Biology
Chapter 8: 11-23 Cell Reproduction - Meiosis and Chromosome Defects
Homework
Biology Homework Chapter 8: Cell division - Meiosis
Homework
- Reading Preparation
- WebLecture
- Study Activity
- Preparation work for chat
- Online Quiz
- Lab Instructions
Reading Preparation
Textbook assignment: Chapter 8:The Cellular Basis of Reproduction and Inheritance, sections 11-23.
Study Notes
- 8.11 This section introduces the manufacture of special cells (diploid or gamete cells) that can form new organisms. These cells have only half the genetic material normally found in somatic cells in the same organism. In eukaryotic cell reproduction, this involves matching pairs of similar genetic material (homologous pairs) from two different cells, followed by multiple divisions. Obviously, the resulting cells are not clones of the parent cells, but something new.
- 8.12 The production of gametes occurs through meiosis; each gamete has only one copy of the species' chromosomes. The production of a new organism occurs when gametes fuse.
- 8.13 The process of meiosis follows similar stages to mitosis, but repeats twice to provide four gametes with half the chromosome content of the original cell.
- 8.14 Compare meiosis to mitosis at each phase. Note the differences:
- formation of chromatids (mitosis prophase) vs the formation of tetrads (meiosis prophase I)
- remix of chromatid strands through crossing-over during meiosis metaphase I
- separation of chromatids (mitosis anaphase) vs the separation of tetrads into chromatids (meiosis anaphase I)
- a second cycle of phases in meiosis to form haploid gametes
- 8.15 Random recombinations during meiosis metaphase I increase genetic diversity. The same parents will have children with unique characteristic combinations (except in the rare case of identical twins)
- 8.16 The same chromosome with the same gene pattern may have different forms of each gene on each of the two chromosomes present in a parent. Haploid gamete production ensures that a gamete possesses only one of these copies from each parent.
- 8.17 In addition to random selection of one chromosome strand from a pair, crossing-over mixes gene combinations up, so that the inherited chromosome strand in the gamete is different from the original copy in the parent.
- 8.18 Extra chromosomes cause certain problems, because the nucleus receives duplicate instructions and does some things more often than it would otherwise. In particular, extra copies of chromosome 21 (trisomy-21) causes Down syndrome, a genetic defect that can result in abnormal physical and mental development.
- 8.19 Karyotypes are used to identify and sort human chromosomes for study.
- 8.20 Chromosome defects occur when chromosomes fail to separate properly during meiosis I or meiosis II. Gametes that entirely lack a chromosome will not usually produce viable offspring. Gametes with extra copies of chromosomes may produce viable but abnormal offspring.
- 8.21 When disjunction leads to abnormal sex chromosomes, the result may not be fatal, but will cause some problems.
- 8.22 In some situations, chromosome defects make it impossible for offspring to mate with other members of their parents' species; in this case, they become a new species. New traits may give them a survival advantage.
- 8.23 If chromosome replication fails, so that genes are changed or missing, the key information controlling cell development and regulation is scrambled. Cells may develop irregularly or out of control (cancer).
Web Lecture
Read the following weblecture before chat: Chromosomal Defects
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Use the John Kyrk meiosis animation to step through the two cycles of mitosis-like phases in meiosis, the process used to form gametes. Note how the phases differ from mitosis proper, and how the two cycles differ from each other. Pay attention to the way DNA is mixed between chromosomes during crossing-overe in prophase I.
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.
Chapter Quiz
- 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.
Lab Work
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.
- Lab Instructions: Complete the lab on Cell Division Lab/AP Investigation #7.
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