Dominant and recessive phenotypes. (1) Parental generation. (2) F1 generation. (3) F2 generation. Dominant (red) and recessive (white) phenotype look alike in the F1 (first) generation and show a 3:1 ratio in the F2 (second) generation Originally from en:Nupedia, by Benutzer:Magnus Manske (Photo credit: Wikipedia)
The findings described in Evolution Blogspot 18 make it no longer tenable to presume that the myriad different forms of organisms currently extant or those that preceded modern organisms came by specific and different mutation-produced adaptations, separate and distinct from each other. It is highly improbable that such directed diversity could have happened over any amount of time. A more simple, rapid, and efficient basis for evolution has been delineated. This evolutionary efficiency is based on Hox “tool-kit” transcription factors that turn tool-kit genes on and off, signaling cell groups that communicate with other crucial clusters of amino acids, and “switch” genes, and the changes they undergo. Perhaps the most dramatic aspect of these findings is the common ancestry of such diverse creatures as worms, fish, flies, and humans. The finding of the genetic basis of heredity and evolution has now been convincingly linked to the abundant fossil record; the present is a key to the past.
Developmental regulatory genes–also called master control genes–constitute a small fraction of the genome, and encode transcription factors or signaling proteins, that directly–through direct DNA binding–or indirectly–through signal transduction cascades–regulate the expression of other genes and control key aspects of development and formation of specific body parts. (Sean B. Carroll, et.al, From DNA to Diversity. Molecular Genetics and the Evolution of Animal Design. Blackwell Science, 2001).
This very brief elucidation of Evolutionary Development leads to an understanding of the mechanisms of evolution which will be equally briefly described in this blogpost. Beginning with the ancient Greeks and on through the Jews, early Christians, and Muslims until the twentieth century, most people, even educated ones saw human reproduction, and indeed, all animal reproduction as the implanting of a seed passed from the male into the female as passive receptacle. The concept of heredity was on the level of a “mixing of bloods”.
The scientific understanding of heredity and thence to the
Other rules related to the fact that not all alleles are strictly dominant or recessive, although the characteristics Mendel studied were. The more complex hereditary principles related to differing degrees of dominance came from later researchers and included such elements as: incomplete dominance, co-dominance, polygenic inheritance, epistasis, and pleiotropy, which are less basic to the understanding of evolution and will not be further described here. In the next blogspot, a discussion of genes, gene expression, and DNA will be presented along with the tie of that area of molecular biology/genetics to the process of evolution. continued…understanding of evolution began in the nineteenth century. Austrian monk Gregor Mendel (1822-1884) in experiments with pea plants discovered the underlying principles of inheritance. Using the pea plant, Pisum salivum, which had a short generation time, many offspring, was small and easy to grow, had many varieties, and had eggs that could be manually fertilized with sperm thereby guaranteeing known parentage, he derived laws of inheritance that hold today. Mendel postulated rules of inheritance based on his hypothesis, his scientific experimentation, and finally on his validated theory. His rules produced and understanding of what was happening in heredity: 1. The units that determine characteristics, or traits, come in more than one form or allele. 2. Each gamete–a sperm or egg cell–contains one copy of a particular gene. When gametes fuse during fertilization, the resulting offspring contain two copies of each gene–the principle of segregation–which states that pairs of genes separate during meiosis and form new pairings as gametes fuse during fertilization. 3. Each organism possesses two alleles for each gene, one from each parent. An organism is said to be homozygous for a specific trait if it inherits two identical alleles for the corresponding gene. An organism is heterozygous if the two genes are different. 4. In a heterozygous organism, one trait may be fully expressed, or dominant, while the opposing trait is not expressed at all, or recessive. Recessive alleles are only expressed if the organism is homozygous for that gene. 5. The alleles of different genes are assorted randomly and are independent of each other–this rule of independent assortment.