GENETICS. GENETICS TERMS Gene – section of chromosome that codes for a trait Gene – section of...

GENETICSGENETICS

GENETICS TERMSGENETICS TERMS GeneGene – section of chromosome that codes – section of chromosome that codes

for a traitfor a trait– Remember it’s the sequence of DNA nucleotides!Remember it’s the sequence of DNA nucleotides!

TraitTrait - a characteristic that varies from one - a characteristic that varies from one organism to the nextorganism to the next– Hair color, flower color, etc.Hair color, flower color, etc.

AlleleAllele - a different form of a gene - a different form of a gene – represented by lettersrepresented by letters

Different alleles:Different alleles:

Dominant alleleDominant allele – – alwaysalways expressed expressed when presentwhen present– UPPER CASE (Y for yellow peas)UPPER CASE (Y for yellow peas)

Recessive alleleRecessive allele - expressed - expressed onlyonly when the dominant allele is when the dominant allele is notnot presentpresent– lower case (y for green peas)lower case (y for green peas)

AlleleAllele

GENETICS TERMSGENETICS TERMS GenoGenotypetype - - genegenetic makeuptic makeup

– BB, Bb, bbBB, Bb, bb

PhPhenotypeenotype – – phphysical ysical characteristiccharacteristic– Green eyesGreen eyes– Brown hairBrown hair

GENOTYPESGENOTYPES HomoHomozygouszygous - two - two identicalidentical

alleles in a gene pair alleles in a gene pair (TT or tt)(TT or tt)

HeteroHeterozygouszygous - - differentdifferent alleles in a gene pair alleles in a gene pair (Tt) (Tt)

GENOTYPES GENOTYPES (cont’d)(cont’d)

Purebred or True BreedingPurebred or True Breeding - - organism that receives the organism that receives the samesame alleles from both of its parents alleles from both of its parents – Gene pair ex: BB or bbGene pair ex: BB or bb

HybridHybrid - organism that received - organism that received differentdifferent alleles from each parent alleles from each parent– Gene pairs ex: BbGene pairs ex: Bb

Chiweenie

Labradoodle

FertilizationFertilization – process of joining – process of joining male and female gametesmale and female gametes– Gametes are egg and sperm cellsGametes are egg and sperm cells

ExpressionExpression – when genes are – when genes are transcribed and translated into transcribed and translated into proteinsproteins

REVIEW FROM REVIEW FROM YESTERDAYYESTERDAY

•Allele for Widow’s Peak Allele for Widow’s Peak is dominantis dominant•A person with WW or A person with WW or Ww will have Widow’s Ww will have Widow’s PeakPeak

•Allele for Straight Hairline Allele for Straight Hairline is recessiveis recessive•A person with ww will A person with ww will have a Straight Hairlinehave a Straight Hairline

Genotype vs. PhenotypeGenotype vs. Phenotype

•Genotype refers to the allelesGenotype refers to the alleles

•Phenotype refers to the appearancePhenotype refers to the appearance

Example: Genotype - PhenotypeExample: Genotype - PhenotypeWW - person has a widow’s peakWW - person has a widow’s peakWw - person has a widow’s peakWw - person has a widow’s peakww - person has a straight hair lineww - person has a straight hair line

GREGOR MENDEL andGREGOR MENDEL andGENETICS LAWSGENETICS LAWS

GREGOR MENDEL GREGOR MENDEL (1822-1884)(1822-1884)

““Father of Genetics” Father of Genetics”

Scientist and MonkScientist and Monk

Worked with pea plants to Worked with pea plants to study how traits are passed study how traits are passed from one generation to nextfrom one generation to next

Why do you thinkWhy do you think scientists use rats, scientists use rats,

rabbits, insects, worms rabbits, insects, worms in laboratory in laboratory experiments?experiments?

Experiments such asExperiments such as-medicine-medicine

-studying genes-studying genes-genetic diseases-genetic diseases

Blast from the past:Blast from the past:

What characteristics What characteristics make a good make a good experiment?experiment?

Pea plants were used Pea plants were used because:because:

Visible traits that contrast Visible traits that contrast – tall tall OROR short; yellow short; yellow OROR green green

Produce large number of offspringProduce large number of offspring

Crosses (matings) can be controlled b/c Crosses (matings) can be controlled b/c of flower structureof flower structure

Scientist can isolate and control variables Scientist can isolate and control variables in laboratoryin laboratory

Repeatable experimentRepeatable experiment

Structure of Pea Structure of Pea FlowerFlower

Filament

Male Parts of Flowers

Anther

Female Parts of Flowers

Stigma

StyleOvary

Egg Petals

GENERATIONS: GENERATIONS: A – purple A – purple flowersflowers

a – white flowers a – white flowers 11stst cross = cross = Parental or P Parental or P

generationgeneration– Homozygous dominant and Homozygous dominant and

homozygous recessive – AA X aahomozygous recessive – AA X aa 11stst generation created= generation created= FF1 1

generationgeneration– Heterozygous – 100% AaHeterozygous – 100% Aa

AAAA aaaa

AaAa AaAa AaAa AaAa

Parental

22ndnd generation created (F generation created (F1 1 x Fx F11) = ) = FF22

– 1:2:1 genotypic ratio – 1 AA : 2 Aa : 1 1:2:1 genotypic ratio – 1 AA : 2 Aa : 1 aaaa

– 3:1 phenotypic ratio – 3 purple : 1 3:1 phenotypic ratio – 3 purple : 1 whitewhite

AaAa AaAa

AaAa AaAaAAAA aaaa

MENDEL’S LAWSMENDEL’S LAWS Law of SegregationLaw of Segregation - each gene - each gene

pair separates during meiosispair separates during meiosiseggegg egg egg

BB BB B B B B

**this states that sister chromatids **this states that sister chromatids must separatemust separate during Anaphase II** during Anaphase II**

MENDEL’S LAWSMENDEL’S LAWS Law of Independent AssortmentLaw of Independent Assortment

- gene pairs separate into gametes - gene pairs separate into gametes randomlyrandomly and and independentlyindependently of of each othereach other– Homologous chromosomes line up Homologous chromosomes line up

randomly and independently in randomly and independently in Metaphase IMetaphase I

EVERY POSSIBLE COMBINATION EVERY POSSIBLE COMBINATION HAS TO BE CONSIDEREDHAS TO BE CONSIDERED**this explains **this explains howhow sister chromatids sister chromatids

separate**separate**

Independent Assortment Independent Assortment when gametes are formedwhen gametes are formed

MENDEL’S LAWSMENDEL’S LAWS Law of DominanceLaw of Dominance – if the – if the

dominant allele is present in dominant allele is present in the gene pair, it is the gene pair, it is alwaysalways expressedexpressed– In other words, if you inherit a In other words, if you inherit a

dominant allele, you will always dominant allele, you will always show the dominant phenotypeshow the dominant phenotype

RANDOM RANDOM FERTILIZATIONFERTILIZATION

How many combos of human zygotes can How many combos of human zygotes can be formed? Remember – ovum + sperm be formed? Remember – ovum + sperm = Zygote= Zygote– 1 ovum = 8 million different chromosome 1 ovum = 8 million different chromosome

comboscombos– Fertilized by 1 sperm = 8 million different Fertilized by 1 sperm = 8 million different

comboscombos

= 64 trillion different combos for one zygote= 64 trillion different combos for one zygote

– 222323 x 2 x 22323 = over 70 trillion PLUS crossing over = over 70 trillion PLUS crossing over variations!variations!

X inactivationX inactivation

•Used on pregnant women over 35 years of ageUsed on pregnant women over 35 years of age•Performed during weeks 15-17 of pregnancyPerformed during weeks 15-17 of pregnancy•A needle is inserted into the amniotic sacA needle is inserted into the amniotic sac•Amniotic fluid with fetal cells is removedAmniotic fluid with fetal cells is removed•A karyotype of the fetal chromosomes is preparedA karyotype of the fetal chromosomes is prepared

Amniocentesis

Risk of Miscarriage

Risk of Down Syndrome

Risk of Having Child with Down Syndrome versus Risk of Miscarriage