TRAITS, GENES, AND ALLELES

Genes

KEY CONCEPT

Genes encode proteins that produce a diverse range of traits

by Mrs. Micich

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Main Ideas and Vocabulary

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Connect

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Genes have Variety

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Same or Different

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Genes Influence Traits

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Dominant and Recessive Alleles

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How to represent alleles

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Rap

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Sources

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MAIN IDEAS TO LOOK FOR

The same gene can have many versions
Genes influence the development of traits

VOCABULARY

Gene
Allele
Homozygous
Genome
Locus
Genotype
Phenotype
Dominant
Recessive

Take a minute to meet your guides below.

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various socks

CONNECT

Most things come in many forms. Ice cream can be vanilla, chocolate, or strawberry. Cars can be two-door, four-door, hatchback, or convertible. There are more varieties of apples than can be counted on two hands. Most genes have many forms, too.

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Portrait of Mendel

The same gene can have many versions.

Mendel, the father of genetics, studied units of inheritance called genes . You can think of a gene as a piece of DNA that stores instructions to make a certain protein. Each gene is located at a particular place on a chromosome called a locus .

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Mendel's peas

Now you know many things come in different forms. An allele is any of the different forms of a gene. Think of the peas Mendel studied, he noticed the gene for pea shape has two alleles - one for round peas and another for wrinkled peas.

Your cells, like the pea plant's cells, have two alleles for each gene - one each chromosome of a homologous pair.

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These alleles can br the same or they can be different.

Homozygous describes two of the same alleles at a specific locus or location. Both alleles could be the code for blues eyes.

Heterozygous describes two different alleles at a specific locus or location. One allele code for blue eyes and one allele code for brown eyes.

blue eye

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Genes influence the development of traits.

Have you heard of the Human Genome Project?

It's goal was to find out the sequence of the 3 billion nucleotide pairs that make up a human's genome .

This genome is an organism's genetic material. You have unique genome that determines all of your traits.

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Flower from a pea plant

Now you know a genome is all of an organisim's gene's.

But did you know a genotype is a specific set of genes and the phenotype is the physical characteristic of an individual organism.

Let's consider flowers, the genotype includes both of the genes that code for flower color. Even if one of those colors is hidden.

In contrast, if the flower is purple it has a phenotype for purple flowers. The plant might have hidden gene for white flowers, but that does not matter to its phenotype.

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Dominant and Recessive Alleles

If an organism is heterozygous for a trait, which allele will be expressed?

Let's go back to the example of flowers. If a plant has one allele for purple flowers and one allele for white flowers, what color will the flowers be?

A dominant allele is the allele that is expressed when two different alleles are present. A recessive allele is the allele that is only expressed when two copies are present.

In Mendel's experiments, the allele for purple flowers was dominant to the allele for white flowers. So all the plants were purple even though they had only one allele for purple flowers.

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How to represent alleles on paper.

Alleles are often represented with individual letters. An organism's genotype for a trait can be shown with two letters - one per allele.

UPPERCASE letters are used for dominant alleles, and lowercase letters are used for recessive alleles.