GeneticsGenetics

Textbook Chapters 10-13Textbook Chapters 10-13

Review Book Topic 3Review Book Topic 3

Mendelian GeneticsMendelian Genetics 1866 – Gregor Mendel (Austrian monk)1866 – Gregor Mendel (Austrian monk)

Studied inheritance of traits in pea plantsStudied inheritance of traits in pea plants

•Easy to grow, breed, controlEasy to grow, breed, control

•““True breeding” – meaning they always True breeding” – meaning they always produce offspring with only one form of a produce offspring with only one form of a traittrait

Inheritance (heredity) – passing of traits Inheritance (heredity) – passing of traits onto onto the next generationthe next generation

Known as the “father of genetics”Known as the “father of genetics”

Noticed that certain Noticed that certain characteristics are characteristics are passed onto offspring passed onto offspring from generation to from generation to generation (traits)generation (traits)

Mendel controlled cross-Mendel controlled cross-pollination (breeding) pollination (breeding) between plants by between plants by removing the male removing the male organs from the flowerorgans from the flower

He then chose which He then chose which plants reproducedplants reproduced

Mendel called the Mendel called the parent plants the parent plants the ““P” generationP” generation

When crossing two When crossing two ““P” generation, the P” generation, the offspring produced offspring produced were called the “Fwere called the “F11” ” generation (hybrids)generation (hybrids)

By crossing two “FBy crossing two “F11” ” generation, Mendel generation, Mendel could study if could study if characteristics couldcharacteristics couldskip generationsskip generations

Creates the “FCreates the “F22” generation” generation

Mendel studied seven different traitsMendel studied seven different traits

Seed colorSeed color

Flower colorFlower color

Seed pod colorSeed pod color

Seed shape or Seed shape or texturetexture

Seed pod shapeSeed pod shape

Stem lengthStem length

Flower positionFlower position

After his experiments Mendel concluded:After his experiments Mendel concluded:

There must be two forms of a traitThere must be two forms of a trait

Each form is controlled by an alleleEach form is controlled by an allele

• Allele – alternate form of a single gene passed Allele – alternate form of a single gene passed on from generation to generationon from generation to generation

•Dominant allele (A) – form of the trait that Dominant allele (A) – form of the trait that appears in the Fappears in the F11 generation (shown) generation (shown)

o Doesn’t mean it is strongerDoesn’t mean it is stronger

or more present in the or more present in the

populationpopulation

Ex. PolydactylyEx. Polydactyly

•Recessive allele (a) – form of the trait that Recessive allele (a) – form of the trait that is masked in the Fis masked in the F11 generation (not shown) generation (not shown)

Traits are different forms of a single Traits are different forms of a single genegene

•Genes contain a segments of DNA Genes contain a segments of DNA which codes for a specific proteinwhich codes for a specific protein

Law of SegregationLaw of Segregation

Homologous traits occur in pairs on homologous Homologous traits occur in pairs on homologous

chromosomeschromosomes

Separated from each other during gamete Separated from each other during gamete

formation (Law of Independent Assortment)formation (Law of Independent Assortment)

Recombine at fertilizationRecombine at fertilization

One form of a trait is inherited from each parentOne form of a trait is inherited from each parent

Law of DominanceLaw of Dominance

Homozygous – an organism with two of Homozygous – an organism with two of the the samesame alleles for a given trait (AA, aa) alleles for a given trait (AA, aa)

Heterozygous – an organism with two Heterozygous – an organism with two differentdifferent alleles for a given trait (Aa) alleles for a given trait (Aa)

• When heterozygous, the dominant trait will be When heterozygous, the dominant trait will be observedobserved

Three forms of dominance:Three forms of dominance:

•Homozygous dominant – AAHomozygous dominant – AA

•Heterozygous – AaHeterozygous – Aa

•Homozygous recessive – aaHomozygous recessive – aa

CharacteristicsCharacteristics

The outward appearance does not The outward appearance does not always always indicate which pair of alleles is presentindicate which pair of alleles is present

Genotype – organism’s allele pairs (AA, Genotype – organism’s allele pairs (AA, Aa, aa)Aa, aa)

Phenotype – observable characteristic of Phenotype – observable characteristic of an allele pair (tall, short, green, yellow)an allele pair (tall, short, green, yellow)

It is possible for two organisms to have It is possible for two organisms to have the the

same phenotype but different genotypessame phenotype but different genotypes

The genotype and phenotype of an The genotype and phenotype of an

organism is called a genomeorganism is called a genome

Activity #1Activity #1

Genotype versus phenotype smiley Genotype versus phenotype smiley face activityface activity

Punnett Squares (1900s)Punnett Squares (1900s)

Used to predict the possible offspring of a Used to predict the possible offspring of a

cross between two known genotypescross between two known genotypes

•Each parent contributes one allele per Each parent contributes one allele per square in the boxsquare in the box

Monohybrid cross – only the inheritance of Monohybrid cross – only the inheritance of one one trait is being studiedtrait is being studied

•Homozygous-homozygous Homozygous-homozygous o AA x AAAA x AAo AA x aaAA x aao aa x aaaa x aa

•Homozygous-heterozygousHomozygous-heterozygouso AA x Aa AA x Aa o aa x Aaaa x Aa

•Heterozygous-heterozygousHeterozygous-heterozygouso Aa x AaAa x Aa

Dihybrid cross – inheritance of two or Dihybrid cross – inheritance of two or

more different traits are being studiedmore different traits are being studied

Test CrossTest Cross

•An individual of unknown genotype is mated An individual of unknown genotype is mated with an individual showing the homozygous with an individual showing the homozygous recessive traitrecessive trait

o Unknown could be homozygous or Unknown could be homozygous or heterozygousheterozygous

o Look at offspring produced to determine Look at offspring produced to determine unknown genotypeunknown genotype

Law of Independent AssortmentLaw of Independent Assortment

Allele pairs are randomly separatedAllele pairs are randomly separated

independently during gamete formation independently during gamete formation (meiosis)(meiosis)

Different traits are inherited separatelyDifferent traits are inherited separately

Exception is gene linkageException is gene linkage

•Linked genes are inherited togetherLinked genes are inherited together

Activity #2Activity #2

Punnett square practice worksheetPunnett square practice worksheet

Law of ProbabilityLaw of Probability

“ “Law of chance”Law of chance”

Inheritance of genes Inheritance of genes can be compared to can be compared to flipping a coinflipping a coin

Probability = Probability = # of ways a specific event can occur# of ways a specific event can occur # of total possible outcomes# of total possible outcomes

Activity #3Activity #3

Probability and Inheritance LabProbability and Inheritance Lab

Heredity BrainPop

Exceptions to Mendel’s Exceptions to Mendel’s LawsLaws Incomplete dominanceIncomplete dominance

Both alleles contribute to the phenotype Both alleles contribute to the phenotype

Heterozygote is an intermediate of two Heterozygote is an intermediate of two parent’s traitsparent’s traits

CodominanceCodominance

No single allele is No single allele is

dominantdominant

Both alleles expressed Both alleles expressed

at same timeat same time

Polygenic InheritancePolygenic Inheritance

More than one gene can affect a single More than one gene can affect a single traittrait

• Ex. Four genes are involved in eye colorEx. Four genes are involved in eye color• Ex. Human heightEx. Human height• Ex. Skin colorEx. Skin color

PleiotrophyPleiotrophy

A single gene can affect more than one A single gene can affect more than one

traittrait

• Ex. Cystic fibrosis, sickle cell anemiaEx. Cystic fibrosis, sickle cell anemia

Gene Interactions (epistasis)Gene Interactions (epistasis)

Products of genes Products of genes

(proteins) can (proteins) can

interact to alter interact to alter

genetic ratiosgenetic ratios

• Ex. Coat color in Ex. Coat color in

mammalsmammals

• Ex. Purple pigment Ex. Purple pigment

in cornin corn

Environmental EffectsEnvironmental Effects

Genes may be Genes may be

affected by the affected by the

environmentenvironment

• Ex. coat color in arctic Ex. coat color in arctic

fox or hares (rabbits)fox or hares (rabbits)

• Ex. Siamese catsEx. Siamese cats

Multiple alleles for one gene

Genes may have more than two alleles

• Ex. blood type

o A, B, O alleleso Types: A, B, AB, Oo IAIA / IAi (A); IBIB / IBi (B); IAIB (AB); ii

(O)

PedigreesPedigrees

Diagram that shows the phenotypes of several Diagram that shows the phenotypes of several generations in a family tree for a specific traitgenerations in a family tree for a specific trait

Symbols used:Symbols used:

Female - Female -

Male – Male –

Shading indicates individual shows the traitShading indicates individual shows the trait

Marriage represented by horizontal line between Marriage represented by horizontal line between

Offspring represented by vertical linesOffspring represented by vertical lines

Applied GeneticsApplied Genetics Selective BreedingSelective Breeding

Humans breed animals/plants with certain Humans breed animals/plants with certain

traits to obtain offspring that have desired traits to obtain offspring that have desired traitstraits

Results in traits becoming more Results in traits becoming more

common in a breedcommon in a breed

                                                    

     

HybridizationHybridization

Animals/plants are bred to form Animals/plants are bred to form heterozygotesheterozygotes

Heterozygous advantageHeterozygous advantage• Ex. Disease resistance, increased offspring Ex. Disease resistance, increased offspring

variation, faster growth, higher fruit yieldvariation, faster growth, higher fruit yield

Disadvantages:Disadvantages:• Time consumingTime consuming• ExpensiveExpensive• Careful selection of parents to produce correct Careful selection of parents to produce correct

combinations of traits in offspringcombinations of traits in offspring

InbreedingInbreeding

Two closely related organisms are bred toTwo closely related organisms are bred to

have the desired traitshave the desired traits

Also to eliminate the undesired traits in futureAlso to eliminate the undesired traits in future

generationgeneration

Disadvantage – harmful recessive traits alsoDisadvantage – harmful recessive traits also

can be passed on to future generations in can be passed on to future generations in

homozygous recessive individualshomozygous recessive individuals

Examples of Human InbreedingExamples of Human InbreedingAncient EgyptAncient Egypt

• Pharaohs married their sistersPharaohs married their sisters

Royal EuropeRoyal Europe• Royalty married within their familyRoyalty married within their family