USGS Paleontology glossary Acritarch microscopic organic structure from any of a number of organisms; common during the Proterozoic. Adaptive radiation, evolutionary radiation the rapid expansion and diversification of a group of organisms as they fill unoccupied ecological nichesevolving into new species. Age of Mammals term found in popular books on evolutionary systematics for the Cenozoic era, beginning with the Paleocene Epoch when following the K—T end Cretaceous mass extinctionmammals underwent a huge evolutionary radiation and thus replaced reptiles as the dominant life on Earth.
Thus, to achieve a modicum of breeding success, it is important that pigeon breeders understand the difference between - the reproductive potential and the external appearance of an individual bird. Genotype is the term used to describe the genetic makeup, as distinguished from the physical appearance, of an organism.
Some genes are hidden, and we cannot see them by looking at the physical appearance. The genotype determines the hereditary potentials and limitations of an individual. Among organisms that reproduce sexually, an individual's genotype comprises the entire complex of genes inherited from both parents.
Sexual reproduction guarantees that each individual has a unique genotype.
Phenotype, on the other hand, is the observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences as well as the interactions between the two.
You may have heard about the Human Genome Project. Unless you have an identical twin, you have a unique genome that determines all of your traits that can be seen, such as the color of your eyes.
Other traits cannot be seen, such as the exact chemical makeup of your eyeball. Phenotype is the expression the actual trait that we see of a specific trait, such as the ash-red or recessive red in pigeons.
A male pigeon, for example, can express itself as an ash-red bar in its phenotype.
Sex-linkage As you continue to study pigeon genetics, you will be hearing about sex-linked genes, because it is important to understand this concept in order to predict the breeding results of sex-linked genes.
Each human has two chromosomes that determine the sex and they are called X and Y chromosomes. In females, a dominant allele on one of the X sex chromosomes will mask a recessive allele on the other X. In males, a recessive allele on the X sex chromosome will show up because there is no matching allele on the Y.
In sex-linked inheritance, alleles on sex chromosomes are inherited in predictable patterns since males and females have different sets of chromosomes, XX and XY.
Typically the X chromosome is longer and it bears a lot of genes not found on the Y chromosome. Thus, most sex-linked genes are X-linked genes. Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual. Let us look at sex-linked inheritance in humans to understand this concept.
The following, inevitably incomplete, introductory glossary of terms and concepts links to other topics discussed elsewhere on this site, as well as including general topics of interest such as well-known prehistoric animals. - An organism would need to undergo the process of meiosis when it becomes mature enough to produce sperm (male) or eggs (female). In humans, following the stages of puberty the body becomes able to produce eggs and sperm through meiosis. Need a dependable person so I can address all my urbanagricultureinitiative.com the future I tip to word response explaining why the process of mitosis and meiosis are both important to a .
In humans, two well-known X-linked traits are hemophilia and red-green color blindness. Hemophilia is much more common in males than females because hemophilia is located only in the X chromosome.
Males are heterozygous XY - they only have one copy of the gene X in question - and therefore express the trait when they inherit one mutant allele. In contrast, a female must inherit two mutant XX alleles homozygous to have hemophilia, a less frequent event since the mutant allele is rare in the population.
Females with only one affected X chromosome will be carriers. Another example of sex-linked recessive inheritance is color blindness in humans. Color blindness is much more common in males than females because this mutation is also located on the X chromosome.
Males have no alternative copy of the X chromosome to correct this problem, but females have a second X, a safety backup that compensates. If a female human has one copy of this mutant gene, she will just be a carrier but will have normal color vision.
For females to have hemophilia or color blindness, they must inherit both affected X chromosomes from both of their parents. This reduces the chances of inheritance compared to male humans. The picture on the right demonstrates the mating of an unaffected father and a carrier mother.
If a male human is hemophiliac or color blind, he must have gotten this X gene from his mother, and if a female human is a carrier, she could have gotten the affected X gene from either of her parents. Thus, by definition hemophilia and color blindness are sex-linked recessive genes located on the X chromosome.
Pigeons have no external sex organs so it's often difficult to tell a male from a female. But if we know the pedigree ancestry of the father and the mother of the offspring, and if their phenotypic traits are sex-linked, we can tell the gender of the offspring by looking at its phenotype.An organism needs mitosis when the cells in the organism divide and grow.
Meiosis is needed for the sex cells in the organism for reproductive purposes. For example, eggs and sperms need meiosis. Meiosis increases the genetic variation which allows for evolution and the adaptation of .
The top problems with evolution explained using scientific evidence against evolution. In the creation evolution controversy, it is clear not only that the theory of evolution is wrong, the theory of evolution is false, but that the theory of evolution is a lie. Apr 10, · Best Answer: Mitosis creates identical genetic copies of cells.
This is how multicellular organisms grow larger and repair damage. Meiosis creates haploid gametes. These are the cells used in sexual reproduction (sperm in males and eggs in females).Status: Resolved. Aug 09, · Meiosis, on the other hand, is a process of taking a diploid cell (a cell with the full number of chromosomes) and producing haploid gametes (cells with only half the number of chromosomes).
Meiosis occurs to produce sperm and egg cells which then can combine to produce the diploid urbanagricultureinitiative.com: Resolved. Need a dependable person so I can address all my urbanagricultureinitiative.com the future I tip to word response explaining why the process of mitosis and meiosis are both important to a .
Meiosis (/ m aɪ ˈ oʊ s ɪ s / (); from Greek μείωσις, meiosis, which means lessening) is a specialized type of cell division that reduces the chromosome number by half, creating four haploid cells, each genetically distinct from the parent cell that gave rise to them. This process occurs in all sexually reproducing single-celled and multicellular eukaryotes, including animals, plants.