Which among the following is wrong about test cross
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Displaying 961 - 965 of 1057 questions. Show Please, kindly accept my apology for repeating my query. How is the formula "1q42.2" read? Is it read as: Asked by: Ahmed Shoukry Amin Latest Reply: Hello Ahmed. Your version 2 is the closest. Specifically, you can read it like this: “sub-band 2 of band 2 of region 4 of the long arm of chromosome 1.” If you would like to see an example of how scientists report their findings with this genetic position terminology, you may find this short article helpful. The article is about how specific genetic deletions can cause visceral organs to grow in the wrong position inside the abdominal cavity. http://www.ncbi.nlm.nih.gov/pubmed/10360400?ordinalpos=4&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum Reply From: Rachel Davis Apr 22, 2009 02:43PM How do scientists decisively know whether a trait is dominant or recessive? Asked by: Ahmed Shoukry Amin Latest Reply: Scientists usually determine whether a trait is dominant or recessive by doing a test cross. Test crosses involve breeding the individual in question with another individual that expresses a recessive version of the same trait. If all offspring display the dominant phenotype, the individual in question is homozygous dominant; if the offspring display both dominant and recessive phenotypes, then the individual is heterozygous. Reply From: Daniel Martin Apr 21, 2009 07:57PM I was wondering what a minor allele was? I thought it might be recessive but I'm sure that is the case. Thank you Asked by: Emma Cussans
Latest Reply: Hello Emma. No, it doesn’t have anything to do with being recessive. The term “minor allele” refers to how often the allele occurs within a given population, otherwise known as its frequency. You see minor and major alleles at a given position in the genetic code, or locus, when there's more than one option for a given position. Like switching the letters in the word "grey" to get "gray" -- a tiny change that doesn't change the meaning of the word. In DNA, these small changes in one nucleotide (A, T, C, or G) are called single nucleotide polymorphisms (SNPs). What's important is that even though SNPs don't always change the meaning of the genetic code, they can be used to tell how closely one string of DNA is related to another. For example, if someone uses the word "grey," you could bet that they were from Britain. If someone uses the word "gray," he or she is probably from the United States. Anyway, back to SNPs. When a single nucleotide differs between members of a species, or between paired chromosomes in an individual, these differences are called SNPs. So, if one allele is less frequent than all others, it is called the minor allele. Whichever SNP is less frequent in a particular population can be called the minor allele, so the frequency of this allele is called the "minor allele frequency." For more on the broad applications of SNPs in genetic research, check out the following resources on Scitable: http://www.nature.com/scitable/content/SNP-4815 http://www.nature.com/scitable/topicpage/Using-SNP-Data-to-Examine-Human-Phenotypic-706 Reply From: Rachel Davis Apr 21, 2009 12:07PM Is it possible to have a negative heritability for a trait? Asked by: Gloria Obianugba
Latest Reply: Hello Gloria. No, heritability cannot be negative. Heritability is actually a ratio of positive numbers called variance components, so the number is always positive. Therefore, the value of heritability always lies between 0 and 1. For example, the calculated heritability for human height is ~0.8. For traits associated with fitness in animal populations, heritability is usually 0.1-0.2. Basically, the fact that heritability is calculated as a ratio of two positive numbers means it can never be negative. For a more detailed discussion of the mathematics of trait heritability, check out: http://www.nature.com/scitable/topicpage/Estimating-Trait-Heritability-46889 Reply From: Rachel Davis Apr 21, 2009 12:06PM Polydactyly is a human monogenic trait. Knowing that it is caused by a dominant gene and the affected person is actually homo-or heterozygous makes me feel troubled when trying to explain it to 1st year genetics students!!!!!!!!!!???. I know that dominance does not mean commonness. But I wonder if the gene product of the dominant allele prevents the expressability of the recessive allele so the phenotype of polydactyly shows up. I might be wrong in this postulation, but the relation between dominant and recessive phenotype is still obscure concerning the struggle for their prevalence. Please, help me "in simple words" to explain how polydactyly is a dominant trait? Asked by: Ahmed Shoukry Amin Latest Reply: Hello Ahmed. It can be confusing to understand why a dominant allele isn’t always the most common allele. The truth is, the alleles responsible for polydactyly can occur in many genes that direct embryonic development. When an allele causes such a gene product to be overexpressed, or expressed at the wrong time during development, a child is born with six fingers. Whether an allele is common or rare in a population does not depend on whether the allele is dominant or recessive. Dominance occurs when one allele masks the phenotype of another allele. In the case of polydactyly, an allele can become rare when the resulting phenotype is not an advantage for the organism. In extreme cases, alleles become rare when the homozygous genotype (two copies of the same allele) produces a lethal condition, before the organism reproduces. In the case of polydactyly, two dominant alleles prevent proper embryonic development and cause major embryonic defects that result in miscarriage.(1) One dominant allele is not lethal and only causes extra fingers or toes. Sometimes this doesn’t limit function – as in the case of Greg Harris, a pitcher with six fingers who played for the Montreal Expos. His six-fingered glove is now in the Hall of Fame! Here is a relevant image from Scitable: http://www.nature.com/scitable/content/Human-polydactyly-45676. 1 Biology: Life on Earth (7th ed.) by Audesirk, Audesird, and Byers. Reply From: Rachel Davis Apr 21, 2009 12:06PM
Send MessageWhich is correct about test cross?So, the correct optio is 'Each test cross is a back cross'.
What is test cross answer the following?Test-cross is an experiment in which an organism showing dominance for a specific trait has to be tested for its genotype. When an organism shows a dominant character, it could be homozygous or heterozygous for that character. Using the homozyous recessive organism, the genotype of the organism can be tested.
Which of the following statements best describe a test cross?The correct answer is (a) One individual has the dominant phenotype and the other has the recessive phenotype. A testcross is an experiment performed to determine whether the genotype of an organism with a dominant phenotype is homozygous or heterozygous.
What a test cross is used for?To identify whether an organism exhibiting a dominant trait is homozygous or heterozygous for a specific allele, a scientist can perform a test cross. The organism in question is crossed with an organism that is homozygous for the recessive trait, and the offspring of the test cross are examined.
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