Download Mendel`s Laws There are two main Laws of Inheritance developed

1 Mendel’s Laws There are two main Laws of Inheritance developed by Mendel. •
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Law of Segregation Law of Independent Assortment What exactly are these laws? Let us start with the Law of Segregation. Place 5 green beans in a container. This will be your container “1” representing the father’s Sperm Cells. In another small box or container, place 5 beads or small paper ball in the container. The second container will be the mother’s haploid egg cells. Draw all the items in each container: Container 1 – Father’s Sperm Cell Container 2 – Mother’s Egg Cell In Mendel’s experiment, he bred Green Peas with Yellow Peas and observed the number of offspring. In this activity, we are going to use Green Beans to represent 1 allele of a gene. In this case, Green Beans will be a Dominant Gene (B) accounting for the Phenotype of Green color, while the other Beads will represent the Recessive Allele (b) accounting for Yellow color Phenotype. Summarize in words in the table below: Phenotype Genotype Green Beans Dominant or Recessive Other Beads Start your F1 Generation (1st generation) by Randomly picking one from the Father’s container, and one from Mother’s container. Record the genotype of each trial in the table below. Trials 1 2 3 4 5 Father 1. What was the phenotype of your F1 generation? Mother Genotype Phenotype 2 Prove this by using Punnett Squares: Father’s Genes Mother’s Genes Now, what was remarkable about Mendel’s experiment was that he bred the F1 generation to produce F2 generation and observed the results. To re-­‐create the genes found in the offspring of the 1st Generation, place the same number of Green Beans and Beads in the containers. In this activity, we can use 5 Green beans and 5 Beads in EACH of the two containers. Draw all the items in the Containers (Testicle / Ovaries) Container 1 – Father’s Sperm Cell Container 2 – Mother’s Egg Cell Repeat the Fertilization process by Selecting one from Container 1 and one from Container 2. Trials 1 2 3 4 5 6 7 8 9 10 Father Mother Genotype Phenotype 2. What was the phenotype of your F2 generation? Establish in a percentage. 3. What should have been the ‘theoretical percentage’ of the phenotype? ________________________ 3 Use Punnett Squares to prove this. Father’s Genes Mother’s Genes So what exactly is Law of Segregation? What Mendel noticed was that in the F1 generation (1st generation), all the offspring had one particular trait from one of the two parents (green peas). Similar to our activity, our F1 generation had 100% green peas. When he self-­‐
pollinated the F1 generation (selecting two 1st generation as parents), he noticed the phenotype from the parents had skipped a generation. Therefore, he believed the allele pair (both copies of the traits) separates when gametes are produced. In other words, he believed that the two sets of genes (allele pair) actually segregates when sperm or eggs cells are produced. This was later proven to be true when the stages of meiosis were discovered and that meiosis undergoes two rounds where Meiosis II divides the diploid into haploid cells. Formal definition of Law of Segregation: The principle stating that during the production of gametes the two copies of each hereditary factor segregate so that offspring acquire one factor from each parent. Questions: 1. How come there are two copies of “Bead type” in each of the two containers (Sperm and egg cell containers) in the F1 generation? 2. From which part of the activity is the Law of Segregation demonstrated? 3. Using your own words, what does Law of Segregation mean? 4. Provide your own original example of Law of Segregation. 4 Law of Independent Assortment Let us investigate on the Law of Independent Assortment. Investigating the Law of Independent Assortment requires us to look into Punnett Squares into dihybrid crosses. So far, you have completed Punnett Squares involving Monohybrid crosses. Monohybrid crosses are when 1 allele pair (1 trait pair) is crossed with each other. But in dihybrid crosses, two separate traits are crossed. In this activity we will use 2 traits: The new traits will be M & Ms dominant for Chocolate and Skittles recessive for Candy Phenotype Genotype Green Beans Dominant or Recessive Other Beads M & Ms Skittles Create the following: 2 Containers with the 5 Green Beans, 5 Beads, 5 M & Ms and 5 Skittles in each Label the following two containers Container 1 – Father’s Sperm Cell Container 2 – Mother’s Egg Cell Again, these containers will represent the Father’s Sperm cells, and Mother’s Egg cells. Create your F1 generation by randomly selecting 1 from the Father, and 1 from the Mother. Fill in the table below Trials 1 2 3 4 5 6 7 8 9 Father Mother Genotype Phenotype 5 1. What was the problem with selecting from the two containers? Now revisit your experimental design and create the following. Use 4 containers (4 sets) and fill the container with following: Container 1: 5 Beans (B) & 5 Beads (b) Container 2: 5 M&Ms (M) and 5 Skittles (n) Container 3: 5 Beans & 5 Beads Container 4: 5 M&Ms and 5 Skittles Container 1 – Father’s Sperm Cell for allele 1 Container 2 – Father’s Sperm Cell for allele 2 Container 3 – Mother’s Egg Cell for allele 1 Container 4 – Mother’s Egg Cell for allele 2 Now, complete the 10 trials by selecting 1 from container 1 & 2 and 1 from container 3 & 4 Mother (Allele 1) Father (Allele Mother 2) (Allele 2) Genotype Phenotype 1 Father (Allele 1) 2 3 4 5 6 7 8 9 10 Trials 2. What was the percentage of finding a Green and Chocolate phenotype? Express in percentage 3. What was the percentage of finding a Yellow and Candy phenotype? Express in percentage 6 In Mendel’s experiment, he noticed that the percentage of getting Double Dominant (Green and Chocolate) was 56% and a Double Recessive (Yellow and Candy) was 6%. Were your results similar to Mendel’s results? Try completing a dihybrid cross Punnett Square: In your example, you crossed a heterozygous Brown and chocolate with a heterozygous Brown and chocolate. The genotype should be: BbMn x BbMn For each, select 1 gene from each allele pair; B or b from Bb and combine with the 1 gene from the other allele pair; M or n from Mn. In this case, we will have BM, Bn, bM, and bn. Fill in the Punnett Square and complete. Father’s Sperm cell Mother’s Egg cell 4. What is the phenotype for Brown and Candy? Express in percentage 5. What is the phenotype for Yellow and Candy? Express in percentage 6. What is the phenotype for Brown and Red? Express in percentage 7. What is the phenotype for Yellow and Red? Express in percentage So what exactly is Law of Independent Assortment? Law of Independent Assortment is saying that the different alleles (Color and Candy type) are treated independently from each other. In our first attempt of the activity, it had errors because there would be an overlap of the same allele, but in our second attempt when the alleles were separated in their own containers, we see that there is a Independent assortment of the Genes. This is due to the crossing over that occurs in Meiosis. Formal definition of Law of Segregation: When each member of a pair of homologous chromosomes separates independently of the members of other pairs so the results are random Try the other practice dihybrid cross worksheets. Keep this to have an understanding of Mendel’s 2 laws.