Section 6.4 “Traits & Genes”

KEY CONCEPT Genes encode proteins that produce a diverse range of traits

What is a GENE? Basic unit of heredity. A section of DNA: from a few hundred DNA base pairs to more than 2 million base pairs It provides the instructions to make a particular protein.

Write one to two sentences that summarize the “What is a GENE?” Two minutes

A gene is the basic unit of heredity. A gene is a section of DNA. A gene provides the instructions to make a particular protein. A gene can vary in size from a few hundred DNA base pairs to more than 2 million base pairs.

A gene is the basic physical and functional unit of heredity A gene is the basic physical and functional unit of heredity. Genes, which are made up of DNA, act as instructions to make molecules called proteins. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases.

Most genes exist in many different forms. Different versions of the same gene are called Alleles. Each gene has a specific location on a chromosome. That location is called a Locus.

Example: Gene for flower color Each parent donates one version of that gene (allele)

Alleles can be Dominant or Recessive A dominant allele is expressed as a phenotype when at least one allele is present. A recessive allele is expressed as a phenotype only when two recessive alleles are present.

r R r r Dominant alleles are represented by uppercase letters Example: pea shape Dominant alleles are represented by uppercase letters Recessive alleles are represented by lowercase letters r R r r

If each parent donates the same version (allele), then they are called Homozygous Alleles. Example: wrinkled peas

If each parent donates a different version (allele), then they are called Heterozygous Alleles.

Think, write, pair share… Read your notes, think about the answer, write down your answer and then share your answer with your table partner. What is an allele?

Genes influence the development of traits Genome: All of an organism’s genetic material Includes genes and non-coding DNA

Genotype: two definitions 1. An organism’s complete set of genes ALSO… 2. Can refer to the combination of alleles that make up a specific gene or set of genes.

Genotype: the combination of alleles for a specific trait or set of traits.

Genotype The gene combination of trait It consists of 2 alleles For example: Pure dominant: BB = 2 dominant alleles “Homozygous” Pure recessive: bb = 2 recessive alleles “Homozygous Recessive” Hybrid: Bb = 1 dominant allele and 1 recessive allele “Heterozygous”

Let’s play – Guess the Genotype?

HOMOZYGOUS RECESSIVE: aa The rules are simple. A pair of alleles will pop up and YOU will have to guess whether the genotype is… HOMOZYGOUS: RR HOMOZYGOUS RECESSIVE: aa OR HETEROZYGOUS: Bb

T t M M E E B b f f D d a A g g e e Q q

Phenotype: the physical expression of a gene. The way an organism looks – the physical characteristics, or traits of an organism. Examples:

Let’s consider a gene for eye color Alleles: blue (recessive = b) Brown (dominant = B) Phenotype = Blue Eyes Phenotype = Brown Eyes Genotype = bb Genotype = Bb or BB

Mendel’s observed traits Dominant alleles: physical characteristics (traits) are observed if at least one dominant allele is present- covers up the other recessive traits. Recessive alleles: physical characteristics are observed ONLY if an organism receives BOTH recessive alleles (one from each parent). Rule of Dominance: When a dominant allele is present the recessive allele will be hidden, and the dominant trait will be expressed.

Mendel studied traits that follow simple dominant – recessive patterns of inheritance, and each trait was the result of a single gene. Most traits occur in a range and do not follow simple dominant-recessive patterns Many traits are determined by multiple genes Traits can also be influence by the environment