Mendel s Principle of Segregation:

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1 What is heredity? What is a trait? What is an allele? Key Terms to Know! phenotype genotype homozygous heterozygous hybrid dominant recessive Punnett square monohybrid cross dihybrid cross Mendel s Principle of Segregation: Alleles separate in meiosis, then come back together in the zygote (offspring) through Fertilization Parents = P generation Offspring = F 1 generation Their offspring = F 2 generation What was the PHENOTYPE of F 1 hybrid plants like? Which parent did they resemble? What about the F 2? 1

2 Explain: MENDEL S CONCLUSIONS 1. Inheritance is determined by what he called factors. What are these? 2. The Principal of Dominance means: 3. Did the recessive allele disappear in the F 1 plants? 4. How could he test this? The F 1 Cross: Phenotypes: Genotypes: Define the Principal of SEGREGATION: 2

3 Explaining the F1 Cross Mendel s Hypotheses 1. There are alternative forms of genes called. 2. How many alleles does an organism have for each gene? 3. If the alleles are the SAME, the individual is for that trait. 4. If the alleles are DIFFERENT, the individual is or a for that trait. 5. In a heterozygous individual the allele that appears in the Phenotype is called the allele (P) 6. The other allele that does not appear called the allele. (p) 7. The two alleles for a trait segregate (separate) during the formation of (sex cells), so that each carries only one allele for each characteristic. 8. This is known as Mendel s 9. The joining of gametes during reforms allele pairs in the offspring. 10. By what process that we studied do alleles SEGREGATE? 11. What types of cells are produced as a result? (haploid/diploid? Why does it matter?) 12. How many copies of an allele does an offspring inherit from the male parent? 13. How many copies of an allele does an offspring inherit from the female parent? 14. An observable trait (such as purple flowers) is called the 15. The genetic makeup, or combination of alleles (such as PP), is called the Punnett Square Shows all possible outcomes of a genetic cross. Used to predict probabilities of types of offspring if you know the genetic makeup (genotype) of both parents. How is a Punnett Square an abbreviation of Meiosis (gametes) and Fertilization (Zygotes)? Cross two parents that are both Heterozygous for free earlobes. Aa x Aa (Monohybrid Cross) Allele Key: A = Free earlobe a = attached earlobe Parent #1 Gametes RESULTS: (Ratio or Percentages) Parent #2 Gametes A A F 1 Offspring a F 1 Offspring a F 1 Offspring F 1 Offspring 1. Phenotype: # Free earlobe # Attached earlobe 2. Genotype: # Homozygous Dominant # Heterozygous # Homozygous Recessive 3

4 Monohybrid Practice Problems: 1. In pea plants, round peas are dominant over wrinkled peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between a plant homozygous for round peas (RR) and a plant homozygous for wrinkled peas (rr). 2. Jake s second toe is much longer than his thumb toe at least an inch! This is a recessive trait. If he marries Charlotte, who is a heterozygous for having her second toe shorter than her thumb toe, answer the following questions. Use the letter T to represent this allele. a. Which trait is dominant long second toe or short second toe? b. What are Jake s and Charlotte s genotypes? c. If Jake s and Charlotte s have children, what are the possibilities of their children s phenotype? d. What are the possibilities of their children s genotype? 3. Alex is so double jointed that his thumb can bend over backwards to touch his watch. His father is double jointed also, but his mother is not. If being double jointed is a recessive trait, what is the genotype of Alex and his parents? Use the letter D to represent the allele for this trait. Mendel s Principle of Independent Assortment Define Independent Assortment: Define DiHybrid Cross: Trait #1 Trait #2 Dominant = Round shape Recessive = Wrinkled shape Dominant = Yellow Recessive = Green ***Alleles for different traits are located on different Homologous Chromosome Paris, therefore they assort and separate during Meiosis INDEPENDENTLY from each other!**** 4

5 The Dihybrid Cross Round & Yellow Pea Plant (RRYY) (Parent #1) Wrinkled & Green Pea Plant (rryy) (Parent #2) x What gametes would these two Parents produce? In other words, how will the alleles for these two traits segregate (Pull apart in meiosis)? (Parent #1) RRYY: (Parent #2) rryy: Set up the Punnett Square to Cross these parents: (Notice this Punnett Square has only one box for offspring. That s because each parent above only made kind of gamete, so only one kind of offspring is possible) Parent #1 Gametes RESULTS: Phenotype of all F 1 offspring: Parent #2 Gametes Offspring Genotype of all F 1 offspring: 5

6 Before we Cross the two Dihybrids, let s look at: Independent Assortment of Alleles during Meiosis F 1 Geneotype = RrYy R= Round r = wrinkled Y = Yellow y = green In Possibility #1: The Paternal Chromosomes RANDOMLY lined up one on top of the other during Metaphase I ending up together in the Haploid gametes R and Y ended up together r and y ended up together In Possibility #2: One Paternal Chromosome RANDOMLY Lined up above one Maternal Chromosome (and vice versa), creating Haploid gametes that were a mixture of paternal and maternal alleles. R and y ended up together r and Y ended up together What are the four different allele combinations the F 1 parent can make in its gametes? These are the four different allele combinations that are ALWAYS made in a Dihybrid s gametes! Now we are ready to Cross the two Dihybrids! (RrYy x RrYy) 6

7 The DiHybrid Cross: F 1 This is a Dihybrid Cross: Crossing two organisms that are hybrid for Two Traits! RrYy x RrYy 1. What types of GAMETES can these Parents produce, assuming that the alleles segregate independently? (**Hint: Principle of Independent Assortment: Genes for different Traits segregated independently during the formation of gametes) 2. Set up the Punnet Square place the alleles for the gametes of one parent across the top and the alleles for the other parent down the side. 3. Fill in the possible offspring types. Gametes Parent #1 Gametes Parent #2 4. How many offspring of the 16 possibilities are: a. Yellow and Round (Dominant/Dominant) b. Yellow and Wrinkled (Dominant/ Recessive) c. Green and Round (Dominant /Recessive) d. Green and Wrinkled (Recessive/Recessive) 5. Summarize Mendel s Principle of Independent Assortment: 6. What would the probability have been of producing a Yellow Wrinkled offspring if the parents had been RRYY x rryy? 7

8 Dihybrid Practice Problems: 1) For eye color, brown B is the dominant allele, and blue b is the recessive allele. For the shape of the nose, pointy P is the dominant allele, and flat p is the recessive allele. Nicole is heterozygous brown eyed and has a flat nose. She marries Romy who is heterozygous brown eyed and a heterozygous pointy nosed person. What are the possible genotypes and phenotypes for their children? 2) In newts, skin color (blue verses green) and ruffle patterns (fringed verses spiked) are genetically inherited. A blue, fringed female whose father was green, spiked is mated to a blue, fringed male. a) In looking at all of the offspring from their matings, one finds that roughly 56% are blue, fringed; roughly 6% are green spiked; roughly 18% are blue, spiked; roughly 18% are green, fringed. What were the genotypes of the parents? b) If a blue, spiked was mated with green, fringed from this generation, what are the possible phenotypes (and the ratio) and the possible genotypes of the offspring? (assume both are heterozygous for the dominant trait) 3) What kind of gametes can be produced by the organisms with the following genotypes? a) AAbb b) AABB c) Aabb d) AaBb 8

9 Multiple Alleles & CoDominance In CoDominance, the Heterozygous Individual shows what Phenotype? 9

10 Genetic Linkage and Crossing Over 10

11 Linked Genes 1. Homologous chromosomes may bear either the same alleles or different ones at a particular location, making the organism either or for each gene. 2. When genes are located on separate chromosomes, they sort of each other during meiosis. 3. But what happens when genes are located on the same chromosome? The alleles for these genes would not be sorted into gametes independently since they would stay together during meiosis. The only way such alleles can sort independently is if they during Prophase I of Meiosis. 4. When alleles are located on the same chromosome and inherited together, they are called genes Sex-Linked Genes Any gene that is located on a sex chromosome is called a In humans, most sex-linked genes are found on the, which is considerably larger than the chromosome. Explain why none of the flies with white eyes was female in F1 generation. 11

12 More Practice Problems: 1. A woman has a baby and wants to prove who the father is. Her blood type is B and the baby is A. There are 2 possible fathers: Jim, who is type A and Mike who is type O. Which man could be the father? a. Either b. Jim c. Mike d. Neither e. Impossible to tell 2. In certain breeds of dogs, black color is dominant and red color is recessive; solid color is dominant and white spotting is recessive. A homozygous black-and-white spotted male is crossed with a red-and-white spotted female. What is the probability of their producing a solid black puppy? 3. A female fruit fly whose body is covered with forked bristles is mated with a male fly with normal bristles. Their offspring are 121 females with Normal bristles and 138 males with forked bristles. (ie: NO females with forked and NO males with bristles) Explain the inheritance pattern for this trait. What were the genotypes of the parents? What must be the genotypes of the male and female offspring? 4. Hemophilia (recessive sex-linked disorder) Normal male = Normal female = Hemophiliac Male = Carrier female = Hemophiliac Female = 12

13 Summary 1. Punnett Squares are Meiosis (gametes) along the sides and Fertilization (zygotes) on the inside squares. 2. In a Hybrid, the allele that shows up as the Phenotype is the Dominant allele, the other one is Recessive. This is the only way to tell which allele is dominant. 3. Segregation of alleles happens during Meiosis, when homologous pairs split and haploid cells (gametes) are formed because we never give our offspring BOTH copies of our alleles, only one or the other. 4. Independent Assortment is when you re looking at two traits at a time, one trait on one homologous chromosome pair, and another trait on a different pair. When they line up in Metaphase I, maternal and paternal chromosomes of the pair randomly line up over other maternal and paternal chromosomes independent of one another. In a dihybrid, that gives you 4 gamete outcomes. 5. Linked Genes are when the genes for two different trait happen to be on the same chromosome, so they do not independently assort. Example, sex-linked traits 13