Week 23

Monday, February 17, 2020: No School (Mid-Winter Break)

Tuesday, February 18, 2020 (HS-LS3-1): So far this unit, we have reviewed Central Dogma, reviewing how DNA codes for RNA which codes for proteins which ultimately determine our traits.  We learned about the structure of genes, including the regulatory region that turns genes on and off, as well as coding regions (exons) and non-coding regions (introns) which are excised during the processing of precursor RNA to messenger RNA (mRNA).  We learned that unlike mitosis (the process in which a parent cell divides to make two identical diploid copies of itself), during meiosis a parent cell divides to ultimately produce four haploid gamete cells (eggs and sperm), each with a random assortment of chromosomes that vary somewhat from each parent chromosome because of the process of crossing over.  We watched a video depicting the process of fertilization, picking up the story following the introduction of male sperm into the female reproductive tract, and learning for out of 300 million sperm, only one sperm ends up fertilizing an egg, thus kicking off the process of countless rounds of mitosis to produce a new individual.  Finally, we constructed one- and two-trait Punnett Squares to predict and analyze the inheritance patterns of traits passed along from two parents to their offspring.

To move our learning forward, we will focus on the chromosomes.  Humans have 23 pairs of chromosomes, 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes (XX = female and XY = male).  During the process of mitosis and meiosis, the chromosomes are copied and moved to the newly divided cells.  In mitosis, the 23 pairs of chromosomes (46 total) are copied exactly, resulting in two new cells, each with the same set of 23 pairs of chromosomes.  In meiosis, the successful result of meiosis II is the production of four cells, each with individual copies of chromosomes 1-22 and one of the sex chromosomes (23 total chromosomes).  However, sometimes the chromosomes don’t separate out perfectly.  In many cases, if one of the four daughter cells of meiosis II has an extra copy of a chromosome because they fail to separate (non-disjunction), and another cell is missing a copy of a chromosome because it went to that other cell with two copies, both cells will be non-viable.  However, there are well-documented cases where having an extra copy of a chromosome results in a viable human.  One example is called Trisomy 21, or Down Syndrome.

For our work today, we discussed the first three slides of the Down Syndrome Case Study slide deck and then detoured to the Wikipedia entry on aneuploidy.  We focused on the Types section of the entry, examining how, of the autosomal chromosomes, only Trisomy 21 will result in a viable fetus most of the time.  Students learned that when trisomy occurs in most of the other autosomal chromosomes, the result is an embryo that is non-viable, often resulting in miscarriage.

Back to the Case Study!  To learn how Trisomy 21 occurs, students watched a short video illustrating non-disjunction.  To put a human face on Trisomy 21, or Down Syndrome, students watched another short video about two young twins with Down Syndrome.  Both videos are shown below:

The second video naturally leads to questions about twins, so slide 5 explains the difference between identical and fraternal (non-identical) twins.  After slide 5, students will have time to read a Newsela article about possible a possible new treatment for Down Syndrome. After reading the article, students will respond to the writing prompt in the “Write” section of Newsela.

Wednesday, February 19, 2020 (HS-LS3-1): Welcome to the Chromosome Project!  You have the exciting opportunity to study a chromosome and learn about the genes that exist on a chromosome.  The goal of this project is to help you make a clear connection between DNA, genes, chromosomes, traits, and inheritance.

Your goals for today are:

  1. Check your student gmail to determine which chromosome you are assigned to research.  Autosomal chromosomes = 1-22 and the sex chromosomes are X and Y.  One you know your chromosome, a link to a list of all of the Chromosome Project Google Slide decks is located hereFor security, only students working on a specific chromosome may view and edit the slides for that chromosome.
  2. Research and write down what happens during human development if more than two copies of the chromosome are present.  What happens if only one copy of the chromosome is present?  Be sure to document your sources!  One resource is the Wikipedia entry on aneuploidy.
  3. Conduct a search for “genes on chromosome____” and insert your selected chromosome.
  4. Research at least 5 genes on your chromosome.  Research = write it down!  You must document your work to receive credit.  For each gene, write down the key information about each gene.  How?  Read below:

To research your gene, visit the NCBI Human Genome Resources page and enter your gene name into the “Search For Human Genes” box.  When the search completes, click on your gene name (typically the first gene on the list) and browse through the entry.  There is a ton of information provided!  For each gene, write down the following:

  • Official Symbol
  • Official Name
  • Your own one-sentence summary about the protein the gene codes for
  • Location of the gene on the chromosome
  • Number of exons in the gene
  • Length of the gene – hover your mouse over the top green line under the “genomic regions, transcripts, and products” and looking for the number after the aligned length (nt = DNA nucleotide bases) 
  • Length of the protein – hover your mouse over the top green line under the “genomic regions, transcripts, and products” and looking for the number after the protein length (aa = amino acids) 

Thursday, February 20, 2020 (HS-LS3-1): Select one of the genes from your list.  Research one trait associated with that gene and explain the connection between the gene and the trait.  For your final work, create a Google Slide with the following information:

  • Chromosome number
  • Brief description of what happens with too many or too few copies of the chromosome
  • For the gene you researched the most (and have trait information for):
    • Official Symbol
    • Official Name
    • Your own one-sentence summary of about the protein the gene codes for
    • Location of the gene on the chromosome
    • Number of exons in the gene
    • Length of the gene (in DNA bases)
    • Length of the protein (in amino acids)
    • Description of trait and how that is connected with your gene

Friday, February 21, 2020 (HS-LS3-1): Work day – continue your research and the Google Slide for your chromosome.