combined or intermediate phenotype).

Polymorphism (Complication 3)

Many alleles for a gene exist in a population. An individual still has just 2 alleles.

ABO Blood Groups (Primary)

Alleles I^A, I^B, and i. Products are glycoproteins in the red blood cell plasma membrane. Genotype → blood type - I^A I^A or I^A i = type A. I^B I^B or I^B i = type B. I^A I^B = type AB. ii = type O.

ABO Blood Groups (Secondary)

I^A and I^B are each dominant to i. Only ii gives type O. I^A and I^B are codominant, so I^A I^B gives type AB.

Multigenic (Polygenic) Traits (Complication 4)

Phenotypes controlled by more than one gene.

Quantitative Traits

Many genes produce a spectrum of phenotypes (examples

Epistasis (Complication 5)

One gene controls (overrides) other genes.