Diverse findings emerge during the study of molecular traits: from the surprising family relationship between the whale and the hippopotamus to the future takeover of the gene for Tay-Sachs disease on the ultra-Orthodox Ashkenazi
Prof. Graor. "There are molecular biologists who wouldn't recognize a whale even if it fell on them, but any biologist can put a whale's DNA on the computer screen"
Photo: Ariel Shalit
The whale is the largest animal in nature, and its lifestyle arouses special curiosity in humans. Jonah the prophet was not swallowed by an octopus, nor was Pinocchio, and perhaps it is no coincidence that one of the greatest novels in the history of literature describes the struggle between a sea captain and a whale. Man may be perceived as ruling the land, but in the ocean the whale is in front of you.
60 million years ago, the ancestors of the whale roamed across the continents, like any other land mammal. For unclear reasons, the whale chose to return to the ocean, and the extent of his family relationship to the mammals remaining on land remained a mystery until recent times.
Charles Darwin assumed that there was a common ancestor for all animals, and one of the challenges facing evolutionists is assembling the family tree of the animal world. The construction of the family tree is based on the degree of kinship between animals, and it requires researchers to discover the approximate time during evolution when two animals turned to different paths of development.
Traditional evolutionists studied the anatomical structure of animals, and the degree of kinship between animals was determined by the degree of structural similarity between them. The traditional school failed to identify the relatives of the whale, mainly because the whale has features that have no equivalent in other mammals. The whale, for example, does not have a pair of hind legs, and attempts to find similarities between its anatomy and the anatomy of other mammals have not borne fruit.
The competing school of thought began twenty years ago, and includes mainly molecular biologists and geneticists. These researchers do not pay much attention to the structure of the animal and choose to focus on its genetic material and proteins. "Molecular biologists recognize the fact that there may be a contradiction between the hereditary material and the external appearance of an animal," says Prof. Dan Graor from Tel Aviv University. "When we try to build a family tree of animals, the important figure is the degree of similarity between the genetic material and the proteins of a certain animal and those of another animal." For example, the external appearance of the chimpanzee is similar to that of the gorilla, but genetically the chimpanzee is closer to man than to the gorilla.
"In addition to that, the DNA sequence of an animal is much more accessible than the animal itself," says Graor. "There are molecular biologists who would not identify a whale even if it fell on them, but any biologist can put the whale's DNA on the computer screen and study it. The animal's features are recorded in its DNA, and a computerized analysis of the genetic material and proteins is enough for us to produce accurate and reliable information about the animal and the similarity that exists between it and other animals. Research of this kind allowed us to show a family relationship between the whale and ruminant animals, and specifically between it and the hippopotamus." The article linking the hippopotamus to the whale was published in 1997 in the journal Biology of Molecular Evolution. The distinct family relationship between the whale and the hippopotamus was finally confirmed in 1999 in an article by the Japanese researcher Norihiro Okada published in the journal Nature.
Computer analysis of DNA enables evolution researchers to deal with difficulties that apparently exist in Darwin's theory. An example of such a difficulty is explaining the development of complex traits in evolutionary terms. The lactating trait, for example, is a complex trait and in order to carry the trait the animal needs a lactating organ, a nutrient such as milk and a suckling reaction of the offspring. A complex feature is characterized by the fact that the reduction of one of its components eliminates the effectiveness of the feature. A breast without milk will not feed the child, and a baby without a sucking response will not enjoy the mother's milk.
It is particularly difficult to explain the development of a complex feature in organelles that are based on the coordinated activity of several proteins. The rod (tail) of bacteria, for example, is made up of dozens of proteins, and only their combined action allows the bacteria to move. So what was the role of these proteins before they learned to cooperate with each other?
These kinds of questions are raised by religious organizations and other bodies, which deny the theory of evolution and support the theory of creation. For them, the rod of the bacterium was created in its entirety.
Evolutionary researchers assume that if you remove one of the components of a complex trait, you are left with a less complex trait. "We assume that at an earlier stage in evolution the shoton proteins had a different role," says Prof. Graor. "In order to confirm the assumption, we scanned the genetic material of other bacteria and looked for an organ that is genetically similar to Shoton and that performs other functions."
Working together with Dr. Uri Gofna and Prof. Eliora Ron from Tel Aviv University, Graor was able to locate bacteria with shoton components, which do not aid in movement but are used by the bacteria to inject biological substances into the cells of the plant that houses it. The components of milk are not an invention of mammals either, and it is possible to find their relatives in the genetic material of bacteria.
"Our goal is to build animal family trees and reconstruct the history of molecular traits and entities such as the bat. Usually, work in the field does not have immediate practical significance, but a study like the one we conducted on Tay-Sachs disease definitely raises sharp questions about the way society is conducted."
Tay-Sachs is a genetic disease that causes the death of the baby in the first years of his life. The gene that causes Tay-Sachs has been identified, and it is especially common in Ashkenazi Jews. In order for a baby to develop the disease, he needs to receive two defective copies of the gene - one from the father and one from the mother. The father and mother are healthy because they carry a single copy of the defective gene, and only their pairing can lead to the birth of a sick baby. The only way to deal with the disease is preventively - there is a simple test that determines if a person is a carrier, and two carriers who have decided to get married can check if their fetus is sick, and if necessary perform an abortion.
Research students Ayala Arveli and Rotem Sorek developed a computer program that tests three behavioral models, which relate to the prevention of the disease. The models test the long-term results of different approaches to preventing Tay-Sachs; Each model inevitably leads to an increase or decrease in the prevalence of the defective gene in the population.
The first model simulates non-intervention in the prevention of the disease. The couple is not tested, the fetus is not tested and no abortion is performed anyway.
The second model advocates carrying out a carrier test for the couple, and the marriage of two carriers is conditional on them conducting genetic tests for the fetus during pregnancy. Identifying a sick fetus allows parents to perform an abortion. This approach is accepted by most secularists, even though it has a reproductive price - a certain number of pregnancies and fertile years go down the drain.
The third model is accepted mainly in ultra-Orthodox society, and is based exclusively on prevention in the stage before marriage. Every single man and woman undergoes a pregnancy test and marriage between a man and a woman who carry the disease is not possible. This approach reduces the number of sick babies, but it should be remembered that in a family where one of the parents is a Tay-Sachs carrier, there is a 50% probability that each of the children will inherit the defective gene.
"The results of the study show that the frequency of the defective gene increases in the population described in the third model," says Graor. "In the span of tens of generations, the prevalence of the gene in the ultra-Orthodox population will approach 350 percent, and men will have difficulty finding women worthy of marriage. In fact, within XNUMX generations, marriage between Ashkenazi ultra-Orthodox will not be possible in the State of Israel."
One response
Hahaha within 350 generations, I wish for the State of Israel to exist for 350 generations, unfortunately it seems as if another generation maximum two is all that is left.