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

““Traits & Traits & GenesGenes””

6.4 Traits, Genes, and Alleles

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


A gene is a piece of DNA that A gene is a piece of DNA that tells a cell to make a certain tells a cell to make a certain protein.protein.

• Each gene has a locus, Each gene has a locus,

a specific position a specific position

on a pair of on a pair of

homologous chromosomeshomologous chromosomes


• For shape, there is a For shape, there is a wrinkled allele and a wrinkled allele and a round allele. They round allele. They receive one allele from receive one allele from each parent.each parent.

An allele is an alternative form of a geneAn allele is an alternative form of a gene--Each parent donates one allele for every Each parent donates one allele for every genegene


GenotypeGenotype

• Homozygous (pure)Homozygous (pure)• when both letters are the samewhen both letters are the same• ex: TT, ttex: TT, tt

• Heterozygous (hybrid)Heterozygous (hybrid)• when letters are differentwhen letters are different• always write the big letter firstalways write the big letter first• ex: Tt , Xx , Bbex: Tt , Xx , Bb

• Dominant Alleles are always upper case and Dominant Alleles are always upper case and recessive alleles are always lower case.recessive alleles are always lower case.


E. Mendel’s observed traitsE. Mendel’s observed traits

1.1. Rule of Dominance: When a Rule of Dominance: When a dominant trait is present the dominant trait is present the recessive trait is hiddenrecessive trait is hidden


Genes influence the development of traits.Genes influence the development of traits.

• All of an organism’s genetic All of an organism’s genetic material is called the genome.material is called the genome.

• A genotype refers to the actual A genotype refers to the actual genes.genes.

• A phenotype is the physical A phenotype is the physical expression of a trait.expression of a trait.


C. GenotypeC. Genotype::1. The gene combination of an 1. The gene combination of an

organismorganism

• It consists of 2 allelesIt consists of 2 alleles• For example:For example:

– PP PP

– PpPp

– pppp


Phenotype :The appearance. Phenotype :The appearance. • The genotype determines the phenotype.The genotype determines the phenotype.


Probability: The likelihood of an event.Probability: The likelihood of an event.

• A probability is expressed as a percentage or a A probability is expressed as a percentage or a fraction.fraction.

• Genotypic Ratio: The ratio of genotypes that will Genotypic Ratio: The ratio of genotypes that will appear.appear.

• Phenotypic Ratio: The ratio of phenotypes that will Phenotypic Ratio: The ratio of phenotypes that will appear. appear.

• We can find the probability of a certain genotype or We can find the probability of a certain genotype or phenotype by constructing a Punnett Square.phenotype by constructing a Punnett Square.


• When a dominant allele always gets its way (the When a dominant allele always gets its way (the dominant phenotype is present no matter its partner) dominant phenotype is present no matter its partner) it is called it is called COMPLETE DOMINANCE.COMPLETE DOMINANCE.– Example:Example:

Pp = Purple FlowerPp = Purple Flower

PP = Purple FlowerPP = Purple Flower

• Some times dominant traits don’t completely get Some times dominant traits don’t completely get their way……the alleles compromise. This results in their way……the alleles compromise. This results in a phenotype that is a mix of both parents. This is a phenotype that is a mix of both parents. This is called called INCOMPLETE DOMINANCE.INCOMPLETE DOMINANCE.– ExampleExample

Pp = light purple flowerPp = light purple flower


• In a few instances both alleles need to be expressed. In a few instances both alleles need to be expressed. This is called This is called Codominance.Codominance.

– ExampleExampleA mom chicken is black and dad chicken is white, but A mom chicken is black and dad chicken is white, but

the baby chick comes out black and white.the baby chick comes out black and white.


• Most traits occur Most traits occur in a range and do in a range and do not follow simple not follow simple dominant-dominant-recessive recessive patternspatterns

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