Chapter 13.4 Probability and Genetics

Computer Karyotypes(new) Now we know enough about chromosomes Dyes specific to certain chromosomes –Bind to spec Different colors Computers can sort them into karyotype

Example of chromosomal disorder Down’s Syndrome –Extra chromosome # 21 –Learning difficulties

Diploid Organims Two of every chromosome One from mom, one from dad Both have same gene(ex. Eye color) Both may have different forms(alleles)

Probability Mathematics The chance that a certain event will happen –33% chance of rain –50% chance of having a baby boy –Flipping a coin, how many outcomes?

How many outcomes? 2 outcomes: What is the chance of flipping tails?

1/2 Probability expressed as fraction (number of desired trait)/(all possible outcomes) If you toss a coin ten times, how many tails do you think you will get?

Prediction: 5 Tails # of Trials x probability = prediction Ex. 10 x ½ = 5 Tails

Genetics use Probability Gender How many outcomes? Chance of having a boy? If you have four children, how many boys do you predict?

Two Laws Affecting Probability Previous events don’t affect one event –If you have five girls already, you still have the ½ chance of having a girl You can predict the possibility of having three girls or three head tosses in a row. –(1/2) x (1/2) x (1/2)= 1/8

Probability works best Constant environment –No varying factors Large sample size One outcome does not have advantage than any other outcome

Monohybrid Cross Mendel studied plants Monohybrid=refers to only differing in one trait Cross=mate, reproduce

Pgen= parental generation –Plants involved in initial cross

F1 generation: First Filial generation F1: all green pods

F2:Second Filial Generation Roughly a 3 green:1 yellow ratio

Alleles(different forms of gene) Gene: pod color –Allele: green vs yellow Dominant allele Recessive allele –Is hidden when dominant is present We use letters to represent a gene and capitals to represent the dominant form –G= green pods g= yellow pods

You are diploid Two pairs of chromosomes=two alleles for each gene Homozygous: –Have two same alleles,GG or gg –True-breeding organisms Heterozygous: –Different alleles for a gene, Gg –Dominant gene is seen over recessive

Genotype: –Genetic makeup –What two alleles you have –Ex. GG is a genotype Phenotype: –Physical trait –What can be seen –Ex. Green pods are the phenotype

Mendel’s Principles Principle of Segregation Principle of Independent Assortment

Principle of Segregation You have two alleles Meiosis takes one cell and divides into four gametes –A plant cell with –Cell cycle replicates chromosomes –Meiosis separates into four gametes Gg GGgg g G G g

Any one of those gametes can mate with the gametes of another organism g G G g g G G g Genotype: Gg Phenotype: green pods

Punnett Squares Used to predict offspring of 2 organisms Step 1: Draw a punnett square –One box divided into four quandrants

Punnett Squares Step 2: Determine the possible genotypes of both parents –If there is more than one possibility, do more one punnet square for each –Ex. Tall plant(Tt) with short plant(tt) Step 3: Take one parent and split genotype up on and split genotype up on left side left side

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

Punnett Squares

Step 5: Write down all possible genotypes in ratio form Step 5: Write down all possible genotypes in ratio form Ex. 1 2 Tt: 2 tt simplify ratio 1 Tt: 1 tt

Step 6: Write down all possible phenotypes in ratio form Step 6: Write down all possible phenotypes in ratio form Ex. 1 1 Tall plant: 1 Short plant