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)

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.

Wildlife Biology for Middle School: Develop Skills with Animal Cams

animalbehaviorWildlife Biologists are scientists that observe and study the behaviors of animals. They frequently observe the features of certain wildlife and determine the role these animals have in their specific ecosystems. Many Wildlife Biologists specialize into a particular area of study defined by ecosystem or species. Some of these fields include: Entomology (insects), Ichthyology (fish), Ornithology (birds), or Marine Biology.

Youth interested in learning more about animals and the study of wildlife can learn a great deal from the comfort of their home via a webcam. Though limited in scope, animal cams can provide a glimpse into the lives of animals and are one tool to help develop our understanding of animal behavior.

I have compiled a list of some of my favorite animal cams from around the world. Take time to browse them all or utilize the printables I’ve provided below to develop a more in-depth wildlife biology study on your favorite animal.

ethologyOur Favorite Animal Cams

Birds

Bald Eagles

Location: Decorah, Iowa
Best time to watch: Eggs may begin hatching between March 25 and March 29 based on a 35 to 39 day incubation period.

The Decorah bald eagles nest atop a large white oak tree in a secluded valley. Their eggs hatch roughly 35 days after they are first laid, which means that three eggs within the nest right now are due any time now.

Location: Turtle Bay Eagle Cam (Redding, California)

We became captivated by this breeding pair when we first moved to Redding in 2011. The female Bald eagle has successfully fledged 14 eaglets and in 2015 had 3 youngsters in the nest!  This is not the first time she has done this, as she did the same in 2009 and 2010.  Only 5% of Bald eagles successfully lay and fledge three eaglets. Though this animal cam is currently offline (the eagle pair have moved), their story is fascinating.

Hummingbirds

Location: La Verne, California
Best time to watch: March (chicks are hatching any minute)

Bella the Hummingbird has been nesting for more than 10 years. Her nest is about the size of a golf ball, and her eggs are only about the size of a mint. Every spring she lays eggs and a couple weeks later the world watches new life being born. This year, she last laid her eggs on the 6th and 8th of March. When I checked in with her as I wrote this post, they’d recently hatched.

Great Horned Owls

Location: Montana
When will you see babies? Due in roughly 2-3 weeks.

The Montana owlets are due two or three weeks from now. Since owls are nocturnal, this is a live feed worth checking out later at night when the other animal cams have little or no activity.

Spotted Owls

Location: High Desert Museum (Bend, Oregon)

When we lived in Bend, the spotted owl pair at the High Desert Museum were receiving a lot of media attention. It had previously been believed that Spotted Owls required old growth forest to survive yet here were a rehabilitated pair who had successfully reared several consecutive clutches of chicks. Sadly, I believe the owl cam is presently offline.

Penguins

Location: Aquarium of the Pacific (Long Beach, California)
Best time to watch: All the time.

The above the water cam shows the edge of the rocky beach, where penguins hop in and out of the water. You can watch as they swim and float on the surface. They also have a below the water cam to view the penguins as they dive and dart below the surface.

Mammals

Bears

Location: Katmai National Park, Alaska
Best time to watch: In July when their babies are born.

A mama bear and her three bear cubs is what you’ll get if you tune into the Brooks Falls animal cam, which features big shaggy brown bears catching fish, wading around, and just generally having a good time in Alaska’s Katmai National Park. Since bear cubs are only due in July, this cam currently hosts a continual stream of highlights gathered from several live cams.

Manatees

Location: Blue Spring State Park (Maitland, Florida)
Best time to watch: Winter and early Spring
We first discovered the Save the Manatees Club when we were planning a family holiday to the Florida Keys. Though the manatee season has ended, favorite clips are still accessible. The live cams will resume again next season.

Sea Otters

Location: Monterey Bay Aquarium (Monterey, California)

You can watch sea otters here from 7 a.m. to 7 p.m. Pacific Time. Daily feeding times are 10:30 a.m., 1:30 p.m., 3:30 p.m. And who knows? Maybe you’ll spot an otter pup somewhere in there.

Sloths

Location: Atlanta, Georgia

This sloth cam, part of Zoo Atlanta, lets you become virtual best friends with two-toed sloth Cocoa, his lady friends Okra and Bonnie, and baby sloth Raisin. Though it’s currently offline, you can still log in at 1:30 pm ET every other Wednesday for sloth chats.

Reindeer

Location: “North Pole”
Best time to watch: Holiday season
Reindeer who aren’t employed by St. Nick live in the colder climates of North America and Europe where they feast on a diet of moss, leaves, and grass. They are sometimes referred to as Caribou in Canada.

Fish

Sea Dragons

Location: Aquarium of the Pacific (Los Beach, California)

Found only in Australian coastal waters, Sea Dragons are bony fish related to seahorses, pipefish, and seamoths.

Invertebrates

Jellyfish

Location: Aquarium of the Pacific (Los Beach, California)

Few things are more calming than watching these serene, colorful jellyfish float their lives away.

Ecosystems

Kelp Forest

Location: Monterey Bay Aquarium (Monterey, California)

Watch this underwater kelp forest cam to see an astonishing array of diverse fish and invertebrates. If you’re lucky, you’ll see a wolf-eel chow down on a squid or some fish.

Coral Reef

Location: National Aquarium (Baltimore, MD)

African Savanna

Mpala Live – Meet the animals that roam Mpala in Kenya’s Laikipia area. Their website also provides field guides, lesson plans, and activities that you can download free to get more out of your viewing.

~ ~ ~

For a comprehensive collection of animal webcams, visit Live Animals TV, the world’s largest collection of animal webcams.

wildlifebiologyWildlife Biology Lesson Plans & Printables

I have put together a simplified ethogram or inventory of behaviors and actions exhibited by an animal. The free printable will be available for my newsletter subscribers later this week. Take a moment to subscribe today. It will be available only for a limited time.

Most aquariums, zoos, and wildlife centers around the country have developed activity guides and animal observation lessons. You’ll find curriculum and materials for many of the animal cams shared above at the original host site. Many of these can be modified for use with animal cams as well as during your site visit. Browse their education links to see what you can find.

e·thol·o·gy
noun: ethology
  1. the science of animal behavior.
    • the study of human behavior and social organization from a biological perspective.

The Lincoln Park Zoo in Chicago, Illinois provides a wonderful Zoo Observation Data Sheet whereby students use an ethogram-based data sheet to record animal behavior. Thereafter, students use the data they have collected to develop their own animal behavior research project. Their materials can be adapted to wildlife viewing locations around the world.

You may also wish to download this very informative Animal Behavior slide show presentation to become familiar with the range of animal behavior and understand the methods that ethologists use to study animal behavior.

 

Agriculture in the Classroom: Free Teaching Resources

As we become for technologically advanced and our urban cities grow, I believe it is increasingly important for our youth to have an understanding of where our food comes from – both historically and today.

Whether you live in Atlanta or rural Nebraska, in the mountains or along the coast, engaging students in real world experiences and developing an awareness of agricultural practices is not difficult. There are many free teaching resources available for educators of all ages.

By encouraging teachers to integrate agriculture into their classroom via authentic, core curriculum concepts, Agriculture in the Classroom partners have collaborated to cultivate an understanding and appreciation of the food and fiber system that we all rely on every day.

classroomagriculture

An agriculturally literate person is defined as “one who understands and can communicate the source and value of agriculture as it affects our quality of life.”

Take some time to explore the variety of resources available – I share a few of my favorites below. You can put together an entire semester course or pick and choose a few lessons to augment your current studies.

 

Plant & Animal Science

Agriculture has traditionally been defined by the production of plants and animals. Today, science and technology have added new areas of research, and investigation to the agriculture field.

agricultureExtension 4-H professionals have developed a wealth of curriculum materials and a variety of hands-on agriculturally based activities to promote agricultural literacy among young people. Much is available for free but some curriculum modules are available for purchase.

Soil Science

To help educate students about the important role soil nutrients play in feeding our world, the Nutrients for Life Foundation sends out a monthly newsletter that will provide you with new ideas and tips for teaching plant and soil science while providing creative activities to bring into your classroom. They have also developed numerous modules for elementary, middle and high school classrooms to provide STEM activities and lessons.

soilscienceSoil Science Reader :: A digital science journal specifically designed for grades 7-8 (graphics and photographs capture interest) introduces soil formation and soil horizons with a fun edible soil activity. Other topics include the nitrogen cycle, plant nutrition, and fertilizer basics featuring the 4R Nutrient Stewardship.

Soil Reader :: Written specifically 5th & 6th grade students, this 18-page digital journal features an interview with an agriculture engineer and features puzzles, quizzes, and visuals to enhance a teacher’s soil unit.

For complete curriculum, posters, games, flashcards, and much more – visit the Nutrients For Life webstore. Everything is FREE!!

Invasive Species

Hundreds of invasive plants and animals have become established across the country and are rapidly spreading each year. These invaders are negatively impacting our waters, our native plants and animals, our agriculture, our health, our economy, and our favorite recreational places.

Prevention is the most effective strategy in managing invasive species. To increase public awareness of invasive species issues and promote public participation in the fight against invasive species and their impacts on our natural resources, the California Department of Fish & Wildlife have developed curriculum and materials available free to schools and educators.invasivespecies

Stop the Invasion :: Students will learn about six different invasive species, the damage they cause, and how to stop their spread.

If you reside in California, you may also be interested in the community action week with events across the state and a youth art contest. Similar programs may exist in your state. Contact your local department of fish and wildlife or county extension agency to learn more.

Our Native Maple Trees: A Nature Study

Though we are in the middle of winter, we’ve been immersed in a study of maple trees. A few weeks ago, I shared a post relaying the science of sugaring.

The United States has 13 native maples, with at least one species native to every state except Hawaii. I’ve selected seven to highlight today – with particular attention to the species native to Oregon.

Our Native Maple Trees @EvaVarga.netGenus Acer

Maple trees are classified in the genus Acer in the Maple family (Aceraceae) and nearly all of the species are deciduous. Three traits that can help you identify a maple tree are:

* Leaves palmate and lobed (for most species),

* Opposite branching, and

* Winged seeds called samaras.

Acer trees and shrubs are commonly known as maple. There are approximately 128 species, most of which are native to Asia, with a number also appearing in Europe, northern Africa, and North America.

Acer saccharum

The Sugar Maple (Acer saccharum) is one of America’s best-loved trees. In fact, due to its historical and economical importance (both in the production of maple syrup and as a timber species), more states have claimed it as their state tree than any other single species (New York, West Virginia, Wisconsin, and Vermont).

The simple leaves of Sugar Maple measure from 3 to 5 inches long and are in an opposite arrangement on the twigs. They are usually five-lobed, dark green on the top surface and paler underneath. They are generally smooth on both sides, although the veins underneath may be slightly hairy.

Acer nigrum

Black Maple (Acer nigrum) is a species of maple closely related to A. saccharum and treated as a subspecies of it by some taxonomists. Identification can be confusing due to the tendency of the two species to form hybrids and to share habit, range, and quality and use of wood.

BigLeafMaple*Acer macrophyllum*

Bigleaf Maple (Acer macrophyllum) is native to the Pacific Northwest and grows in mountainous regions. It is widespread in the Coast Ranges, the Klamath-Siskiyou Mountains, and the foothills of the Cascade Range and the northern Sierra Nevada. It is also commonly known as Oregon Maple for its prevalence in our state.

The deeply lobed leaves are generally 6-12″ in diameter but have been known to exceed this in favorable conditions. The samaras have a fuzzy head, unlike the other species in Oregon.

*Acer circinatum*

One of the most beautiful sights in our woods and forests has got to be the native Vine Maple (Acer circinatum). Found as an under story plant to tall evergreens, from southern BC to northern California and east to the Cascades, Vine Maple is a hardy species.

This elegant tree grows quickly to 10-15′ with multiple trunks and spreads to 20′ widths, much like a vine. Brilliant red and orange colors signal the arrival of autumn, while showy white flowers appear in early spring. It features 3-5 lobes and smooth-headed samaras that grow in a “V” shape.

*Acer glabrum*

Douglas Maple (sometimes referred to as Rocky Mountain Maple) is native to both sides of the Cascades, from southeastern Alaska to southwestern Alberta and south into New Mexico and California.

Its leaves feature 7-9 lobes, easily distinguishable form its close relative the Vine Maple. Hardier than Vine Maple, this tree is often multi-stemmed, with greenish-yellow flowers, and samaras that are oriented in a “V” shape.

Our Native Maple Trees @EvaVarga.netAcer saccharinum

Native to eastern and central North America, Silver Maple (Acer saccharinum) gets its name from the silvery undersides of its leaves. The simple, palmately veined leaves are 3–6″ long and 2–6″ broad, with deep angular notches between the five lobes. With slender leaf stems, a light breeze can produce a striking effect as the downy silver undersides of the leaves are exposed. 

The winged seeds or samaras are the largest of any of the native maple. They are produced in great abundance annually, providing many birds and small mammals with food. Silver Maple and its close cousin Red Maple (with which it can hybridize) are the only Acer species which produce their fruit crop in spring instead of fall.

Acer rubrum

Red Maple (Acer rubrum) is one of the most common and widespread deciduous trees of eastern and central North America. One of the best named of all trees, it features something red in each of the seasons—buds in winter, flowers in spring, leafstalks in summer, and brilliant foliage in autumn.

Produces red (sometimes yellow) clusters of small flowers winter to spring and features medium to dark green leaves 2–6″ in length with 3 lobes and sinuses that are irregularly toothed.

 * * *

Other Maple species found throughout the United States include Ashleaf or Boxelder Maple (Acer negundo), Canyon or Bigtooth maple (Acer grandidentatum), and Striped Maple (Acer pensylvanicum).

Sugaring?

But are Sugar Maples the only trees that can be tapped to produce maple sugar? This is a question that has long intrigued my father. Together, we’ve undertaken an investigation to discover the answer for ourselves.

Join me again in a few weeks as I share with you our own experiences in tapping maple trees on the Oregon coast.

 

 

*Acer species found in Oregon