Mendelian Genetics Learning Goal: How are traits passed down from parents to offspring? Concept 1 : Analyzing the effects of classic Mendelian genetic crosses such as monohybrid, dihybrid, testcross, and applying to pedigree diagrams. PART 2

Try This!  An organism with the genotype AaBb is crossed with an organism that has the genotype AABb.  What are all the possible gametes of each individual parent?  What is the probability that any of the offspring has the AABB genotype?  If A and B exhibit complete dominance, what is the probability of the offspring exhibiting both the A and B phenotypes?

Try This!  An organism with the genotype AaBb is crossed with an organism that has the genotype AABb.  What are all the possible gametes of each individual parent? AaBb x AABb AB AB Ab Ab aB ab  What is the probability that any of the offspring has the AABB genotype? AABB – 2 punnet squares! AA: ½ BB: ¼ ½ x ¼ = 1/8  If A and B exhibit complete dominance, what is the probability of the offspring exhibiting both the A and B phenotypes? What genotypes give dominance for A and B? A_B_ A_: 1 B_: ¾ 1 x ¾ = 3/4 AA AAA aAa Bb BBBBb b bb

Concept 1 : Analyzing the effects of classic Mendelian genetic crosses such as monohybrid, dihybrid, testcross, and applying to pedigree diagrams.  Terms associated with genetics problems: P, F 1, F 2, dominant, recessive, homozygous, heterozygous, phenotypic, and genotypic  How to derive the proper gametes, genotypes, and phenotypes, when working a genetics problem (monohybrid, dihybrid, testcross)  The difference between an allele and a gene  How to read a pedigree (monohybrid, dihybrid, testcross)

Make Math Work for YOU!  Rule of Multiplication :  Independent events happening at the same time  “this and that together”  Example: three coins are flipped. The probability that all three coins show tails is  ½ x ½ x ½ = 1/8

Make Math Work for YOU!  Rule of Addition  Mutually exclusive events  “this or that” “different ways of getting the same thing”  Example: three coins are flipped. What is the probability of getting one tail and two heads?  - tail, head, head 1/8 (½ x ½ x ½ rule of multiplication)  - head, head, tail 1/8  - head, tail, head 1/8  The probability that two coins are heads and one is tail is: 1/8 + 1/8 + 1/8 = 3/8

Tips for working through genetics problems:  THERE IS NO MAGICAL FORMULA!!!!  What do you HAVE ?  What do you WANT ?  Plan a way to get there using a combination of:  punnet squares  probabilities  logic

Try This!  In peas, yellow seed colour is dominant over green seed colour, and round seed shape is dominant over wrinkled seed shape.  A round-yellow seeded plant was crossed with a green-wrinkled seeded plant producing 20 plants: 11 of these plants has yellow-round seeds, and 9 of these plants had green-round seeds.  What was the probable genotypes of the parent plants?

Tips for working through genetics problems:  Write down the allele symbols using the same letter for a gene:  upper case for dominant (ex: Yellow – Y)  lower case for recessive (ex: green – y).  Write down the phenotypes for each individual.

Tips for working through genetics problems:  Write down possible genotypes for each individual.  If the phenotype is recessive, genotype must be homozygous recessive (green = yy)  If the phenotype is dominant, genotype is either homozygous dominant or heterozygous. (yellow = YY or Yy, can write Y_)  If the phenotype is “true-breeding,” the genotype is homozygous for that trait.

Tips for working through genetics problems:  Write down what you are looking for in the question.  If you need to find genotype/phenotypes of offspring (or “grandchildren”), complete the cross (Yy x yy) and use the probability rules or the Punnet square.  If you need to find genotypes/phenotypes of parents or (or “grandparents”), deduce by working backwards and reasoning. (Note: numbers of offspring may be actual rather than predicted by ratios… 1:1 ratio may be 13 individuals:15 individuals)

Shortcuts!  3:1 ratio indicates a monohybrid cross (Aa x Aa)  1:1 ratio indicates a cross of a heterozygote with a homozygous recessive (Aa x aa)  All offspring identical to parents suggests a cross of parents that are homozygous for the same trait, or homozygous dominant with heterozygous (AA x AA or aa x aa or AA x Aa)  9:3:3:1 ratio indicates a dihybrid cross (AaBb x AaBb)  1:1:1:1 ratio indicates a cross of a dihybrid with a double homozygous recessive (AaBb x aabb)

We just need to practice…  Try… On Worksheets: Multiple Choice: 1, 2, 3, 5, 7, 8, 10, 13 Genetics Problems: 1, 2, 6, 12, 13

Pedigrees…