Need help on these questions. Thanks! How can a DNA microarray be used to determ

Question

Need help on these questions. Thanks!

How can a DNA microarray be used to determine if fetal DNA harbors mutations and/or chromosomal alterations?

How can allele specific probes be used to determine if someone is a carrier of a disease associated with recessive allele?

What is X-inactivation? How does X-inactivation result in the production of a calico cat? Most calico cats are female, why?

What is X-linked inheritance? Be able to utilize a punnett square to determine possible progeny outcomes if prospective parent genotypes are known.

What is the role of meiosis? What are homologous pairs versus pairs of sister chromatids?

How did Mendel’s experiments show gene segregation? What is gene (allele) segregation?

Explanation / Answer

DNA microarrays has attached to small DNA probes which hybridize to the DNA in sample and produce a signal that is detected. If there is a mutation in the gene then there wont be any hybridization and hence the signal wont be detected. The color of the signal corresponds to the affinity of the binding. The color spots on the screen correspond to the DNA probe on the microarray chip.

For a recessive disease to manifest, the patient has two posses two copies of the alleles. Two copies of the allele in a diseased person will give an increased signal due to increased hybridization than a sample with one allele which will be present in a carrier.

X-inactivation is the process that occurs in the female where females are homozygotes to compensate the expression of genes present on the X chromosome so that both male and female produce same amount of gene products of the genes present on the X chromosome. This is necessary because males have one X chromosome and females have 2 X chromosomes. if X-activation does not take place, the females will produce twice the product of X-based genes present in the males. X-inactivation is condensation of one of the X-chromosome so that it can not be expressed (heterochromatin). Which of the two X-chromosomes if inactivated is random, so in some cells let say X1 is inactivated whereas in others X2 is inactivated. In calico cats, the gene for color is located on the X chromosome for two different alleles, lets say one is black and the other is brown. In such cases during the X-inactivation, some cells would express black allele, som will produce brown color, producing patches and the phenotype, calico

X-linked inheritance is inheritance of the genes present on the X chromosomes.

Meiosis occurs in the diploid cells of the gamete to produce hapolid cells, when these haploid cells or gametes from two parents are fused they reproduce the diploid organism. Besides maintaining the ploidy level, meiosis is also responsible to induce variations in the generations by segregation of alleles, crossing over. Homologues pairs are chromosomes with two chromatids which are called sister chromatids.

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