FundamentalFundamentals of Geneticss of Genetics

CHAPTER

9

Patterns of InheritancePatterns of Inheritance

The History of GeneticsThe History of Genetics GeneticsGenetics – scientific study of heredity – scientific study of heredity TraitTrait – characteristic that can be – characteristic that can be

passed from parents to offspringpassed from parents to offspring

Father of GeneticsFather of Genetics Gregor Mendel Gregor Mendel

(born 1822)(born 1822)Austrian Monk Austrian Monk Studied 7 Studied 7

different pea different pea plant traits that plant traits that are are true-true-breedingbreeding Produce offspring Produce offspring identical to identical to themselvesthemselveshttps://www.youtube.com/watch?v=GTiOETaZg4w

Parental CrossParental CrossCross-pollinated flowers with Cross-pollinated flowers with

opposite traits (tall, short) opposite traits (tall, short) P generationP generation

Plants from the first cross Plants from the first cross were all tall- were all tall- hybridshybrids. . FF11 generation generation

FF11 Cross Cross Allowed f1 plants to self-Allowed f1 plants to self-

fertilizefertilize The recessive trait had The recessive trait had

reappeared!!reappeared!! About 25% of the offspring About 25% of the offspring

(F(F22 generation) were short. generation) were short.

Mendel’s Mendel’s ConclusionsConclusions 1. Biological inheritance is passed from one 1. Biological inheritance is passed from one

generation to the next- generation to the next- GenesGenes AllelesAlleles- different forms of a gene- different forms of a gene

2. Some alleles are 2. Some alleles are dominantdominant Capital Letter -R,DCapital Letter -R,D Some alleles are Some alleles are recessiverecessive Lowercase letters – r, d Lowercase letters – r, d

3. 3. Principle of SegregationPrinciple of Segregation Alleles separate from each other during formation of sex Alleles separate from each other during formation of sex

cells, or cells, or gametesgametes..https://www.youtube.com/watch?v=Mehz7tCxjSE

Genes Represent TraitsGenes Represent Traits GenotypeGenotype – genes that make up an organism – genes that make up an organism

Includes both genes in a homologous pairIncludes both genes in a homologous pair

PhenotypePhenotype – outward expression of the trait – outward expression of the trait

HomozygousHomozygous – two alleles are identical (AA or aa) – two alleles are identical (AA or aa)

HeterozygousHeterozygous – two alleles are different (Aa) – two alleles are different (Aa)

Also known as a hybrid organismAlso known as a hybrid organism

PurebredPurebred – organism receives the same genetic – organism receives the same genetic traits form both of its parentstraits form both of its parents HomozygousHomozygous – AA or aa – AA or aa

HybridHybrid – organism receives different forms of a – organism receives different forms of a genetic traitgenetic trait HeterozygousHeterozygous - Aa - Aa

Important TermsImportant Terms

GenesGenes – sections of a chromosome that – sections of a chromosome that code for a traitcode for a trait

AlleleAllele – distinct form of a gene – distinct form of a gene Dominant AlleleDominant Allele – expressed when two – expressed when two

different alleles are present; represented different alleles are present; represented with capital letterwith capital letter

Recessive AlleleRecessive Allele – form of gene that is not – form of gene that is not expressed when paired with a dominant expressed when paired with a dominant allele; represented with lower case letterallele; represented with lower case letter

Genetics and Genetics and PredictionPrediction

Predictions for One TraitPredictions for One Trait

ProbabilityProbability – predict likelihood of an – predict likelihood of an event or outcomeevent or outcome

Punnett squarePunnett square – grid for organizing – grid for organizing genetic informationgenetic information Can be used to make predictions about Can be used to make predictions about

a cross between two organsimsa cross between two organsims Monohybrid CrossMonohybrid Cross – cross between two – cross between two

parents and one traitparents and one trait

Monohybrid CrossMonohybrid Cross

Predictions for Two Predictions for Two TraitsTraits

Dihybrid CrossDihybrid Cross – cross between – cross between

two parents and two traitstwo parents and two traits Use a 4 x 4 Use a 4 x 4

Punnett squarePunnett square Sixteen possible outcomesSixteen possible outcomes

Incomplete DominanceIncomplete Dominance

Heterozygous offspring show a Heterozygous offspring show a phenotype that is in-between the phenotype that is in-between the phenotypes of the two homozygous phenotypes of the two homozygous parentsparents Blending of traitsBlending of traits Color in snapdragons; Color in snapdragons;

instead of white or red, instead of white or red,

color is pinkcolor is pink

CodominanceCodominance

Both alleles are expressed Both alleles are expressed Example: Blood typeExample: Blood type

IIAA, I, IBB, i(O), or I, i(O), or IAAIIBB blood type blood type Both A and B are dominant so they are Both A and B are dominant so they are

both expressed in the Iboth expressed in the IAAIIBB blood type blood type

Polygenic TraitPolygenic Trait

Trait controlled by more than Trait controlled by more than one geneone gene Example: eye colorExample: eye color

https://www.youtube.com/watch?v=CBezq1fFUEA