what is pseudoautonomal genes..??? please reply fast
Answers
Answer:
The pseudoautosomal regions, PAR1, PAR2, are homologous sequences of nucleotides on the X and Y chromosomes. The pseudoautosomal regions get their name because any genes within them are inherited just like any autosomal genes.
Answer:
“Functional wasteland,” “Nonrecombining desert,” and “Gene-poor chromosome” are only some examples of the different definitions given to the Y chromosome in the last decade. In comparison to the other chromosomes, the Y is poor in genes, being more than 50% of its sequence composed of repeated elements. Moreover, the Y genes are in continuous decay probably due to the lack of recombination of this chromosome. But the human Y chromosome, at the same time, plays a central role in human biology. The presence or absence of this chromosome determines gonadal sex. Thus, mammalian embryos with a Y chromosome develop testes, while those without it develop ovaries (Polani [1]). What is responsible for the male phenotype is the testis-determining SRY gene (Sinclair [2]) which remains the most distinguishing characteristic of this chromosome. In addition to SRY, the presence of other genes with important functions has been reported, including a region associated to Turner estigmata, a gene related to the development of gonadoblastoma and, most important, genes related to germ cell development and maintenance and then, related with male fertility (Lahn and Page [3]). This paper reviews the structure and the biological functions of this peculiar chromosome.
STRUCTURE OF THE Y CHROMOSOME
The Y is one of the smallest chromosomes in the human genome (∼ 60 Mb) and represent around 2%–3% of a haploid genome. Cytogenetic observations based on chromosome-banding studies allowed different Y regions to be identified: the pseudoautosomal portion (divided into two regions: PAR1 and PAR2) and the euchromatic and heterochromatic regions.
The Pseudoautosomal regions (PAR): PAR1 is located at the terminal region of the short arm (Yp), and the PAR2 at the tip of the long arm (Yq). PAR1 and PAR2 cover approximately 2600 and 320 kb of DNA, respectively. The pseudoautosomal regions, and in particular PAR1, are where the Y chromosome pairs and exchanges genetic material with the pseudoautosomal region of the X chromosome during male meiosis. Consequently, genes located within the PAR are inherited in the same manner as autosomal genes. The euchromatic region is distal to the PAR1 and consists of the short arm paracentromeric region, the centromere and the long arm paracentromeric region. Finally, the heterochromatic region comprises distal Yq corresponding to Yq12. This region is assumed to be genetically inert and polymorphic in length in different male populations, since it is composed mainly of two highly repetitive sequences families, DYZ1 and DYZ2, containing about 5000 and 2000 copies of each respectively.
Whereas PAR1 and PAR2 represent the 5% of the entire chromosome, the majority of the length of the Y (95%) is made by the so-called “Non-Recombining Y” (NRY). This includes the euchromatic and heterochromatic regions of the chromosome. Whereas the heterochromatic region is considered genetically inert, the euchromatic region has numerous highly repeated sequences but also contains some genes responsible for important biological functions that we will review here.