Every Day Is Special: reproduction

Showing posts with label reproduction. Show all posts

July 7 - Happy Birthday, Nettie Stevens

Posted on July 7, 2022

This is an update of my post published on July 7, 2011:

Most famous for her discovery of the chromosomal difference that (usually) determines whether an animal is male or female, Nettie Stevens is one of the first American women actually recognized for her contribution to science!

Nettie Stevens was born in Vermont on this day in 1861. She studied at Westfield Normal School in Massachusetts, graduating at the top of her class, and she earned B.A. and M.A. Degrees from Stanford University, in California. Finally, at Bryn Mawr (in Pennsylvania), Stevens studied insects and was able to identify the Y chromosome in a species of mealworms. She completed her PhD at Bryn Mawr in 1903.

This is Nettie Stevens pictured with X (above)
and Y (below) chromosomes.

You might know that most mammals have two sex chromosomes. Oversimplifying a bit, males have one X and one Y chromosome, and females have two X chromosomes. (That's an oversimplification because, first, there are individuals who have only one sex chromosome and others who have three; second, there are some conditions in which individuals with XY chromosomes develop female reproductive structures and individuals with XX develop male reproductive structures. Add to all of that the fact that, in humans at least, there is a wider range of gender identity than just male/female.)

Getting back to animals' sex chromosomes: although some insects such as fruit flies also have X and Y chromosomes, many animals do not have sex chromosomes. In some cases a creature's sex is determined by the environment. For example, if an egg is kept at one particular temperature, the developing creature becomes male; at another temperature, the creature develops into a female.

Some animals (about one third of all animal species, other than insects) have both male and female gametes and are either born male, later becoming female if necessary, or vice versa. Clownfish like Nemo fall into this category. Also, most plants are hermaphrodites.

Of course, some organisms are asexual - they don't have sexes at all.

An example of asexual reproduction:
a hydra budding off a "baby" hydra.

Also on this date:

Running of the Bulls in Spain

Figure skater Michele Kwan's birthday

Musician Ringo Starr's birthday

Independence Day for the Solomon Islands

Saba Saba Day in Tanzania

Anniversary of Olivier Levasseur giving the world a challenge

Unity Day in Yemen

Tell the Truth Day

Tanabata Matsuri (Star Festival) in Japan

Plan ahead:

Check out my Pinterest boards for:
July holidays
July birthdays
Historical anniversaries in July

And here are my Pinterest boards for:

August holidays
August birthdays
Historical anniversaries in August

July 23 - Cloning Success!

Posted on July 23, 2021

This is an update of my post published on July 23, 2010:

On this date in 1998 the “Yana team” (Ryuzo Yanagimachi and his research team from the University of Hawaii) published about their new technique for cloning mammals from adult cells. The team cloned more than 50 identical mice representing three different generations. The paper was published in the respected journal Nature.

Dolly the sheep, the first mammal successfully cloned,
is perhaps the most famous clone as well.

Many plants and most animals reproduce sexually, which means that a male fish and a female fish together produce baby fish, male birds and female birds together make fertilized eggs, male plant parts and female plant parts work together to create seeds, and so forth. In sexual reproduction, there are two parents, each passing on half of his or her genetic material, and so almost every baby plant or animal ends up being unique. (Of course there are exceptions such as identical twins.)

Some organisms reproduce asexually. Bacteria, protists, many fungi and plants, and some animals are able to create offspring with just one parent―and the offspring has pretty much the same genes as that parent. (Again, there are exceptions such as mutation and “lateral gene transfer.”)

Cloning is a lot like asexual reproduction. Generally speaking, genetic material (inside a nucleus) is taken from a single individual and is inserted into an egg that has no nucleus. If the cell begins dividing, it is transferred to a surrogate mother. Another artificial cloning method involves deliberately creating identical twins by dividing a cell at a crucial state of development―and both pieces go on to create identical organisms.

There is a lot of controversy over cloning―especially over cloning humans―but actually farmers and gardeners have been cloning plants for centuries or even millennia! One could say that it is unfair to use the word cloning for processes such as grafting, but the word was used in horticulture first!