Chapter 13.4Chapter 13.4

Probability and GeneticsProbability and Genetics

Computer Karyotypes(new)Computer Karyotypes(new)Now we know Now we know enough about enough about chromosomeschromosomesDyes specific to Dyes specific to certain certain chromosomeschromosomes– Bind to specBind to spec

Different colorsDifferent colorsComputers can sort Computers can sort them into them into karyotypekaryotype

Example of chromosomal disorderExample of chromosomal disorder

Down’s SyndromeDown’s Syndrome– Extra chromosome Extra chromosome

# 21# 21– Learning difficultiesLearning difficulties

Diploid OrganimsDiploid OrganimsTwo of every chromosomeTwo of every chromosome

One from mom, one from dadOne from mom, one from dad

Both have same gene(ex. Eye color)Both have same gene(ex. Eye color)

Both may have different forms(alleles)Both may have different forms(alleles)

ProbabilityProbabilityMathematicsMathematics

The chance that a certain event will The chance that a certain event will happenhappen– 33% chance of rain33% chance of rain– 50% chance of having a baby boy50% chance of having a baby boy– Flipping a coin, how many outcomes?Flipping a coin, how many outcomes?

How many outcomes?How many outcomes?2 outcomes:2 outcomes:

What is the chance of flipping tails?What is the chance of flipping tails?

1/21/2Probability expressed as fractionProbability expressed as fraction

(number of desired trait)/(all possible (number of desired trait)/(all possible outcomes)outcomes)

If you toss a coin ten times, how many tails do you think you will get?

Prediction: 5 TailsPrediction: 5 Tails# of Trials# of Trials x x probability probability = prediction = prediction

Ex. Ex. 1010 x x ½ ½ = = 5 Tails 5 Tails

Genetics use ProbabilityGenetics use Probability

GenderGender

How many outcomes?How many outcomes?

Chance of having a boy?Chance of having a boy?

If you have four children, how many If you have four children, how many boys do you predict?boys do you predict?

Two Laws Affecting ProbabilityTwo Laws Affecting Probability

Previous events don’t affect one Previous events don’t affect one eventevent– If you have five girls already, you still If you have five girls already, you still

have the ½ chance of having a girlhave the ½ chance of having a girl

You can predict the possibility of You can predict the possibility of having three girls or three head having three girls or three head tosses in a row.tosses in a row.– (1/2) x (1/2) x (1/2)= 1/8(1/2) x (1/2) x (1/2)= 1/8

Probability works bestProbability works best

Constant environmentConstant environment– No varying factorsNo varying factors

Large sample sizeLarge sample size

One outcome does not have One outcome does not have advantage than any other outcomeadvantage than any other outcome

Monohybrid CrossMonohybrid CrossMendel studied plants Mendel studied plants

Monohybrid=refers to only differing in Monohybrid=refers to only differing in one traitone trait

Cross=mate, reproduceCross=mate, reproduce

PgenPgen= parental generation= parental generation– Plants involved in initial crossPlants involved in initial cross

F1 generation: First Filial F1 generation: First Filial generationgeneration

F1: all green podsF1: all green pods

F2:Second Filial GenerationF2:Second Filial GenerationRoughly a 3 green:1 yellow ratioRoughly a 3 green:1 yellow ratio

Alleles(different forms of gene)Alleles(different forms of gene)Gene: pod colorGene: pod color– Allele: green vs yellowAllele: green vs yellow

Dominant alleleDominant alleleRecessive alleleRecessive allele– Is hidden when dominant is presentIs hidden when dominant is present

We use letters to represent a gene We use letters to represent a gene and capitals to represent the and capitals to represent the dominant formdominant form– G= green pods g= yellow podsG= green pods g= yellow pods

You are diploid You are diploid

Two pairs of chromosomes=two Two pairs of chromosomes=two alleles for each genealleles for each gene

HomozygouHomozygous:s:– Have two same alleles,GG or ggHave two same alleles,GG or gg– True-breeding organismsTrue-breeding organisms

Heterozygous:Heterozygous:– Different alleles for a gene, GgDifferent alleles for a gene, Gg– Dominant gene is seen over recessiveDominant gene is seen over recessive

Genotype:Genotype:– Genetic makeupGenetic makeup– What two alleles you haveWhat two alleles you have– Ex. GG is a genotypeEx. GG is a genotype

Phenotype:Phenotype:– Physical traitPhysical trait– What can be seenWhat can be seen– Ex. Green pods are the phenotype Ex. Green pods are the phenotype

Mendel’s PrinciplesMendel’s Principles

Principle of SegregationPrinciple of Segregation

Principle of Independent AssortmentPrinciple of Independent Assortment

Principle of SegregationPrinciple of SegregationYou have two You have two allelesallelesMeiosis takes one Meiosis takes one cell and divides into cell and divides into four gametesfour gametes– A plant cell with A plant cell with – Cell cycle replicates Cell cycle replicates

chromosomeschromosomes– Meiosis separates Meiosis separates

into four gametesinto four gametes

Gg

GGgg

g

G

G

g

Any one of those gametes can mate with the Any one of those gametes can mate with the gametes of another organismgametes of another organism

g

G

G

g

g

G

G

g

Genotype: Gg

Phenotype: green pods

Punnett SquaresPunnett SquaresUsed to predict Used to predict offspring of 2 offspring of 2 organismsorganisms

Step 1: Draw a Step 1: Draw a punnett squarepunnett square– One box divided One box divided

into four into four quandrantsquandrants

Punnett SquaresPunnett SquaresStep 2: Determine the possible genotypes Step 2: Determine the possible genotypes of both parentsof both parents– If there is more than one possibility, do more If there is more than one possibility, do more

one punnet square for eachone punnet square for each– Ex. Tall plant(Tt) with short plant(tt)Ex. Tall plant(Tt) with short plant(tt)

Step 3: Take one parentStep 3: Take one parent

and split genotype up onand split genotype up on

left sideleft side

Punnett SquaresPunnett SquaresStep 4: Take genotype of other parents and Step 4: Take genotype of other parents and split it up over top of squaresplit it up over top of square

Punnett SquaresPunnett Squares

Step 5: Write down all possible Step 5: Write down all possible genotypes genotypes in ratio form in ratio form

Ex. 1 2 Tt: 2 ttEx. 1 2 Tt: 2 tt

simplify ratio 1 Tt: 1 ttsimplify ratio 1 Tt: 1 tt

Step 6: Write down all possible Step 6: Write down all possible phenotypes in ratio formphenotypes in ratio form

Ex. 1 1 Tall plant: 1 Short plantEx. 1 1 Tall plant: 1 Short plant