Module 6

1. Module 6

1.4. Page 2

Lesson 1

Module 6—Mendelian Genetics: The Transmission of Traits to the Next Generation

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Early Theories

For thousands of years, farmers have used seeds from good crops to improve the characteristics of the next year’s crop. They breed the best individuals in their livestock to improve the next generation’s chances of expressing favourable traits. How favourable traits are passed on has been the interest of scientists for centuries. Early theories tended to accord importance to the kind of life the parents led. Similar to Lamarkian’s ideas of evolution, where body parts change in response to use, many early scientists believed life’s experiences influenced the next generation’s traits. These theories were finally put to rest by a nineteenth-century, Austrian monk named Gregor Mendel. Mendel studied garden peas as his experimental subjects and, with breeding and observation, laid the foundation of our current knowledge and understanding of heredity and genetics.

Read the sections “Early Theories of Inheritance” and “Developing a Theory of Inheritance: Gregor Mendel’s Experiments” on pages 586 to 588 in your textbook. Answer the following questions to ensure your understanding. Save the answers in your course folder. Remember to create a flash card or text entry for each new term you encounter.

TR 1. Where did Aristotle believe the factors for inheritance were located in the body? How did he believe these were passed down?

TR 2. What were some of the likely problems early scientists must have encountered when trying to explain inheritance?

TR 3. Examine the seven traits Mendel studied on page 588. What do you notice about all of them?

TR 4. What is a monohybrid cross?

TR 5. Explain how a hybrid plant is different from a true breeding plant.

TR 6. Explain the difference between P, F1, and F2 generations in a cross.

monohybrid: an organism that is heterozygous for one trait (e.g., Tt)

hybrid: the offspring of two parents with different inheritable traits; often termed heterozygous

true breeding: organisms that produce offspring that express the same trait generation after generation; organisms are homozygous for a trait

P1 generation: the first set of parents; parents of the F1 generation

F1 generation: offspring of the P1 generation; F stands for filial generation—meaning brothers and sisters

F2 generation: offspring produced as a result of individuals of the F1 generation mating with other individuals of the F1 generation

Watch and Listen

Watch the video “Classical Genetics and Monohybrid Crosses” until you reach the section “Bio Challenge: Round vs. Wrinkled Peas.” Answer the following questions for your own understanding. Consult with your teacher about the answers.

TR 7. Who discovered that cells differentiate during embryonic development and disproved the idea that the egg or the sperm held a complete miniature organism?

TR 8. Explain the meanings of the terms dominant and recessive factors (we now call these factors alleles).

TR 9. Distinguish between the terms gene, allele, and chromosome.

TR 10. What process creates gametes?

TR 11. How do we distinguish between dominant or recessive alleles when drawing them on a chromosome or in a Punnett square, which you will study in the next lesson?

TR 12. What does it mean to be homozygous for a trait? How is this different from being heterozygous for a trait?

TR 13. Using an example, distinguish between the terms genotype and phenotype.

dominant: if two alleles are present, the allele that is expressed is the dominant one (e.g., if an individual has both tall and short alleles, but is tall, then tall is dominant over short)

recessive: if two alleles are present, the allele that is hidden is recessive

homozygous (true breeding): a genotype where both alleles are the same (e.g. ,TT is homozygous dominant, tt is homozygous recessive)

heterozygous: a genotype where the alleles are different (e.g.,Tt)

genotype: what the genes say; two symbols that indicate which alleles the individuals has for a particular trait (e.g., Tt)

phenotype: the observable characteristic of the organism (e.g., tall height or short height); is determined by genotype (e.g., the Tt genotype results in a tall phenotype)

This photo shows tall and short pea plants.

If you want more information about Mendel’s experiments, do an Internet search using search terms such as ”biology + Gregor Mendel + Experiments with Peas.” There are many animations and interactive experiments available on the web.

Try This

From your reading and the video, apply your understanding to the following questions. Discuss your work with your teacher and save the results in your course folder.

TR 14. Why did Mendel choose to study pea plants in his experiments?

TR 15. How did he ensure that his plants were true breeding?

filial: the offspring of a cross

TR 16. What does filial mean?

TR 17. How did Mendel make sure his results were statistically accurate?