Nettie Stevens: The Genetics Pioneer Who Discovered Sex Chromosomes

At a time when women mostly married and stayed home, or were teachers or nurses if they wanted to work, Nettie Stevens became a research scientist and her discoveries changed genetics forever.

NettieStevensGeneticsPioneerOnce she graduated with her PhD in 1903, she and a colleague (Thomas Morgan) began a collaboration on the controversial and unresolved question of how sex is determined in the developing egg. Did external factors, like food and temperature, set the sex of an egg? Or was it something inherent to the egg itself? Or was sex inherited as a Mendelian trait?

She examined the yellow mealworm, Tenebrio melitor, and made a striking observation. She had observed that this species produced two classes of sperm: a type that carried ten large chromosomes, and a type that carried nine large and one small chromosome. Body cells in the females contained 20 large chromosomes while males carried 19 large and one small chromosome.

Stevens reasoned that when an egg is fertilized by a sperm that carries the small chromosome, the result is a male offspring. The presence of the small chromosome might be what decided the individual’s “maleness.”

She published her research in 1905 and it eventually evolved into the XY sex-determination system we know today: The father’s sperm, which can carry either X or Y chromosomes, determines the sex of the offspring. Before Stevens’ work, scientists thought that the mother or the environment determined if a child was born male or female.

Biography

Nettie StevensNettie Maria Stevens was one of the first American women to be recognized for her contribution to science. Yet she didn’t begin her career in genetics until later in life.

Stevens was born on July 7, 1861, in Cavendish, Vermont, to Ephraim and Julia Stevens. After the death of her mother, her father remarried and the family moved to Westford, Massachusetts.

Initially, Stevens taught high school and was a librarian for more than a decade. Her teaching duties included courses in physiology and zoology, as well as mathematics, Latin, and English. Her first career allowed her to save up for college; at the age of 35, she resigned from a high school teaching job in Massachusetts and traveled across the country to enroll at Stanford University in California.

At Stanford, she received her B.A. in 1899 and her M.A. in 1900. She also completed one year of graduate work in physiology under Professor Jenkins and histology and cytology under Professor McFarland.

Stevens continued her studies in cytology at Bryn Mawr College, where she obtained her Ph.D. Here, she was influenced by the work of Edmund Beecher Wilson and by that of his successor, Thomas Hunt Morgan. Her work documented processes that were not researched by Wilson and she used subjects that he later would adopt along with the results of her work.

At age 50 years, only 9 years after completing her Ph.D., Nettie Stevens died of breast cancer on May 4, 1912 in Baltimore, Maryland.

Bring it Home

▶︎ Dive into Genetics with a fun unit study

▶︎ Enjoy a slide show presentation on genetics

▶︎ Learn about the Father of Genetics: Gregor Mendel

▶︎ Try this Gummy Bear Genetics lab from The Science Teacher (a NSTA publication)

▶︎ Use pipecleaners and beads to show how genes and chromosomes are inherited in this Pipecleaner Babies lab.

▶︎ Use pennies to do this How Well Does a Punnet Square Predict the Actual Ratios? lab.

Science Milestones

Visit my Science Milestones page to learn more about scientists whose discoveries and advancements have made a significant difference in our lives or who have advanced our understanding of the world around us.

The bloggers of the iHomeschool Network have teamed up to create fun and original unit studies on fascinating people who were born in July.

 

Science with Harry Potter: Care of Magical Creatures (Zoology)

Care of Magical Creatures is an elective at Hogwarts, available to upper classmen. Throughout the course, students learn about a wide range of magical creatures and are taught about the care and husbandry.

Similar to herbology, the further into a student’s education the more difficult and dangerous the creatures become. The witches and wizards who succeed in the subject later become Magizoologists, like Newt Scamander.

Magical CreaturesFor this class students are required to become familiar with the many magical creatures you may encounter both at Hogwarts and in the outside world. Students should begin with the following:

  • Owl
  • Hippogriff
  • Phoenix
  • Unicorn
  • Werewolf
  • Centaur
  • Basilisk
  • Elf

C’mon, now, get a move on! Got a real treat for yeh today! Great lesson comon’ up! Everyone here? Right, follow me!” ~ Rubeus Hagrid at his first Care of Magical Creatures lesson

Students are required to keep a field notebook in which a two-page spread is created for each magical creature studied. For each magical creature you study:

  1. Make a sketch of the creature, labeling important features
  2. List any historical or literary references to the creature
  3. Describe its natural habitat
  4. Discuss its habits, temperament, and relationship to humans
  5. List its magical properties
  6. Explain the care and feeding of the creature

Advanced students may choose additional magical creatures to study. Take care to choose wisely, as your knowledge of magical creatures could one day prevent a terrible injury or death.

Magical Properties of Dragons

You’ve likely already discovered the magical property of dragon scales while researching and preparing your field notes above. Now you will learn about the properties of dragon skin and dragon down (the fluffy feathers from underneath the wing).

Young wizards and witches should have adult supervision as all parts of a dragon are highly flammable. A fire-proof cauldron is advised.

Dragon Skin: take thin slices of dragon skin and hold them next to an open flame. Bend the skin, squeezing until it bursts. You should see tiny sparks fly as the fire-breathing properties are released. This should be done very close to the flame.

Dragon Down: Put a small quantity of dragon down into a cauldron. Touch the end of a 9 volt battery lightly to the down to release the fire-breathing properties.

(Note to professors: muggles will know these items as orange peel and steel wool.)

Genetics

Students watch a video clip from Harry Potter and the Goblet of Fire to learn about genetic traits. Specifically, they realize that the ability to speak parseltongue (being able to speak to snakes) is a genetic trait possessed by some characters and their parents. Students explore the use of Punnett squares to predict trait inheritance, learning about genotypes and phenotypes.

This post is part of a five-day hopscotch. Join me each day this week as we dive into each course.

Herbology (Botany)

Care of Magical Creatures (Zoology) – this post

Potions (Chemistry)

Alchemy & Divination (Geology)

Magical Motion (Physics)

Science with Harry Potter: Herbology – The study of plants and fungi (Botany)

Herbology is the study of magical and mundane plants and fungi. It is a core class and subject taught at Hogwarts School of Witchcraft and Wizardry for the first five years of a student’s education.

herbology

Herbology

Throughout each term, students learn to care for plants as well as learn about their magical properties and how they may be used medicinally. The further into a student’s education the more difficult and dangerous the plants become.

“Three times a week they went out to the greenhouses behind the castle to study Herbology, with a dumpy little witch called Professor Sprout, where they learned how to take care of strange plants and fungi, and found out what they were used for.” ~ Harry Potter and the Sorcerer’s Stone

All first year students are required to familiarize themselves with the herbs listed below.

  • Chamomile
  • Tarragon
  • Yarrow
  • Caraway
  • Horseradish
  • Dill
  • Aloe Vera
  • Silver Birch
  • Garlic
  • Tumeric

herbologyAs students work through their self-guided journey, they are required to keep a field notebook in which a two-page spread is created for each plant or fungi studied. Each spread is required to include the following information:

  1. Give common name as well as Latin names (genus and species) and family
  2. Press a specimen of the plant (if possible)
  3. Make a sketch of the plant, colored appropriately
  4. Label key parts of the plant, pointing out important features
  5. Explain its cultivation and care
  6. Give a brief natural history of the plant (describe growth cycle, natural range, etc.)
  7. List its household and medicinal uses both presently and historically
  8. Describe its magical properties (if any)

Take it Further

Enjoy a cup of Chamomile tea before bedtime or a glass of birch beer with your noonday meal.

Explore the many wildcrafting and herbal remedies described at Learning Herbs.

Enjoy the fun board game, Wildcraft: An Herbal Adventure.

Research the native plants in your local area and learn how native peoples used them for food and medicine.

Visit a native elder, if possible, and learn to how to harvest and prepare these plants for personal use.

As you advance in your studies, be sure to add each new plant to your journal.

This post is part of a five-day hopscotch. Join me each day this week as we dive into each course.

Herbology (Botany) – this post

Care of Magical Creatures (Zoology)

Potions (Chemistry)

Alchemy & Divination (Geology)

Magical Motion (Physics)

Problem Based Learning with William & Mary

This past school year, my kids and I have been inundated in the study of coastal ecology. The kids worked through the curriculum along side me. Memorizing vocabulary and understand the ecology concepts came easily to them as I’ve immersed them in nature studies since they were toddlers.

We enjoyed several memorable field trips whereupon we developed a list of questions based on our observations: Roosevelt Elk at Dean’s Creek & Foraging for Mushrooms.

We also engaged in several nature study investigations to learn more about the organisms we had observed: Slugs, Snails, and Sea Hares Our Native Maple Trees.

I received this product for free and am being compensated for the time to write the review.  This is an honest review of the product.problem based learning

Yet all along, I knew in my heart that something was missing. While they were engaged in our lessons and activities, they were not captivated. I wanted them to be challenged. I wanted them to struggle to find answers to their questions. I wanted a problem based learning experience.

The units created by William & Mary from Kendall Hunt Publishing provide the perfect challenge. The books provide a wonderful framework for getting students to think, presented in such a way that they want to solve the problem. Along the way, students experience the processes and tools a scientist may use when presented with a difficult problem.

What is Problem Based Learning?

Problem Based Learning is a student-centered pedagogy in which students learn about a subject through the experience of solving an open-ended problem. Students gain content knowledge and develop skills by working for an extended period of time to investigate and respond to an engaging and complex question, problem, or challenge.

When I was given the opportunity to review the William & Mary problem based learning materials, I immediately jumped at the chance. The Animal Populations unit (designed for grades 6-8) was the perfect fit to further our understanding of ecology and wildlife sciences.

william & mary

Problem Based Science Units by William & Mary 

The William & Mary science units introduce real-world problems to initiate scientific investigations. All units incorporate a problem based learning scenario as the catalyst for initiating the discussion of content and scientific investigation.

Students not only focus on specific content learning in science, but they also develop scientific investigation skills as a way to develop the thinking skills of a scientist. Students pose questions, then conduct experiments to answer those questions. They also identify independent and dependent variables, constants, and controls as a guide for quality investigations.

Animal Populations Unit

Animal Populations is centered around the problem of a growing population of deer in a fictitious rural community and the increasing number of people afflicted with lyme disease. The story begins with an email a mother writes to her spouse relaying the symptoms their son has developed.

Immediately, both kids were intrigued and were searching for possible causes. As the story unfolded with newspaper articles and additional personal accounts, they began to collaborate to find solutions to the problem.

In addition to staging the problem, the lessons lead students through the process of inquiry and experimental design. Each step is clearly outlined and in context with the big picture or ecology. We started each lesson with a discussion on the vocabulary and review of where we left off in our previous lesson.

I was really impressed with the lessons on the concept of models. While we are all familiar with physical models, the lessons clarified the meaning of conceptual and mathematical models in-depth. The lessons built on each other and really helped the kids (myself included!) understand the mathematical models of a deer population: exponential growth model and logistic growth model.

deer populationsOur favorite lessons were the field studies whereby we implemented a transect survey. We were fortunate at the time we implemented this unit to be able to partner with a local agency to take part in an ongoing bio-monitoring project at the national estuarine research reserve. Not only was our data useful in the context of our lesson but it was also critical for the success of their long-term estuarine research.

We all enjoyed this unit study as it was both challenging and fun. I look forward to implementing more problem based units in the near future.

Other Science Units

Kendall Hunt Publishing offers several other William & Mary science units to choose from, several have received National Association for Gifted Children’s Curriculum Studies awards.

* Where’s the Beach?—Grades 2-4 
* What A Find!—Grades 2-4  (See Erin’s review at Royal Baloo)
* Acid, Acid Everywhere—Grades 4-6
* Electricity City—Grades 4-6
* Nuclear Energy: Friend or Foe?—Grades 6-8
* Something Fishy—Grades 6-8
* No Quick Fix—Grades 6-8

Unit content has been aligned to national standards and meets national grade level standards as well as standards for grades that are two to three levels above the current grade.

Connect with Kendall Hunt

Follow Kendall Hunt Publishing on your favorite social media. By connecting with them you will get regular updates, information about their products, encouragement for teaching gifted learners as well tips and ideas.

Sea Slugs, Snails, and Sea Hares, Oh My!

I love slugs! They are one of my favorite animals, particularly if limiting the scope of the question to invertebrates. In my opinion, they are one of the most beautiful and fascinating organisms.

You’re likely thinking I have lost my mind. “You really think this guy is beautiful?” 

Sea Slugs, Snails, and Sea Hares

Pictured here is the banana slug

Yes, I do. Well, actually, in my mind I was picturing his close relative the sea slug or nudibranch. This summer, I have been volunteering at the new Marine Life Center at the Oregon Institute of Marine Biology and I’ve thereby had the opportunity to learn so much about these fascinating animals. Let me introduce you to the gastropods.

Class Gastropoda 

The Gastropoda or gastropods class, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. A very diverse group with 60,000 to 80,000 living species (second only to insects in number of species) that includes snails and slugs of all kinds and all sizes from microscopic to large. There are many thousands of species of sea snails and sea slugs, as well as freshwater snails, freshwater limpets, land snails and land slugs.

Sea Slugs, Snails, and Sea Hares @EvaVarga.net

How many sea slugs can you find in this picture?

The anatomy, behavior, feeding, and reproductive adaptations of gastropods vary significantly from one group to another. The class also inhabits an extraordinary diverse habitats including gardens, woodland, deserts, mountains, rivers and lakes, estuaries, mudflats, the rocky intertidal, the sandy sub-tidal, the abyssal depths of the oceans including the hydrothermal vents, and numerous other ecological niches, including parasitic ones.

Sea Slugs, Snails, and Sea Hares @EvaVarga.net

Gastropoda means the belly-foot animals

Snails & Other Shelled Gastropods

Commonly, snails are those species with a single external shell large enough that the soft parts can withdraw completely into it. Those with a shell into which they cannot withdraw are termed limpets.

The marine shelled species of gastropod include species such as abalone, conches, cowries, periwinkles, whelks, and numerous other sea snails. Each produce seashells that are coiled in the adult stage. In a number of families of species, such as all the various limpets, the shell is coiled only in the larval stage, and is a simple conical structure after that.

Sea Slugs, Snails, and Sea Hares @EvaVarga.net

Pictured here is Hermissenda crassicornis

Slugs or Gastropods Without External Shells

Those gastropods without a shell, and those with only a very reduced or internal shell, are usually known as slugs. The various families of slugs are not closely related, however, despite a superficial similarity in the overall body form.

Sea Slugs

The phrase “sea slug” is perhaps most often applied to nudibranchs and they come in an outstanding variety of shapes, colors, and sizes. With translucent bodies, they appear in just about every color on the rainbow. Of course, these bright colors are cause for warning to potential predators that they are poisonous with stinging cells. It is their colors that so fascinate me.

Like all gastropods, they have razor-sharp teeth, called radulas. Most have two pairs of tentacles on their head used primarily for sense of smell, with a small eye at the base of each tentacle. Many have feathery structures (ceratia) on the back, often in a contrasting color. These act as gills.

All species of sea slugs have a selected prey, that is specifically fitted for them to hunt. Amongst the diverse prey are jellyfish, bryozoans, sea anemones, sponges, and other various organisms including other sea slugs.

Sea Slugs, Snails, and Sea Hares @EvaVarga.net

Pictured here is Phyllaplysia taylori

Sea Hares

The sea hares, clade Aplysiomorpha, are often quite large and sometimes described as large sea slugs. They have a small, flat, internal shell composed of proteins. The name derives from their rounded shape and from the two long rhinophores that project upwards from their heads and that somewhat resemble the ears of a hare.

The greatly modified shape of the sea hare and the fact that it orients its body lengthwise along the leaves makes it almost invisible on the sea grass Zostera. An herbivore, it feeds by grazing the film of organisms, mainly diatoms, off sea grass leaves, leaving a characteristic feeding scar on the leaves.

Take it Further

Learn more about Phyla Mollusca in my earlier post, Echinoderms and Molluscs.  You might also be interested in my in-depth zoology curriculum specifically designed for middle school students.

zoology

Getting Creative with iDO 3D Art Pens

My daughter has always loved anything related to arts and handcrafts. Even as a toddler she would spend hours drawing and making gifts for her family with my craft supplies. It is no wonder that art is one of her strongest passions. She has wanted to try 3D art pens for some time and was delighted to learn I would have the opportunity to review the IDO3D for my readers.

As a family, we have been volunteering regularly at the new marine life center and have made several field trips to a variety of coastal habitats to learn more about the local ecology. When the IDO3D art pen arrived, she knew immediately what she wanted to create … jellyfish.

3D Art Pens

Disclosure: I was compensated for my time reviewing this product and for writing this review.

IDO 3D Art Pens

The IDO3D comes with four pens (or color cartridges): blue, green, red, and yellow. Each pen has a safety seal or cap that will need to be removed. Thereafter you will twist on the cap. Lastly, you snap the blue spotlight holder into place (it clicks into place).

There are instructions on how to use the 3D art pens provided as well as helpful tips and tricks detailed in a short video. I was very impressed with how quickly we got the hang of it. Granted, our lines are a little wobbly and jiggly but as they say in the video, “Practice and patience are the key.”

3D Art Pens

Creating Jellyfish with 3D Art Pens

Using my invertebrate zoology textbook as a reference for jellyfish anatomy, she was underway within just a few minutes. One of the materials in the box was a plastic sheet shaped like a bowl which she used to begin her project; creating the exumbrella inversely. She chose blue ink for this part – though she also opted not to fill in the connecting space as she wasn’t sure if she would have enough ink.

Once it had cured, she proceeded to create the internal anatomy with green ink: mouth, gastrovascular cavity, gonads, and oral arms. She discovered, however, that the space was too confined for the spotlight and she wasn’t able to add all the parts she would have liked. “I probably would approach it a little differently next time,” she stated. “I think I should have created the internal parts separately and then attached them later.”

Lastly, she began to add the tentacles and worked vertically as she did so. This proved to be the most challenging part of the process. As they were so long and thin, they kept leaning in one direction or another rather than staying vertical. Like any art medium, she recognizes that it takes practice and patience.

“I really like this pen. It is easy to use and I can create something right away. Perhaps the jellyfish was too complicated for my first project.”

3D Art Pens

Classes & Projects for IDO 3D Art Pens

We look forward to creating a variety of projects with the IDO3D art pen. There are also several 3D Art Classes from which to choose. When my son saw the following video he said,

“You can do all that?! That’s so cool!”

Where to Buy IDO 3D Art Pens

The IDO3D art pen is available from a variety of retailers nationwide. It is also available on Amazon.

For ideas and inspiration for projects, I encourage you to follow IDO3D on Facebook, Pinterest, Twitter, and YouTube.