Biology Homework Chapter 9: Complex Inheritance
Textbook assignment: Chapter 9: Patterns of Inheritance, sections 11-23.
- 9.11 Incomplete dominance occurs when neither allele is completely dominant, so both are expressed to some extent in a heterozygous individual, where the resulting phenotype is partway between the phenotype of the homozygous dominant and homozygous recessive genotypes.
- 9.12 Blood types demonstrate the situation where a phenotype is controlled by multiple alleles at the same time. In the case of AB individuals (genotype IAIB), the alleles are codominant: both are fully expressed.
- 9.13 Besides incomplete dominance and codominance, where a trait is controlled by the alleles of one gene, there are some situations where a single gene can affect multiple traits (pleiotropy). An interesting example of this effect is sicklecell anemia, a disease which actually gives its victims an advantage in surviving the more deadly disease, malaria.
- 9.14 The opposite case is also possible: a single characteristic, such as height or skin color, can be influenced by many genes. (And you thought this was going to be simple: one gene, one trait....sorry).
- 9.15 Genetics alone doesn't influence growth and development, or skills acquisition. Environmental factors, especially nutritian, or exposure to sunlight, can affect the extent to which some genes are expressed in an individual.
- 9.16 Mendel didn't have a way to explain why traits were inherited according to statistical laws, but we can explain inheritance patterns as the transfer of genes on chromosomes. Work through diagram 9-16 following one of the traits on one the chromosomes, then do it again with a different trait.
- 9.17 The law of independent inheritance doesn't work for all traits. Genes on the same chromosome tend to be inherited together unless split by the process of crossing over. The closer the genes are on a single strand, though, the less likely they are to be split apart and act as though they were inherited independently.
- 9.18 We need to look more closely at crossing over, and the way it affects the inheritance of genes on the same chromosome. The recombination frequence of two such genes that start out on the same chromosome can tell us something about how far apart the genes are. Pairs of traits that show up in "recombinations" more frequenlty are further apart than pairs that show up less frequently. Crossing over is more likely to split apart genes that are far apart on the same chromosome (because there are more places between them to break the genes apart), than genes that are close together.
- 9.19 Using inheritance patterns of the same pair of genes, we can determine the relative locations of the genes.
- 9.20 The human X and Y forms of the 23 chromosome carry sex-determining traits. Many species have special chromosomes that carry these traits, while the other chromosomes for the species are otherwise identical across the sexes.
- 9.21 Because females inherit two X chromsomes (XX pair) and males inherit an X and Y (XY pair), the inheritance patterns of genes on these chromosomes follows a different pattern from those on the other 22 "autosomal" chromosomes.
- 9.22 Males more likely to be affected than females to be affected by sex-linked diseases or conditions. In females, the XX chromosome is redundant: if one is defective, the other may still function. In males, XY is not redundant, so if eithr the X or the Y is defective, it has no backup copy that is correct to compensate.
- 9.23 Unusual traits, especially on the Y chromosomes passed only by males, can help us map inheritance through historical periods.
Read the following weblecture before chat: Traits and Genes
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. (If you have not already done so, follow the instructions in the previous assignment to become familiar with the simulation).
Chose "Select a Practice Population" and use the right arrow to move to the third practice population,, which involves sex-linked traits. Click on "Continue".
- Study the parent generation and decide which crosses you will perform to determine which traits are sex-linked.
- If you are feeling like being seriously challenged, use population 7 and see if you can determine the linking and positions of traits on the same chrmosome.
- Required: Complete the Mastery Exercise with a score of 85% or better.
- Optional: Test yourself with the textbook multiple choice questions and note any that you miss that still don't make sense. Bring questions to chat!
- Go to the Moodle and take the quiz for this 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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