Who discovered sex linked traits. human genetic disease 2022-12-24
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The discovery of sex-linked traits can be traced back to the early 20th century, with several key figures contributing to our understanding of this concept.
One of the earliest scientists to study sex-linked traits was Thomas Hunt Morgan, an American geneticist and zoologist. Morgan made several key discoveries in the field of genetics, including the concept of the gene and the role of chromosomes in heredity. In the 1910s and 1920s, Morgan and his team conducted experiments on the fruit fly Drosophila melanogaster, which has a small genome and a short generation time, making it a useful model organism for genetic research.
Through his experiments, Morgan discovered that certain traits, such as eye color and wing size, were linked to specific chromosomes. He also found that these traits could be inherited in a predictable pattern, with some traits being more common in one sex than the other. These discoveries helped establish the concept of sex-linked inheritance, in which traits are determined by genes on the X or Y chromosomes.
Another important figure in the study of sex-linked traits was Alfred Henry Sturtevant, a student and colleague of Morgan's. Sturtevant developed the first genetic map, which showed the relative positions of genes on a chromosome. This allowed scientists to more accurately predict the inheritance patterns of sex-linked traits, as they could see which genes were located near each other on the chromosome.
In the following decades, other scientists such as Calvin Bridges and Theophilus Painter further expanded our understanding of sex-linked traits and their role in genetics. Through their research and the work of many others, we now have a much clearer picture of how sex-linked traits are inherited and how they can be used to study genetic disorders and other medical conditions.
Overall, the discovery of sex-linked traits has had a significant impact on the field of genetics and has helped us understand the complex mechanisms behind heredity. The contributions of Thomas Hunt Morgan, Alfred Henry Sturtevant, and others have laid the foundation for much of the genetic research that is conducted today.
Sex Linkage
With evidence drawn from cytology he was able to refine Mendelian laws and combine them with the theory—first suggested by Theodor Boveri and Walter Sutton—that the chromosomes carry hereditary information. The members of the resulting F 1 generation had all red eyes, but Morgan suspected that the white-eye trait was still present yet unexpressed in this hybrid generation, like a recessive trait would be. Although a full appreciation of the extent to which medically important disease genes are conserved between humans and Drosophila was not possible until the sequencing of the fly genome Reiter et al. Morgan never looked back, and he developed a huge following of accomplished students over the next few decades. Through more breeding analysis, Morgan found that the genetic factor controlling eye color in the flies was on the same chromosome that determined sex. In some groups of organisms with sex chromosomes, the sex with the non-homologous sex chromosomes is the female rather than the male.
Thomas Hunt Morgan and the Discovery of Sex Linkage
Morgan was sure that Wilson and the other researchers who promoted the chromosome theory of inheritance were looking for an easy answer as to how independent assortment occurred in gamete formation, because he believed they ignored counterevidence in the face of excited conviction. Chromosomal sex determination, where one gene commonly acts as the primary sex determination cue, is prevalent. There are two basic genetic mechanisms by which sexually dimorphic phenotypes can be produced from a shared genome: sex linkage on sex chromosomes, and sex-limited expression of autosomal loci. Table 4: Morgan's Second Test Cross Male Gametes X + Y Female Gametes X + X + X + X + Y X w X + X w X w Y As shown in the table, the offspring of this cross exhibited a 3:1 ratio of red eyes to white eyes, which indicated that white eyes were recessive. Morgan's early days of scientific training had taught him that, in order to find an answer, he must design an experiment that asked the right question.
Sex Linked Inheritance: Characteristics, Types and Disorders
He worked on a male bug and noticed that only 50% of the sperm received the nuclear structure and named it as X- body. Thus, second-generation offspring would include one-quarter with white eyes—and all of these would be male. Later on, by a further investigation by some scientists, it was found that this X- the body is a chromosome, so it was renamed to X- chromosome. Surprisingly, all white-eyed flies were male. In general, it can be said that risks of recurrence are not as great for multifactorial conditions as for single-gene diseases and that the risks vary with the number of relatives affected and the closeness of their relationship. When the sex chromosomes are heteromorphic, large size differences are apparent through staining of chromosomes. Cox, in Encyclopedia of Animal Behavior, 2010 Proximate Mechanisms Studies that attempt to address the factors driving the evolution of sexual dimorphism are often referred to as studies of ultimate causation.
One indication of this is the fact that male ducks in dichromatic species, as juveniles, display female plumage and only later, as adults, develop male sexual dichromatism Omland, 1997. Fish that consistently yield 1:1 sex ratios are likely to have chromosomal sex determination; those that deviate from 1:1 sex ratios probably have polygenic or environmental sex determination. Morgan's early days of scientific training had taught him that, in order to find an answer, he must design an experiment that asked the right question. When a trait or character is co-inherited with the Y chromosome, it segregates from fathers to sons. Now, consider a cross between a homozygous white-eyed female and a male with red eyes. In addition to cytogenetic techniques or in cases where no visible differences can be detected by the above techniques, analysis of sex-linked traits or genetic experiments have revealed the sex determination mechanisms of many fish see below.
Therefore, Morgan correctly proposed that the strength of linkage between two genes depends upon the distance between the genes on the chromosome. Therefore, it is essential to experimentally determine if the trait is sex specific as a result of coinheritance with the sex determination locus or due to the sex-specific hormone regulation. Using androgenesis and gynogenesis to determine the sex chromosome system. Thus, he first performed a test cross between the white-eyed male fly and several purebred, red-eyed females to see whether white eyes might also occur in the next generation. To test these predictions, Morgan crossed a white-eyed female with a red-eyed male, as depicted in Table 6.
He worked on a male bug and noticed that only 50% of the sperm received the nuclear structure and named it as X- body. It is difficult to distinguish these two mechanisms in the absence of genetically informative data, as both may lead to a similar level of sexual divergence in prevalence. Fish are treated with hormones prior to sex differentiation. In Oryzias Luzonensis, a close relative of the Japanes medaka O. The disease gene associated with Upon rare occasion, persons are identified with an imprinted gene disorder who show no family history and do not appear to carry any mutation in the expected gene.
In particular, Morgan began to entertain the possibility that association of eye color and sex in fruit flies had a physical and mechanistic basis in the chromosomes. The discovery of these sex determination genes in diverse fish species, uncovers some common and unique aspects with regards to genetic sex determination in fish. The trait is determined by both the nuclear genetic system a single gene with right-handed allele dominant to left-handed allele and the maternal nuclear influence. With respect to Drosophila eye color, when the P male expresses the white-eye phenotype and the female is homozygously red-eyed, all members of the F1 generation exhibit red eyes Figure 16. The colourful vision of the eye is due to the cone cells present in the retina of the eye.
The X- chromosome has no counterpart in males, so the genes present, either in dominant or recessive form, are always expressed in males. Using this method, sex-specific loci or repetitive elements mark the sex chromosomes. These cases are now known to result from Diseases caused by multifactorial inheritance Genetic disorders that are multifactorial in origin represent probably the single largest class of The table lists some conditions associated with multifactorial inheritance. Successive matings of individual pairs of fish can reveal whether or not sex is genetically determined. One day in 1910, American geneticist Thomas Hunt Morgan peered through a hand lens at a male fruit fly, and he noticed it didn't look right. Both groups of disorders exhibit a distinctive pattern of non-Mendelian inheritance termed anticipation, in which, following the initial appearance of the disorder in a given family, subsequent generations tend to show both increasing frequency and increasing severity of the disorder. When a female parent is homozygous for a recessive X-linked trait, she will pass the trait on to 100 percent of her male offspring, because the males will receive the Y chromosome from the male parent.
Crossing of the resulting fish to natural males or females can confirm the sex chromosome contents through production of predictable sex ratios, shown outside of the shaded boxes. Boycott crossed the two types of L. Again, predictable sex ratios arise depending on the chromosomal mechanism of sex determination Figure 2. Furthermore, sex-limitation occurs if different sets of genes are operating between the sexes. This is a clear indication that multiple genetic factors determine sex.
It shows that the recessive allele is expressed in male-only. The 23rd pair of chromosomes is called the sex chromosomes and is indicated by the letter x for females and the letter y for males. Because the genetic and environmental factors that underlie multifactorial disorders are often unknown, the risks of recurrence are usually arrived at empirically. In addition to the theoretical arguments to be presented in sections of the basic allopatric model and the peripatric model in Chapter 18, that explanation is discredited by the fact that while yellow-green color is lost in the plumage, it is conserved in the bill of many monochromatic birds Omland, 1997 , suggesting that the loss of the plumage color is not related to changes in sex chromosome-linked genes or any other gene. These results were suggestive for hypotheses of which Morgan himself was skeptical. If the father is affected, the son will always be unaffected, but the daughter will always be affected.
