Genes are the building blocks of heredity. They are passed from parent to child. They hold DNA, the instructions for making proteins. Proteins do most of the work in cells. Sometimes there is a mutation, a change in a gene or genes. The mutation changes the gene's instructions for making a protein, so the protein does not work properly or is missing entirely. This can cause a medical condition called a genetic disorder. Polydactyly or " many fingered", is a genetic disorder in which humans and animals have an abnormal amount of fingers and toes. In humans and animals, this condition can be present in one or both hands and feet. The extra digit is usually a small piece of soft tissue that can be removed. Occasionally it contains bone without joints; rarely it may be a complete functioning digit. The extra digit is most common on the ulnar (little finger) side of the hand, less common on the radial (thumb) side, and very rarely within the middle three digits. These are respectively known as postaxial (little finger), preaxial (thumb), and central (ring, middle, index …show more content…
A multiple birth is the culmination of one multiple pregnancy, wherein the mother delivers two or more offspring. A term most applicable to placental species, multiple births occur in most kinds of mammals, with varying frequencies. Each single fertilized egg (zygote) may produce a single embryo, or it may split into two or more embryos, each carrying the same genetic material. Quadruplets are much rarer than twins or triplets. As of 2007, there were approximately 3500 sets recorded worldwide. Quadruplet births are becoming increasingly common due to fertility treatments. There are around 70 sets of all-identical quadruplets worldwide. Many sets of quadruplets contain a mixture of identical and fraternal siblings, such as three identical and one fraternal, two identical and two fraternal, or two pairs of
Twins are truly fascinating from the time of separation of the embryo to birth; and still the complexity of twinning is not yet fully understood among the scientific world. Scientists have studied the human body from the time of prenatal development to birth, and still are in awe of the formation of twins. Research in twinning is ever more increasing in this field, leadi...
During ovulation, when a woman releases an ovum, three different processes can occur. First, the ovum can remain in one piece all the way to the uterus where, if not fertilized, it will be shed out of the body along with the unused endometrium. Second, the ovum, if fertilized, can develop into a single embryo, which is the most common type of pregnancy in humans with about 99% of all births being singletons (1). Finally, the ovum can split into two separate halves resulting in genetically identical twins. The three types of twins previously mentioned are identical, which are created when the fertilized ovum separates into two complete, identical parts, conjoined, which occur as a result of a fertilized ovum not completing the equal separation resulting in two fetuses fused together in some way, and half-twins or polar body twins, which are made when an unfertilized ovum splits into two complete, identical parts and is then fertilized by two different sperm. The frequency of identical twins is 3.5 per 100 births (1) and the frequency of conjoined twins is 1 birth per 50,000 with only 100 known cases surviving their first year (5).
Conjoined twins have one major cause, which makes them conjoined. When an egg is produced and is fertilized by sperm, 3 things can happen, the egg can grow and form only one fetus, the egg can split and form identical twins (triplets) or the egg can partially split and grow into conjoined twins. Usually identical twins are formed during the first 12 days after the conception date, but when the process happens the 13th or 14th day, the egg doesn’t fully se...
Twenty years ago, twin births were radically lower, with twins being more frequent than other multiple births. With technology becoming more advanced and people who normally have problems becoming pregnant can use in vitro fertilization, people delaying motherhood, and survival rate increasing; having twin children is not as rare as it was thought to be in the past. Twin birth rates have increased 42% from 1980 to 1994 (Lytton, Singh, & Gallagher, 1995).
Many couples who are infertile can not handle the financial responsibility of multiple children. If a couple has seven children in one pregnancy, the financial strain can lead to chaos. There were only three sets of living septuplets in the United States in 1997, according to the Knight-Ridder's journalist Tracy A.
Polydactyly is the most commonly observed congenital digital anomaly of the hands and feet appearing in 1 in every 500 live births. The condition is characterized by an abnormal amount of digits per hand in which the extra digits may develop bilaterally, or it may occur on both or just one hand, foot, or some other combination. Usually the extra digits that develop are either small pieces of soft tissue or fully formed in appearance. It is noted that in around 80% to 90% of cases involve the peripheral digits, although it is possible that all digits may be affected. Depending on the location of the extra digit, polydactyly can be further classified into three types: pre-, post-, and central axial forms. Polydactyly can occur as an isolated disorder (non-syndromic) or alongside other symptoms or disease. Isolated polydactyly is typically caused by the inheritance of an autosomal dominant gene mutation, meaning the cause is not due to a multifactorial trait. However, most cases of polydactylism are linked to specific syndromes that cause congenital anomalies through a variety of gene mutations.
... structure of many chromosomes ( chromosomal mutations). Mutations are not always bad because they can cause adaptation and variation in people.
Fraternal twins are the most common type of twins. They are the result of the union of two eggs and two sperm. Fraternal twins can be the same or different sexes (Wade 53). Segal says that, “They are two individuals, no more genetically alike than brothers and sisters that develop from separate fertilizations” (Segal 1). Amazingly, fraternal twins can be conceived at separate times and have different fathers. It seems to be a hereditable trait to conceive fraternal twins. Yet, tendency to conceive conjoined twins may be caused by genetic and environmental conditions (Hunter 1).
Before we start discussing how genetic tests are developed, let us discuss how genes can trigger disease. A sound body requires the action of many proteins working together. For a protein to function properly, an intact gene must encode for that specific protein. A mutation describes a gene which has been changed. The most common type of mutation is a single change of a nucleotide of DNA. Other types of mutations include the loss or gain of a nucleotide and the disappearance or multiplication of long segments of DNA. Mutations can have three effects: beneficial, harmful, or neutral. Mutations are beneficial if the fitness of an individual is enhanced. Harmful mutations can either slightly alter a protein, where the protein may still minimally function, or they may totally disable a protein. In this instance, the outcome is not only based on how a mutation alters a protein’s function, but on how important the protein is to the body (Understanding Gene Testing).
“A gene is a segment of DNA or a sequence of nucleotides in DNA that code for a functional product,” Tortora. Microbiology. p. 575. The syllable of the syllable. These genes not only affect our outlook, but also play a role.
a single egg or the fertilization of two eggs. In the case of dizygotic twins,
I have always been fascinated by conjoined twins and have always had questions about them like; what do the Siamese have to do with conjoined twins? Why does this form of twin happen? What, if any genes cause this? What types of Conjoined twins are there? How does the environment affect, if at all, the biological families' gene pool? In my research in efforts to prepare this paper, I found the answers to this question and many more. This term paper will cover the types of conjoined twins, the biological occurrence that causes conjoined twins, a look into some of the genetic and environmental causes of conjoined twins, the types of conjoined twins and the genetic and social impact of conjoined twins.
It is possible for pregnant women to lose one twin in a miscarriage but still carry the second child to full term without any damage resulting to it. This has happened rather frequently. “Whether all these twins born far apart were identical or fraternal is not known. However, these twins are all “ordinary” in the sense that they were carried in one womb” (Gaddis, Vincent & Margaret, 1972 (pp. 35-36).
Genetics is the passing of characteristics from parents to offspring through genes. Genes are information
Those who have arrived at the ovum try to drill through its shell. Those sperm cells that were able to drill through the shell are now in a space that is filled with liquid. If a sperm manages to penetrate into the cytoplasm of the cell nucleus, the fertilization takes place: Both the egg cell and the sperm cell have all stored the genetic information necessary for the development of a human being. Both fuse together during fertilization. Essential characteristics of the developing human being (gender, hair color, blood type, etc.) are therefore already defined from this point in time. Fusing of two sperm with just one egg is extremely unlikely. Immediately after fertilization by the first sperm cell, the outer layer of the “egg” becomes impassable for more sperm. Should it nevertheless occur, then the double-fertilized egg in these cases is not viable and will not usually grow. The child (so to say) is not able to correctly develop and severe disabilities can form, in most of these cases the body will discard the fertilized egg at some point. If the child is carried to full term they will most likely be triploid, and have an extra set of chromosomes in their cells. Triploidy is considered a lethal