Biology Homework Chapter 9: Mendelian Inheritance
Textbook assignment: Chapter 9: Patterns of Inheritance, sections 1-10
- 9.1 The ancient theory of pangenesis used to explain inherited characteristics, including "learned" characteristics, gave way in the nineteen century to a theory of blended characteristics. Neither theory could explain what we now call recessive traits, that while not expressed in one generation, can still be passed to subsequent generations.
- 9.2 The Austrian biologist and monk, Gregor Mendel, based his theory of inherited characteristics on strict mathematics using statistical methods to analyze the results of cross-fertilization and self-fertilization to produce thousands of examples of inheritance in pea plants.
- 9.3 The concept of the allele is crucial. In the simplest scenario, a given gene controls a single trait, say eye color. It can have various forms, resulting in different versions of the trait, say blue or brown. The different forms of the gene are the alleles of that gene. Since a normal cell has two copies of each chromosome and thus two copies of the gene, if the copies have different alleles, one will be dominant (expressed), or recessive (not expressed), or partially expressed. Get the terms here straight: heterozygous vs. homozygous tells you the alleles in the pair are different or the same. What are the implications of Mendel's "principle of segregation"?
- 9.4 Here, you need to understand that the alleles for a particular gene reside at the same place on each strand of the chromosome (assuming no defects). Even after crossing over, the gene locations are the same, only the alleles have changed.
- 9.5 The law of independent assortment means genes are inherited individually, without connection to other genes. This isn't always true, as we shall see, but it does hold for genes on different chromosomes. Study the Punnett square! Be sure that you know how to construct the square for 2 genes with 2 alleles (shown) and 4 genes with 4 alleles. What is the difference between a phenotype and a genotype? Can you use a genotype to predict the phenotype of a simple trait? Can you use a phenotype to predict the genotype of a simple trait?
- 9.6 What is a testcross? How could you use it to determining the genotype of a parent from phenotypes of the offspring? When are the results of a test cross conclusive, and when are they only able to indicate the likelihood of a genotype for a parent?
- 9.7 If you have had any math that dealt with permutations and combinations, here is a practical application for that math. Just remember that the probability for any two things happening simultaneously is the product of the probability that either one will occur: you have to multiply.
- 9.8 The pedigree chart shown here is a standard format: males are squares, females circles, and the phenotype (expressed trait) is show as dominant trait light, recessive trait dark. If present, a dominant allele is always expressed in favor of a recessive; a recessive is expressed only if it is homozygous. So a dark marker means a recessive trait is expressed and the genotype (both alleles present) must be two recessives. However, you have to look at the descendents to determine whether the recessive allele is present. If you have a recessive expressed in a child, then each parent must have a recessive allele and be heterozygous. If a recessive and a dominant have a recessive child, then the dominant parent must have a recessive allele and be heterozygous.
- 9.9 Genetic disorders are defects in one gene (as compared to chromosomal disorders, where multiple genes or the whole chromosome is affected). Study the examples. In particular, be able to explain why a fatal dominant disorder such as Huntington's disease hasn't died out in the general population.
- 9.10 Be able to explain the information and dangers of each type of fetal testing, and consider the ethical issues of such testing.
Read the following weblecture before chat: Mendelian Inheritance
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Use the Classical Genetics simulator to explore traits in Drosophila populations. Clcik on "Learn more" to read the instructions. You do not need to log into an account to use this exercise; we will use the practice populations only. You will not be able to save your population, but the exercise should give you a sense for how inheritance can be determined.
Chose "Select a Practice Population" and when you see the first practice population, note the purpose (segregating body time for autosomal inheritance) into dominant wild type and recessive tetrapter types. Click on "Continue".
- In the lab, click on the Stats tab and note the number of body types present. Estimate the best whole-number expected ratios for your sample. For example, if you have a random population with a single simple trait, 75% should show the dominant trait and 25% should show the recessive trait. Enter these values and calculate the Chi-Square value for your data.
- Click on the organism tab and sort by body types and display body types. Are all specimens showing the recessive trait homozygous? Are all specimens showing the dominant body type homozygous?
- Predict the relative ratios of body types in new populations if you breed
- Recessive to recessive
- Recessive to true-breeding dominants
- Recessive to heterozygous dominants
- Sort by sex but display body types. Then perform the crosses for which you made predictions (these will inhabit new vials). Select each vial and view the stats on it; enter your prediction and compare the Chi-square value with the actual results.
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- No quiz yet: the Chapter Quiz opens when we finish the chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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