“Traits & Genes ”

6.4 Traits, Genes, and Alleles KEY CONCEPT Genes encode proteins that produce a diverse range of traits

6.4 Traits, Genes, and Alleles A gene is a piece of DNA that tells a cell to make a certain protein. Each gene has a locus,Each gene has a locus, a specific position on a pair of homologous chromosomes

6.4 Traits, Genes, and Alleles For shape, there is a wrinkled allele and a round allele. They receive one allele from each parent.For shape, there is a wrinkled allele and a round allele. They receive one allele from each parent. An allele is an alternative form of a gene -Each parent donates one allele for every gene

6.4 Traits, Genes, and Alleles Genotype Homozygous (pure)Homozygous (pure) when both letters are the same when both letters are the same ex: TT, tt ex: TT, tt Heterozygous (hybrid)Heterozygous (hybrid) when letters are different when letters are different always write the big letter first always write the big letter first ex: Tt, Xx, Bb ex: Tt, Xx, Bb Dominant Alleles are always upper case and recessive alleles are always lower case.Dominant Alleles are always upper case and recessive alleles are always lower case.

6.4 Traits, Genes, and Alleles E. Mendel’s observed traits 1.Rule of Dominance: When a dominant trait is present the recessive trait is hidden

6.4 Traits, Genes, and Alleles Genes influence the development of traits. All of an organism’s genetic material is called the genome.All of an organism’s genetic material is called the genome. A genotype refers to the actual genes.A genotype refers to the actual genes. A phenotype is the physical expression of a trait.A phenotype is the physical expression of a trait.

6.4 Traits, Genes, and Alleles C. Genotype: 1. The gene combination of an organism It consists of 2 allelesIt consists of 2 alleles For example:For example: –PP –Pp –pp

6.4 Traits, Genes, and Alleles Phenotype :The appearance. The genotype determines the phenotype.The genotype determines the phenotype.

6.4 Traits, Genes, and Alleles Probability: The likelihood of an event. A probability is expressed as a percentage or a fraction.A probability is expressed as a percentage or a fraction. Genotypic Ratio: The ratio of genotypes that will appear.Genotypic Ratio: The ratio of genotypes that will appear. Phenotypic Ratio: The ratio of phenotypes that will appear.Phenotypic Ratio: The ratio of phenotypes that will appear. We can find the probability of a certain genotype or phenotype by constructing a Punnett Square.We can find the probability of a certain genotype or phenotype by constructing a Punnett Square.

6.4 Traits, Genes, and Alleles When a dominant allele always gets its way (the dominant phenotype is present no matter its partner) it is called COMPLETE DOMINANCE.When a dominant allele always gets its way (the dominant phenotype is present no matter its partner) it is called COMPLETE DOMINANCE. –Example: Pp = Purple Flower PP = Purple Flower Some times dominant traits don’t completely get their way……the alleles compromise. This results in a phenotype that is a mix of both parents. This is called INCOMPLETE DOMINANCE.Some times dominant traits don’t completely get their way……the alleles compromise. This results in a phenotype that is a mix of both parents. This is called INCOMPLETE DOMINANCE. –Example Pp = light purple flower

6.4 Traits, Genes, and Alleles In a few instances both alleles need to be expressed. This is called Codominance.In a few instances both alleles need to be expressed. This is called Codominance. –Example A mom chicken is black and dad chicken is white, but the baby chick comes out black and white.

6.4 Traits, Genes, and Alleles Most traits occur in a range and do not follow simple dominant- recessive patternsMost traits occur in a range and do not follow simple dominant- recessive patterns