Tag Archives: genetics

How These All-Female Lizards Are Able to Reproduce and Thrive Without the Help of Any Males

As far back as the 1960s, scientists were aware that a number of whiptail lizards in Mexico and the southwestern United States were made up entirely of females.

The most notable of these species, the New Mexico whiptail lizard, is able to reproduce healthy, well-bred offspring without the aid of male fertilization.

Whiptails aren’t the only species that reproduce asexually. In fact, there are 70 other vertebrate species that can do it. But the New Mexico whiptail may have unlocked the secret as to how it’s possible for a species that produces exclusively asexually to thrive.

Komodo dragons are among the vertebrate species that are able to reproduce asexually

Peter Baumann works at the Stowers Institute for Medical Research in Kansas City, Missouri. He co-authored a study on the lizards that was published in the journal Nature back in 2010.

Baumann explains that parthenogenteic species (species that reproduce without fertilization), are genetically isolated because they only inherit the DNA of one parent.

This means that any genetic weaknesses, like susceptibility to a disease or physical mutation, can’t be “overridden” by healthy genes from a second parent. The shallower the gene pool, the more likely it is to produce sick or mutated offspring.

To deal with this issue, the all-female whiptail lizard species have evolved to start the reproductive process with twice as many chromosomes as their sexually-producing lizard relatives.

New Mexico whiptail lizards were actually the result of two different species of lizard (the western whiptail and little striped whiptail) interbreeding to form a hybrid species. Because of this, these all-female lizards are equipped with a very diverse gene pool.

Left: little striped whiptail. Middle: New Mexico whiptail. Right: tiger whiptail. Click to enlarge

Instead of combining homologous chromosomes (like sexual species do, getting one set from each parent), the lizards pair recombined sister chromosomes instead. This maintains heterozygosity in the offspring.

Here’s a more simple way to think about it. Every one one us has DNA from generations and generations of our ancestors. When we reproduce, we combine our DNA with our partner’s- the resulting offspring’s genetic codes contains parts of both parents’ DNA.

But since we have such vast genetic diversity from all of our ancestors, the exact coding of the genes we pass along when we reproduce isn’t always the same, which is why brothers and sisters don’t all look the same.

A basic way to visualize how genetic information is passed on in sexual reproduction. Note that the “marbles” passed on by each individual parent are different for the two children. Click to enlarge

So, rather than combining its genetic code with that of a male, the whiptail lizard combines two different versions of its own DNA code, ensuring that each pairing of sister chromosomes will have multiple alleles (different forms of a gene), which gives the offspring the genetic diversity it needs to be healthy.

This discovery means that,

“these lizards have a way of distinguishing sister from homologous chromosomes,”

says Baumann. How do they do this? The researchers aren’t sure yet, but it’s the next question they will be investigating, along with the question of how they evolved to start reproduction with double the normal amount of chromosomes.

Female whiptail lizards perform courtship rituals with one another to stimulate ovulation. The top lizard will lay smaller eggs while the one on the bottom will lay larger eggs. They switch spots every mating season. Click to enlarge

Though it may seem like asexual reproduction would eventually hurt a species in the long run, Baumann also pointed that,

“You’re greatly increasing the chances of populating a new habitat if it only takes one individual.”

It seems to be working pretty well for these lizard ladies.

Read the original story from the Scientific American here.

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San Men of the Kalahari Show What A “Fair Chase” Hunt REALLY Looks Like (Video)

Earlier today, I discussed the controversy surrounding Kendall Jones, a 19-year-old Texas Tech leader who hunts big game in Africa and posts the pictures to Facebook.

In the caption of a picture of her with an African leopard, Kendall described the hunt as a “fair chase”. I feel the need to disambiguate that term.

Let me present the San people of the Kalahari desert in Africa. This traditional hunter-gatherer society inhabits the Kalahari Desert in southern Africa. San men go on marathons across the desert to track down the Kudu antelope which provide key protein for their families:

The San people lived as hunter-gatherers for countless generations until government modernization programs, lasting from the 1950s until the 1990s, mandated that many of the San switch to farming.

They are one of our fourteen surviving “ancestral population clusters” from which all modern humans today descend from. Studies of the San have provided a wealth of information in the fields of anthropology and genetics.

So let’s be clear: hunting  with high-powered rifles and motorized vehicles is as far from a “fair chase” as it gets.

New Discovery: HIV Can “Cut and Paste” In Our Genome, Allowing Us To Use It to Repair Genetic Conditions

Researchers in the Department of Biomedicine at Aarhus University in Denmark just did something truly amazing: they altered particles of the HIV virus to simultaneously “cut and paste” within our genome. Here’s Jacob Giehm Mikkelsen, associate genetics professor at Aarhus:

“Now we can simultaneously cut out the part of the genome that is broken in sick cells, and patch the gap that arises in the genetic information which we have removed from the genome. The new aspect here is that we can bring the scissors and the patch together in the HIV particles in a fashion that no one else has done before.”

The technology will allow doctors to repair the human genome in a new way, and will also be invaluable in the treatment of hereditary and viral diseases as well.

HIV particles (yellow) infecting a human T-cell (Image: NIAID/NIH)

The cutting and pasting process isn’t actually a new one- we have been able to “cut and paste” parts of the genome using cells for a while now. The problem with this process, however, is that these cells would keep producing more “scissors”. Mikkelson explains,

“In the past, the gene for the scissors has been transferred to the cells, which is dangerous because the cell keeps on producing scissors which can start cutting uncontrollably. But because we make the scissors in the form of a protein, they only cut for a few hours, after which they are broken down. And we ensure that the virus particle also brings along a small piece of genetic material to patch the hole… We call this a ‘hit-and-run’ technique because the process is fast and leaves no traces.”

We have known for years that HIV particles can be turned into transporters of genetic information. However, this new discovery that they can also be altered to carry proteins that can have a direct effect on infected cells, rather than just on the genes, is huge.

Artist rendition of the HIV virus (Image: Russel Kightley)

Ironically enough, HIV infection is one of the main fields in which the researchers plan to employ this new process. Here’s post-doctoral professor Yujia Cai, who was also part of the research team:

“By altering relevant cells in the immune system (T cells) we can make them resistant to HIV infection and perhaps even at the same time also equip them with genes that help fight HIV. So in this way HIV can in time become a tool in the fight against HIV.”

Read more from Aarhus University News here.

How Unemployment Is Literally Shortening Men’s Lives

A team of researchers from the Imperial College of London and the University of Oulu in Finland recently conducted a study where they examined the DNA of 5,620 men and women born in Finland in 1966.

The researchers were measuring the subjects’ telomeres. Telomeres are the structures at the ends of our chromosomes which protect our genetic code. They naturally wear away and shorten as we age, so scientists are able to use them as a biological marker for aging.

Telomeres and DNA structure

The researchers examined DNA samples from 1997 when the subjects were all 31. What they found was that men who had been unemployed for more than 2 of the 3 years before the samples were taken were more than twice as likely to have shorter telomeres compared to men who were employed continuously.

The study also accounted for a number of other, “social, biological and behavioural factors” to rule out the possibility that the short telomeres were a result of other causes.

This trend was not observed in the women in the study, however.

Read the full story here.