Step 2: Crossing the F1 generation Onetrait is dominant Onetrait is recessive Ratio of Dominant : recessive 12 purple: 4 white = 3 purple: 1 white
Interest Grabber continued Section 11-1 Mendel’s Results Parents (P) First Generation (F1) Second Generation (F2) Long stems × short stems All long 787 long: 277 short Red flowers × white flowers All red 705 red: 224 white Green pods × yellow pods All green 428 green: 152 yellow Round seeds × wrinkled seeds All round 5474 round: 1850 wrinkled Yellow seeds × green seeds All yellow 6022 yellow: 2001 greenGo toSection:
1. In the first generation of each experiment, how do the characteristics of the offspring compare to the parents’ characteristics? 2. How do the characteristics of the second generation compare to the characteristics of the first generation?
Using Diagrams to show inheritance: Punnett Squares Alleles= P P p p alternativ e forms of genesP = Pp P p purple p= white P p P p
Rules for Punnett Squares 1. Draw a square Place the traits for each parent across the top and side (alleles) Bring down the alleles from the top and across from the side Write the final ratio for the genotype & phenotype Add proper vocab terms (homozygous/heterozygous AND Dom & Recessive)
Perform the following cross from the F1 generation using a Punnett Square
Inheritance & Probability We have been examining inheritance using probablilty Probabilities predict AVERAGES! Not individuals. The offspring may not exactly match the predicted outcome (the larger the sample, the closer the expected values)
25% WW (homozygous dominant) 25% ww (homozygous recessive) 50% Ww (heterozygous) 75% White 25% Black Will it always turn out this way???
Two Factor/ Two Trait Crosses Law of Segregation Alleles separate from one another during meiosis Law of Independent Assortment Alleles segregate independently of one another (one does not depend on the other)
Two Trait Crosses Separatethe alleles using the FOIL method (kind of like a )R rYy RY Ry rY ryRrYy x RrYy
Phenotypic Ratio9 Yellow Round 3 Yellow wrinkled 3 green round 1 green wrinkled ALLHeterozygote two-trait crosses will result in a 9:3:3:1 ratio
Phenotypic Ratio for 2 trait crosses9 dominant dominant 3 dominant recessive 3 recessive dominant 1 recessive recessive
A Few Different Types of Inheritance http://www2.edc.org/weblabs/incompletedom/incomp
A New Kind of Inheritance Heterozygous phenotype is a blending of the recessive and dominant traits. What kind of inheritance? Incomplete Dom.
Codominance The dominant AND the recessive are both expressed RR x rr
Multiple Alleles Genes with more than two alleles. Ex: Rabbits C = full color; dominant to all other alleles Cch = chinchilla, partial defect in pigmentation, dominant to ch and c alleles ch Himilayan, color on certain parts of the body c= albino, no color
Codominant Cross Predictthe genotypic and phenotypic ratio of a cross between a Full Color Rabbit (Cch) and a himilayan (chc). Genotype:25% Cch, 25%Cc, 25% chch, chc Phenotype: 50% Full color, 50% himilayan
Sex-Linked Genes Even the X and Y chromosomes code for traits Since males only have one X chromosome, all traits are expressed… even the recessive! This explains why males are much more likely to develop Colorblindness Hemophilia Duchenne Muscular Dystrophy These are all genes on the X chromosome!
Sex Linked Cross XH YXH X X H H XH YXh XH Xh XhY
X-Inactivation How many X chromosomes do females have? How many X chromosomes do males have? Why do females need 2?