Genes Genes Observable traits are the result of
Genes • Genes • Observable traits are the result of genes. – Genes are found on the chromosomes in our cells – Each observable trait is determined by two genes, one gene coming from each parent – A potential gene that a parent can pass to their offspring is called an allele
• Alleles are expressed using letters – Capital letters represent a dominant allele – Lower case letters represent a recessive allele • Each trait that we see is represented by two alleles, one randomly coming from each parent • Example: we might write eye color as Bb
• Allele Rules • Dominant allele will always show over recessive allele, ex. BB, Bb, or b. B would show the dominant trait • Order does not matter • The only way to see a recessive trait is to have a pair of recessive alleles, ex. bb • Exact matching alleles are called homozygous or pure, ex. BB or bb • Different allele pairs are called heterozygous or hybrid, ex. Bb
• Genotype • Phenotype • The written form of an observable trait using letters, ex. BB, Bb, b. B, bb • The appearance of the offspring based on the allele pairs given to them by their parents, what we see, ex. Blue eyes
• Punnett Squares • A tool used to organize the different possible combinations of alleles parents can pass on to their offspring • Each square of the Punnett Square represents a 25% chance the offspring will get a given pair of alleles
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