Genes to traits

Traits

Organisms, including people, have both inherited and acquired traits. Inherited and acquired traits are gained in different ways.

Inherited traits are passed down from biological parents to their offspring through genes. Genes are pieces of hereditary material that contain the instructions that affect inherited traits. Offspring receive their genes, and therefore gain their inherited traits, from their biological parents. Inherited traits do not need to be learned.

Acquired traits are gained during a person's life. Some acquired traits, such as riding a bicycle, are gained by learning. Other acquired traits, such as scars, are caused by the environment. Parents do not pass acquired traits down to their offspring.

Genes

Alleles, genotype, and phenotype

All organisms have pieces of hereditary material called genes, which are passed from parents to offspring. Genes contain instructions for building the parts of an organism. An organism's genes affect its observable traits, including its appearance, its behavior, and which diseases it may have. Genes may have different alleles, or forms, that can cause different versions of a trait.

For example, flower color is a trait in pea plants. The gene for this trait has two possible alleles. Each allele is represented by an uppercase or lowercase letter. The allele F is for purple flowers, and the allele f is for white flowers. Each pea plant has two alleles for the flower color gene—one allele inherited from each parent.

An organism's genotype for a gene is its combination of alleles for that gene. So, a pea plant may have a genotype of FF, Ff, or ff for the flower color gene.

An organism's phenotype for a trait is its observable version of that trait, which depends on the organism's combination of alleles. A pea plant may have a phenotype of purple flowers or white flowers for the flower color trait.

Homozygous and heterozygous

Some traits, like flower color in pea plants, are controlled by a single gene. Most plants and animals have a genotype made up of two alleles for these traits. These two alleles determine whether an organism is homozygous or heterozygous for the gene.

An organism with two identical alleles for a gene is homozygous for that gene. A pea plant with the genotype FF or ff is homozygous for the flower color gene.

An organism with two different alleles for a gene is heterozygous for that gene. A pea plant with the genotype Ff is heterozygous for the flower color gene.

Dominant and recessive

The types of alleles in an organism's genotype determine the organism's phenotype. Some alleles have types called dominant and recessive. These two types can cause different versions of a trait to appear as the organism's phenotype.

A dominant allele causes its version of the trait to appear even when the organism also has a recessive allele for the gene. In pea plants, the F allele, which causes purple flowers, is dominant over the f allele. A pea plant with at least one F allele will have the F allele's version of the flower color trait. So, a plant with the genotype FF or Ff will have purple flowers.

A recessive allele causes its version of the trait to appear only when the organism does not have any dominant alleles for the gene. In pea plants, the f allele, which causes white flowers, is recessive to the F allele. A pea plant with only f alleles will have the f allele's version of the flower color trait. So, a plant with the genotype ff will have white flowers.

Sexual Reproduction

Many organisms reproduce using a process called sexual reproduction. Sexual reproduction combines the genetic information of two individuals to produce new organisms. The two individuals are the parents. The new organisms are their offspring.

Mutation

An organism's genes contain information about its proteins. Each gene encodes, or contains the instructions for making, one protein or a group of proteins.

A permanent change in a gene is called a mutation.

Because a mutation changes a gene, the mutation may change the structure of the protein encoded by that gene.

The function of a protein depends on its structure. So, if a mutation in a gene changes a protein's structure, the mutation may also change the protein's function.

An organism's observable traits are affected by the functions of its proteins. So, a gene mutation that affects a protein's function may also affect an organism's observable traits.

Factors

Genetic factors have to do with an organism's genes. So, the set of genes a plant inherits from its parent is a genetic factor.

Environmental factors have to do with the conditions in an organism's surroundings. For plants, these conditions include the amount of light, water, and nutrients that are available to the plant. So, the number of hours of sunlight an orchid plant receives each day, the nutrients in the area where the orchid plant grows, and the amount of water the orchid plant gets are all environmental factors.