How do living things pass traits to their offspring?
Learning Targets
Learning Experiences
Learning Targets
Learning Experiences
Misconceptions V Chromosomes always appear as an “X” shape. In sexually reproducing organisms, half of the organism’s body cells contain DNA from the mother and half contain DNA from the father. V A gene and the expression of the gene as a characteristic or trait are the same thing. V The timing of the occurrence of an environmentally induced characteristic will affect whether the characteristic is transmitted to offspring. V In asexually reproducing organisms, half of the parent’s DNA is passed to its offspring. V Some characteristics of an offspring are determined by the parents’ environmentally acquired characteristics.
83 I can compare and contrast mitosis and meiosis in terms of chromosome number and number of daughter cells and in comparison to the precursor cell. (12) 84 I can develop a model of chromosome movement at multiple points during meiosis and use the model to determine when cells are haploid and diploid. (12) 85 I can identify when crossing over occurs and can explain the significance of crossing over in genetic variation. (12) 86 I can compare and contrast the genetic makeup of cells before meiosis, after meiosis, models, comparing them to the biological process, and identify strengths and weaknesses of the model. (12) 88 I can use meiosis models to explain the phenomena seen in a simple pedigree. (12) and after fertilization. (12) 87 I can evaluate meiosis
This series of activities illustrates the process and products of meiosis. Students begin by comparing diagrams of mitosis and meiosis and listing differences between the two. This list is expanded and refined as students dig deeper into meiosis through additional activities, through classroom instruction, and by viewing online resources related to meiosis. Working collaboratively, students use the chromosome representations described for learning target #83 to model the stages of meiosis, taking particular note of: • the timing and events associated with crossing-over and the role this process plays in generating genetic variation among offspring • points in the cycle when ploidy changes (diploid to haploid) • the difference between what is segregated during the first and second division (homologous chromosomes and sister chromatids, respectively) • the similarities and differences between the final products of meiosis (gametes) when compared with each other and to the progenitor cells To simulate fertilization, students select a single gamete and combine its genetic material with the gamete from another group. They compare the genetic information present in the resulting zygote to that of the parental cells. Students critique the chromosome model they have been working with, identifying how the model correctly mimics chromosome structure, describing the model’s limitations and suggesting ways the model could be improved. Pose a problem: Show a pedigree of a family where one child has a genetic disorder and another does not. Ask students to explain how this is possible, using what they’ve learned about meiosis and demonstrate using models. At this point in instructions, students are not expected to create or analyze pedigrees, but to relate the information in the simple pedigree to chromosome movement in meiosis. More detailed analysis of pedigrees and inheritance patterns occurs later.
82 I can develop a model of a replicated and non-replicated chromosome to compare their structure and use scientific vocabulary to describe chromosome structures. (4, 12) Teacher Tips Chromosomes appearing as an “X” shape are replicated chromosomes consisting of two sister chromatids. Meiosis models can be constructed using pipe cleaners, yarn, socks, pool noodles, or other craft materials. The type of materials used to construct models is less important than correctly showing chromosome movement and ploidy level at multiple points in the system. Inappropriate models may contribute rather than dispel student misconceptions. It is important to ensure that students can accurately relate the chosen manipulative to the actual biological process.
Students extend the previous discussion regarding DNA replication to the entire chromosome, discussing when during the cell cycle replication occurs and how it is initiated at multiple places along each chromosome. Students analyze models or annotate diagrams of chromosomes to identify the features relevant for upcoming conversation regarding meiosis (telomeres, centromeres, sister chromatids, homologous chromosome pairs, replicated and non-replicated chromosomes). They may return to the chromosome models used in learning targets #36-39 or build new models using chenille sticks, pool noodles, socks, etc.
Teacher Resources
ChromoSocks or other manipulatives (i.e., pipe cleaners, pool noodles, yarn) can be used as models to illustrate replication and chromosome structure. ChromoSocks — HudsonAlpha Institute for Biotechnology Kit uses socks as model chromosomes to mimic the movement of chromosomes during cell division. This kit, developed at HudsonAlpha, is available for purchase from Carolina Biology, from ASIM as C4Chromo and was distributed at GREAT: Cell Division workshops in 2015/16.
Misconceptions
V All pedigrees are for deter- mining sex-linked traits. V The process of meiosis is the same as mitosis but cell division occurs twice. V Gametes (sex cells) are the same as sex chromosomes. V All genetic disorders are caused by chromosomal anomalies and are visible on a karyotype.
Teacher Resources
ChromoSocks — HudsonAlpha Institute for Biotechnology Kit uses socks as model chromosomes to mimic the movement of chromosomes during cell division. This kit, developed at HudsonAlpha, is available for purchase from Carolina Biology, from ASIM as C4Chromo and was distributed at GREAT: Cell Division workshops in 2015/16. Meiosis and Fertilization – Understanding How Genes are Inherited Students will use chromosome models to simulate the processes of fertilization and meiosis. bit.ly/meiosis-and-fertilization What is Meiosis? — Concord Consortium Students participate in a virtual simulation to explore genetics and heredity by studying and breeding virtual dragons. Students will control the process of fertilization and meiosis. bit.ly/what-is-meiosis NOVA Flash Animation — NOVA This website animation allows students to view the similarities and differences between the processes of mitosis and meiosis. bit.ly/mitosis-and-meiosis
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Teacher Tip It is recommended that students
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be provided opportunities to apply what they’ve learned with one chromosome model to a novel model. When given a new model, can they identify representative structures, strengths and weaknesses? This evaluation often reveals persistent misconceptions.
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59
A Field Guide to the Alabama Standards
58
The Biology Compendium
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