Y chromosome, the smallest chromosome of the karyotpe, is one of the two sex chromosomes. In 1905, Nettie Stevens identified that Y chromosome is a sex-determining chromosome, while conducting one study of the mealworm Tenebrio molitor. He also proposed that chromosomes always existed in pairs. In 1890 Hermann Henking discovered that Y chromosome was the pair of the X chromosome. All chromosomes normally appear to take on a well defined shape during mitosis when seen under microscope. This shape is vaguely X-shaped for all chromosomes. Interestingly, the Y chromosome looks like the English alphabet Y during mitosis, due to merging of the two very short branches (Bainbridge, 2003). Every species organism consists of different set of chromosome with one set of sex determining chromosome.
The X and Y chromosomes are thought to have evolved from a pair of identical chromosomes, known as autosome. The mammalian males are heterogametic (produces X and Y chromosome bearing sperms in equal proportions), and the females are heterogametic (all female gametes are X bearing). It was found that Y chromosome has high repetitive DNA sequence content which consists of pseudogenes and does not have any function (Delbridge et al., 1999). In males, Y chromosome consists of SRY gene which triggers embryo development as male. Y chromosome is the smallest chromosome consists of 2-3% of haploid genome and contains between 70 and 200 genes (Quintana-Murci et al., 2001). Y chromosome consists of 2 arms- short arm (Yp) and long arm (Yq). These arms consist of 2 pseudoautosomal regions PAR1 and PAR2 which recombine with their homologous regions on X chromosome. The absence of recombination makes genetic mapping of the Y-specific region impossible, and the ...
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...requency in Human Y Chromosomal UTY Gene. OMICS A Journal of Integrative Biology Volume 15, Number 3, 2011
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C. elegans males are produced rarely in a hermaphrodite population by meiotic non-disjunction at a frequency of 0.1%. Non-disjunction is, according to the Genetics Home Reference, when chromosomes or chromatids fail to separate properly. (Genetics Home Reference) . Males have only one X chromosome. This is supported in the Developmental Biology Journal when it is stated that the hermaphrodites are XX and the males are XO (Morgan, Critte...
Meiosis, also called reduction division, is a distinct type of cell division that is essential for sexual reproduction to occur. It is one in which two successive divisions of diploid cell occur thereby producing four genetically different haploid daughter cells, also called gametes, each with half the number of chromosomes and thus, half the total amount of genetic material as compared to the amount before meiosis began. Interphase precedes meiosis and thus, paves the way for meiosis to eventuate as the cell’s DNA replicates in the S phase yielding corresponding, identical chromosomes. Interphase sparks the marvelous process of meiosis that allows variation to transpire within the organisms it occurs, hence, giving rise to millions of organisms with unique aspects unlike any other on Earth. Because meiosis is a form of sexual reproduction itself, it is the means through which gametes are produced, each with a reduced number of chromosomes, so that when two gametes fuse during fertilization, not only do they form a diploid zygote with 46 chromosomes, but also have manifested differing features due to the rearrangement (crossing-over) of chromosomes.
Turner’s syndrome is a genetic conditions that affects the female’s sex chromosome. In (http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001417/) Turner’s syndrome occurs when cells are missing all or part of an X chromosome. It’s common of the female patient to only have one X chromosome. Although, some individuals may have two X chromosomes but one is defective. It is thought that an estimated 1 out of 2000-2500 females suffer from this genetic condition worldwide but it’s usually females with this condition don’t survive their birth. Due to this abnormality, the genes that is defective “affect the growth and sexual development of the female” (http://learn.genetics.utah.edu/content/disorders/whataregd/turner/). However other disabilities and delays do occur even though these traits can vary case by case.
Both of these methods can help determine and eliminate genetic disorders, as certain conditions can be screened out using these technologies. As discussed in Meseguer et al., more than 300 diseases have been related to sexual chromosomes till date. Case studies also argue the important role of these methods in family balancing for varied family dynamics who aim to compensate their family with a representation of the other sex (Meseguer et al., 2002). Critics have also mentioned that with an increase in demand, these methods could become more economical and widely available, including to couples who may need it due to medical
Jacob Syndrome is a rare condition where males contain an additional copy of the Y chromosome in their cells. According to the Genetic and Rare Diseases Information Center, (GARD, 2012), other names for Jacob Syndrome include: 47, XYY syndrome, XYY Karyotype, and YY syndrome. Statistics from Genetics Home Reference (2014) state that Jacob Syndrome appears in approximately 1 in 1,000 male newborns. In the United States, 5 to 10 male newborns have Jacob Syndrome.
Mannaert A A PCR survey for posterior Hox genes in amphibians. Mol Phylogenet Evol. 2006 Feb;38(2):449-58. Epub 2005 Sep 28.
In order to test the hypothesis and ensure that other genes in the larger chromosome region were not the real cause of pelvic loss the scientists generated F1 hybrids between both pelvic-completed and pelvic-reduced sticklebacks as well as two pelvic-complete populations. These F1 hybrids allowed for combination of the alleles of Pitx1 from pelvic-complete (FRIL, LITC) and pelvic-reduced (PAXB) populations. Brain and pelvic tissues were isolated to compare the expression of either the LITC or PAXB allele to the FRIL allele. The results supported the initial hypothesis as expression of the PAXB Pitx1 allele was greatly reduced in the pelvis but not the head of F1 hybrids, indicating a tissue-specific, cis-regulatory change in the Pitx1 locus. If indeed other genes in the larger chromosome region were the real cause of pelvic reduction then there would have been a secondary or trans-acting reduction seen in the expressions of Pitx1 in both
Gender is determined by the sex chromosomes, XX produces a female, and XY produces a male. Males are produced by the action of the SRY gene on the Y chromosome, which contains the code necessary to cause the indifferent gonads to develop as testes (1). In turn the testes secrete two kinds of hormones, the anti-Mullerian hormone and testosterone, which instruct the body to develop in a masculine fashion (1). The presence of androgens during the development of the embryo results in a male while their absence results by default in a female. Hence the dictum "Nature's impulse is to create a female" (1). The genetic sex (whether the individual is XX or XY) determines the gonadal sex (whether there are ovaries or testis), which through hormonal secretions determines the phenotypic sex. Sexual differentiation is not drive...
In this experiment, Mendelain Models are observed. The purpose of the experiment is to understand how traits are passed from one generation to the other as well as understanding the difference between sex linked and autosomal genes. One particular trait that is observed in this experiment is when a fly is lacking wings, also known as an apterous mutation. In this experiment, we will determine whether this mutation is carried on an autosomal chromosome or on a sex chromosome. The data for this experiment will be determined statistically with the aid of a chi-square. If the trait is autosomal, then it will be able to be passed to the next generation on an autosomal chromosome, meaning that there should be an equal amount of male and
These two blood samples that we observed were the karyotypes of a female human and a female horse. What is significant about this experiment is the fact that neither sample A3 or B23 suffer from any form of variance. We can confirm that the human karyotype is healthy, supported by Pathology (2015), and the horse karyotypes are also healthy, with evidence from Horseman (2015). From the images provided we can see there is no significantly apparent mutation or missing chromosomes. As a karyotype test provides information about the number of chromosomes a person has, the structure of their chromosomes and the sex of the individual, it is able to distinguish if said person will suffer from any sort of disorder, such as Down syndrome. Down syndrome is a congenital condition caused by an extra chromosome. “For example, if a human karyotype depicts that a patient has three copies of the 21st chromosome, instead of two, the patient is diagnosed with Trisomy 21, also known as Down's syndrome”. (Innovateus.net, 2015) This is one significant way that karyotyping is used in the modern
Thomas Hunt Morgan, Calvin Bridges and their colleagues have been recognized for their work in discovering recombination frequencies, the chance of a crossover occurring between sister chromatids, and identifying and mapping the location of genes for each chromosome. Their work began in the
National Institute of General Medical Sciences. (2010). "21st-Century Genetics." The New Genetics, p. 74-83. Retrieved from http://publications.nigms.nih.gov/thenewgenetics/chapter5.html
DNA is the fundamental unit of heredity. Chromosomal Euchromatin, heterochromatin together with telomere enable cell division associated genetic recombination of paternal and maternal chromosomes at the time meiosis by crossing over of sister chromatids with chaisma. This DNA contains heritable
During prophase I, homologous chromosomes pair and form snynapses. The paired chromosomes are called bivalents, and the formation of chiasmata caused by genetic recombination becomes apparent. The bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent.
The X-chromosome is one of the two sex chromosomes(the other being Y) that is responsible for a variety of factors in a child’s developmental growth, the most commonly known being their biological sex. Researchers at the National Center for Biotechnology Information have studied the X-chromosome and its relation to homosexuality in men. Preceding their studies, the researchers hypothesized, “If the X Chromosome contains a gene that increases the probability of an individual’s being homosexual, then genetically related gay men should share X chromosome markers close to that gene. If no such gene exists, then no statistically significant correlations between sexual orientation and X chromosome will be observed” (Bocklandt, Horvath, Vilain, Hamer).