Section 6 4 Traits Genes and Alleles Biology

Section 6. 4: Traits, Genes, and Alleles Biology

Objectives v How does one gene have several versions of itself? v How do dominant and recessive alleles influence the development of traits? v How are alleles and phenotypes related

Genes v Mendel’s discrete unit of heredity v Gene: piece of DNA that provides a set of instruction that tell the cell to make a certain protein v Each gene has a locus, a specific position on a pair of homologous chromosomes v Genes exist in many forms

Forms Of Genes v Allele: an alternative form of a gene that exists at a specific locus v Cells have 2 alleles for each gene locus v One allele is found on each homologous chromosome v Each parent gave one allele

Alleles v Homozygous: Having two of the same allele at a specific locus v Heterozygous: Two different alleles at a specific locus

Genome v Genome: all of an organism’s genetic material v Each person has a unique genome, unless you have an identical twin v Some traits can be seen, while others cannot v Genotype: refers to the genetic makeup of a specific set of genes v Phenotype: Physical characteristics of an individual organism

Types Of Alleles v Dominant Allele: Allele that is expressed when two different alleles or two dominant alleles are present v Recessive: Allele that is only expressed when two copies are present v Dominant is NOT v stronger than a recessive allele v does not occur more often in the population

Representation Of Alleles v Alleles are represented by individual letters v Therefore, each organism’s genotype is expressed with two letters, one per allele v Dominant Allele: Use Uppercase letter v Recessive Allele: Use lowercase letter

Alleles & Phenotype v Two genotypes can produce the dominant phenotype v But, what make one allele dominant over another? v Based on the protein produced by that allele at that specific locus v Other factors affect phenotype: v Environment v Nutrition v Some traits are influenced by multiple genes v More on this later!