The genetics puzzle

This exercise is a part of Educator Guide: Snake Gulps and Chromosome Sequencing / View Guide
Illustration of a hand wearing a blue medical glove placing the final piece in a square puzzle that shows the letter Y.
Piecing together the human Y chromosome was tricky because of lots of repetitive DNA, but researchers have finally finished the whole puzzle.N. Hanacek/NIST

Directions for teachers

Ask students to complete the first set of questions with a partner. They will need to have a basic understanding of DNA and genes. Point them to the Science News Explores article “Explainer: What are genes?” for help with genetics and genomics vocabulary and definitions. Partners will need a sheet of paper or small poster board and markers or pencils for their diagrams.

Have students read the Science News article “The Y chromosome’s genetic puzzle is finally complete” individually, with a partner, or as a class. Make sure that a large space is clear on your wall or board. Put students in groups and provide sticky notes to each group. Ask groups to identify all the new pieces of information about the Y chromosome that were discovered in the two studies referenced in the article and have them write each piece of information on its own sticky note. Ask students to put their sticky notes in the designated space, overlapping any notes that have the same information.

As a class, review the sticky notes and add any findings that are missing. For each new finding, discuss what was known prior to that finding. Did it disprove information that was previously accepted as true? Then discuss how scientists reached the new finding, as described in the article.

Use the prompts in the third section below (“Putting the puzzle together”)to lead a class discussion about the future of genetics research based on the article.

Directions for students

Complete the first set of questions with a partner. Use the Science News Explores article “Explainer: What are genes?” and other “Scientists Say” articles for reference information and definitions of some of the terms.

Then read the Science News article “The Y chromosome’s genetic puzzle is finally complete” in class as directed by your teacher and complete the remaining prompts with your group and as a class.

Genetics basics

1. What is DNA and how is it organized? Where did you get your DNA?

DNA is short for deoxyribonucleic acid. It’s a molecule with a double helix structure that carries genetic information from one generation to another. Packaged into chromosomes within cell nuclei, DNA gives cells instructions for building and maintaining life, including the making of proteins. We get our DNA from our biological parents.

2. What are genes? What are alleles? How do they relate to a genotype?

Genes are the segments of DNA that provide instructions for making proteins. We get a version of a gene, called an allele, from each of our biological parents. A genotype is an organism’s complete set of genes.

3. Draw a Punnett square that shows the possible combinations of chromosomes between male (XY) and female (XX) sexes. Circle the instances in which chromosomes combine to produce a female-sexed baby and give the probability that this might occur.

Students should draw a Punnett square with four possible combinations of genotypes: XX, XX, XY and XY, and should circle instances of XX. The probability of these instances is 50%.  

4. With a partner, use the Science News Explores article “Explainer: What are genes?” to create a diagram that shows the relationships among the following terms: DNA, nucleotide, gene, chromosome, telomere, centromere, nucleus and cell. Think about starting with a sketch of a cell, labeling its parts, then creating more sketches as needed until all the terms have been depicted and labeled. Note: Some of the terms are linked to Science News ExploresScientists Say” articles that will give you more information.

Student answers will vary.

Gathering new puzzle pieces

After reading the Science News article, work in groups to identify every new piece of information that scientists learned from the new studies mapping Y chromosomes. Write each new finding on its own sticky note and place it on the wall of your classroom. Check to see if other groups already put sticky notes with similar information on the wall — if so, overlap your sticky notes.

As a class, review the sticky notes and add any findings that are missing. For each sticky note discuss what was known prior to the new finding. Did that finding disprove information that was previously accepted as true? Then, discuss how scientists determined the new finding and what challenges they faced, as described in the article.

Two example answers are given below.

New finding: Scientists mapped the entire Y chromosome.

What was known prior: Prior to these two studies, scientists had never mapped the entire Y chromosome, and only understood it in parts.

How scientists determined the new finding: Scientists worked to put the puzzle of the Y chromosome together, navigating challenges like palindromic sequences of DNA and repeated sequences of DNA.

New finding: The TSPY2 gene varies in location from person to person.

What was known prior: Before the study mapping 43 Y chromosomes — when there was only one reference Y chromosome that was not fully sequenced — it was thought that the TSPY2 gene was located near the tip of the Y chromosome.

How scientists determined the new finding: By comparing the Y chromosomes from 43 men, the scientists discovered that the TSPY2 gene could be located at one of two places.

Putting the puzzle together

1. Why was the sequencing of 43 people, 21 of whom were of African descent, integral to the ability of scientists to discover the findings in this study?

The number of Y chromosomes sequenced increased the data sample size from the earlier reference chromosome. The new sample also came from a diverse group of people. This allowed the scientists to make comparisons among the chromosomes to discover differences.

2. Based on the article, what is one takeaway about what is important in the design of genetics research studies?

Student answers will vary but should reference the need for multiple data points that are gathered from a diverse range of subjects.

3. What do you think the next step should be for the scientists in the article? Why?

Scientists should continue their sequencing of Y chromosomes, making sure the chromosomes are from a diverse group. Gathering more data will allow them to gain a better understanding of potential medical applications and implications.