GeneticsGenetics

Dominant versus Recessive Dominant versus Recessive TraitsTraits

Dominant traits Dominant traits can mask or cover can mask or cover up others.up others.

Dominant traits are Dominant traits are represented by represented by capital letters. capital letters.

Recessive traits are Recessive traits are masked or covered masked or covered up.up.

Recessive traits are Recessive traits are represented by represented by lower-case letters.lower-case letters.

Mendel’s PrinciplesMendel’s Principles Heredity is not blending- there are discrete Heredity is not blending- there are discrete

dominant and recessive traits.dominant and recessive traits. There are units or particles of heredity- we know There are units or particles of heredity- we know

now that these are genes.now that these are genes. Every individual has a pair of these units for Every individual has a pair of these units for

every trait- we have 2 alleles for every trait.every trait- we have 2 alleles for every trait. These pairs separate in gametes- this happens These pairs separate in gametes- this happens

during meiosis where one homologue goes to during meiosis where one homologue goes to each daughter cell.each daughter cell.

Each gamete receives only one unit from each Each gamete receives only one unit from each pair- they are haploid and combine to become pair- they are haploid and combine to become diploid.diploid.

AllelesAlleles

Homozygous versus Homozygous versus HeterozygousHeterozygous

Homozygous Homozygous means that both means that both alleles are the alleles are the same thus both same thus both letters are the letters are the same.same.

The letters may be The letters may be either both capital either both capital or both lower-case. or both lower-case.

Heterozygous Heterozygous means that the means that the alleles are different alleles are different meaning that the meaning that the letters are letters are different.different.

One letter is capital One letter is capital and the other letter and the other letter is lower-case. is lower-case.

Genotype versus PhenotypeGenotype versus Phenotype

Heterozygous and Heterozygous and homozygous refer homozygous refer to your genotype.to your genotype.

Your genotype is Your genotype is what alleles you what alleles you have. have.

Phenotype only refers Phenotype only refers to what you look like. to what you look like.

Thus, if you show a Thus, if you show a dominant phenotype dominant phenotype you can be you can be heterozygous or heterozygous or homozygous dominant.homozygous dominant.

If you show the If you show the recessive phenotype, recessive phenotype, you must be you must be homozygous recessivehomozygous recessive..

To determine the To determine the phenotypes and phenotypes and

genotypes of genotypes of offspring,offspring,

You make a You make a Punnett Punnett Square!Square!

Unattached Earlobe

Dominant Phenotype

Attached Earlobe

Recessive Phenotype

Earlobe AttachmentEarlobe Attachment

Genotypic and Phenotypic Genotypic and Phenotypic RatiosRatios

Genotypic ratios Genotypic ratios express the results of express the results of the genotypes of the the genotypes of the offspring resulting offspring resulting from a Punnett from a Punnett Square. Square.

Therefore, they Therefore, they would state how would state how many offspring would many offspring would be homozygous and be homozygous and heterozygous. heterozygous.

Phenotypic ratios Phenotypic ratios express the results express the results of the phenotypes of the phenotypes of the offspring of the offspring resulting from a resulting from a Punnett Square.Punnett Square.

Therefore, they Therefore, they would state how would state how many of the many of the offspring would offspring would show a certain trait. show a certain trait.

Punnett Squares Show Punnett Squares Show Theoretical Ratios and Theoretical Ratios and

PercentagesPercentages

Recessive TraitsRecessive Traits

Tay-Sachs DiseaseTay-Sachs Disease Cystic FibrosisCystic Fibrosis PKUPKU

Dominant TraitsDominant Traits

Huntington DiseaseHuntington Disease HypercholesteroleHypercholesterole

miamia Marfan SyndromeMarfan Syndrome AchrondroplasiaAchrondroplasia

Non-Mendelian Non-Mendelian InheritanceInheritance

Polygenic InheritancePolygenic Inheritance

X

Yellow Lab

Black Lab

Chocolate Lab

Multiple AllelesMultiple Alleles

Co-DominanceCo-Dominance

Blood Type AllelesBlood Type Alleles

Blood Types and Blood Types and Paternity TestingPaternity Testing

This used to be all there was This used to be all there was and only allows you to and only allows you to

exclude someone as the exclude someone as the father, not to prove he is the father, not to prove he is the

father. Now we have DNA father. Now we have DNA fingerprinting!fingerprinting!

Sickle Cell Genotypes and Sickle Cell Genotypes and PhenotypesPhenotypes

HbHbAA Hb HbAA Normal Normal

HbHbAA Hb HbSS Sickle Cell Trait Sickle Cell Trait

HbHbSS Hb HbSS Sickle Cell Anemia Sickle Cell Anemia

Females Have 2 Copies of Females Have 2 Copies of the X the X

Chromosome, Males Only Chromosome, Males Only Have 1.Have 1.

The Male’s X Chromosome The Male’s X Chromosome Comes From His Mother.Comes From His Mother.

Since Males Have Only 1 Since Males Have Only 1 X Chromosome, They X Chromosome, They Will Show the Traits on Will Show the Traits on

that Chromosome.that Chromosome.

Sex Linked TraitsSex Linked Traits Men Cannot Be Carriers of a Sex-Linked Men Cannot Be Carriers of a Sex-Linked

TraitTrait

Sex Influenced TraitsSex Influenced Traits

Environmental InfluenceEnvironmental Influence