Lesson 3.6.1

3.6.1 page 3

Read

As the video clip has already introduced, Mendel discovered two variations of traits for each characteristic that he studied. One trait is dominant over the other. The evidence for this was discovered when he crossed two pure plants with contrasting traits, such as Tall (T) or short (t) plants for example. The first generation plants, or F1, were all Tall. The short trait seemed to disappear. However, when these plants self fertilized, their offspring, the F2, were a mix of Tall and short plants. Read the section “Dominant and Recessive Genes” in your text on page 588 for a better understanding of this mode of inheritance.

 

Mendel proposed that each trait was controlled by factors. We now call these factors genes, and the different forms of genes are termed alleles. Each plant will have two alleles present for each characteristic, and will pass down only one of these alleles when they create gamete cells (Sperm or egg). The combination of the two alleles received by a gamete is random, and this type of separation is known as Mendel’s first law; The Law of Segregation. For a greater understanding of this law, please read “The Law of Segregation” in your text on page 589.

Self-Check

Complete the following set of questions to see how much of these genetics concepts you have begun to internalize!

 

  1. Separate the 2 chromosomes by meiosis

 

 

  1. What type of cell is formed as a result of meiosis?
  2. What term is used to describe “T” and “t”?
  3. Which of Mendel’s Laws does the above example illustrate?
  1. Place the appropriate term in the space provided for each picture. Use the following words: genotype, phenotype, segregation.

             Blue eyes                           bb                               
    a. _______________          b. ________________        c. __________________
  2. Indicate whether each of the following is a trait or a characteristic:

    1. wrinkled seed
    2. curly hair
    3. pod color
    4. plant height
  3. How many different types of gametes would an individual with the following genotypes produce (hint: each gamete will contain only one from each letter pair):

    1. AABBCC
    2. AaBbCc
    3. AaBbCC
  4. What are the gamete types produced by an individual with genotype WWTtPp?
  5. What evidence is there for Mendel’s principle of dominance?
  6. Which term identifies or describes these genotypes:

    a) Rr/Pp –                          b) RR/PP –
Check your work.
Self-Check Answers

 

  1. the cells created by meiosis are called gametes
  2. the “T” and “t” are known as alleles, with “T” being dominant and “t” being recessive
  3. The Law of Segregation
  1. a) phenotype, b) genotype, and c) segregation
  2. Trait or Characteristic
    1. wrinkled seed            trait
    2. curly hair                  trait
    3. pod color                  characteristic
    4. plant height              characteristic
  2. Gametes

    1. One
    2. Eight
    3. Four
  1. WTP, WTp, WtP, Wtp – four unique gametes
  2. The reappearance of the recessive trait in the F2
  3. a) heterozygous         b) homozygous or true breeding.