Meiosis, part 1

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Objective

Students will be able to explain how genetic variation results from the changes that occur to chromosomes during meiosis.

Big Idea

Making sex cells is double the fun of mitosis.

Warm-Up

5 minutes

Warm-Up: Explain the difference between diploid and haploid chromosome numbers.

This question serves as a review of the previous lesson, Cell Division-Mitosis.  Look for students to be able to identify that the diploid chromosome number represents the full number of chromosomes for an organism, while the haploid chromosome number reflects half the full number of chromosomes for an organism.  Some may recall that the somatic cells are diploid and sex cells are haploid.

Inform students that today’s lesson will allow students to learn how sex cells are produced and how the formation of sex cells promotes genetic variation within species.             

Introduce New Material

20 minutes

Begin the lesson with a video clip, Meiosis - The Continuation of Life. 

After the clip ends, go right into the lesson by introducing the vocabulary associated with the lesson:  somatic cell, gamete, zygote, haploid, diploid, chromosome, crossing over, meiosis, genetic variation, homologous, sister, non-sister, spermatogenesis, oogenesis

Say each word aloud and ask students to repeat the term after you.  Clap out the syllables for the terms with 3 or more syllables.  This helps students hear the word parts of more complex terms so that they can pronounce them correctly. 

Instruct students to add the bolded terms to their vocabulary maps. Remind students that the bolded terms contain prefixes, suffixes, Greek or Latin root words.  Provide explicit instruction of each term when it arises during the course of instruction.

Inform students of the learning target for this lesson:

  • I can explain the process of crossing over and how it creates genetic variation.
  • I can explain the differences between mitosis and meiosis.

Distribute guided notes and spend about 15 minutes sharing specific content points about meiosis.  Display visual information as you instruct and ensure students take notes using the guided notes that you have provided or use a note-taking strategy that you have taught.  Guided notes provide greater support for the different learning styles of students. 

It’s a good idea to provide highlighters for students to use as they take notes and guide them in what points they should highlight in the notes. 

Walk around as you teach the pertinent information to ensure that students are writing accurate information on the guided notes that you have provided.  Openly acknowledge to the class, those behaviors by students that demonstrate taught skills such as use of highlighters and adding to the notes by writing additional information in the margins.  

Use of visual aids help students understand the difference between homologous chromosomes and sister chromatids.  Images and animations are always a good resource.

Stop at various points during the instruction and model skills that students are expected to know or do. For example, after discussing homologous chromosomes, engage students in an activity,  identifying homologous chromosomes.  Display the visual image and ask a student to read the instructions aloud to the class.  Model critical thinking by performing a “think aloud” for question 1. Give students a few minutes to derive answers to the remaining questions before going each question with the class, being sure to explain how each correct answer was derived.

Guided Practice

10 minutes

Display and distribute copies of the meiosis vocabulary assignment.  Note: Distribute copies of the same ppt slide.

Instruct students to use each of the ten vocabulary words in sentences or drawings that show their understanding of what the term has to do with cell division.  Inform students that at least 5 of the terms should be represented with drawings.

Select one of the terms to model how students should complete the assignment, using a “think aloud”.   This practice allows students to observe the thinking that must occur to complete the task.  Remind students that the emphasis is not on artistic ability but on one’s ability to convey in words or simple images a clear understanding of the terms association with meiosis.

Independent Practice

20 minutes

Distribute markers and paper.  Instruct students to work independently to complete this formative assessment.  Walk around to observe how well students are able to complete the assignment. Encourage students to use their notes as a reference.  For this type of activity, consider using this policy, “Ask three before me”.  This will encourage students to be more resourceful and persistent on their own before seeking my guidance.

The student work samples clearly demonstrate that students were able to creatively depict their understanding of the associations between the terms and meiosis, as well as use the terms correctly in sentences.  Student work 1 shows that the student possess a clear understanding of the terms and with minimal art skills is still able to to convey understanding of the terms. Student work 2 conveys a greater depth of understanding because the visual work includes details  as shown by the alleles written on the sister chromatids.  Student work 3 and student work 4 are of a similar quality and detail, with more detailed sentences shown in student work 3.  All four student work products display mastery, each with differences that show individual student's depth of understanding.

Close

5 minutes

Display the following Mitosis and Meiosis table, leaving it blank for student to complete as a whole group:

 

MITOSIS

MEIOSIS

RESULTS IN

2 diploid cells (2n)

4 haploid cells (n)

CELLS ARE

Genetically identical

Genetically different

OCCURS IN

Somatic (body) cells

Gametes (sex) cells

Observe how readily students are able to respond correctly to each of the prompts.  Use your observations as information that will drive the next day’s instruction.