The gene for red green color blindness is a recessive one designated X c Normal

The gene for red green color blindness is a recessive

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The gene for red-green color blindness is a recessive one designated X c . Normal color vision, designated X C , dominates. The C/c genes are located only on the X chromosome, so the ability to see colors depends entirely on the X chromosomes. The possible combinations are as follows: Only females who have two Xc genes are red–green color-blind. This rare situation can result only from the mating of a color-blind male and a color-blind or carrier female. Because males do not have a second X chromosome that could mask the trait, all males with an Xc gene will be red–green color-blind. The following figure illustrates the inheritance of red-green color blindness in the offspring of a normal male and a carrier female using both a Punnett square and a pedigree. Both a Punnett square and a pedigree for the sex-linked trait of colorblindness are shown. In sex-linked traits, the recessive trait affects males disproportionately, and they can easily skip a generation. Female carriers will pass the recessive trait to 50% of her sons, on average. Pedigree Analysis Decision Tree: As you can see, remembering three questions can help you distinguish among sex-linked versus autosomal dominance. Observing mixed traits in offspring indicate incomplete dominance, while observing both traits in a single individual indicates codominance.
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PCR AND GENETIC TESTING PCR Amplifies Selected DNA Sequences: PCR uses repeated cycles of temperature to amplify particular DNA segments. In the first step, the reaction mixture is heated to separate the DNA strands.
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The reaction is then cooled to allowed the DNA primers, which define the sequence to be amplified, to anneal (base pair) with the template DNA. In the third step, DNA polymerase extends the DNA primers to create a copy of the target DNA sequence. Heating the reaction to stop polymerization and separate the DNA strands starts the cycle over again. In each cycle, the two strands of the duplex DNA are separated by heating, then the reaction mixture is cooled to allow the primers to anneal (or pair) to their complementary segments on the DNA. Next, the DNA polymerase directs the synthesis of the complementary strands. The use of a heat-stable DNA polymerase eliminates the need to add fresh enzyme after each round of heating (heat inactivates most enzymes). In the presence of sufficient primers and dNTPs quantities, PCR is carried out simply by cycling through the different temperatures for strand separation, primer annealing, and DNA synthesis. Components Needed for PCR? Needed for replication? Function DNA Polymerase Yes Yes Synthesizes the new strand of DNA Thermocycler Yes No Machine that cycles through the different temperatures needed for PCR DNA Ligase No Yes Ligates Okazaki fragments RNA Primer No Yes Initiates DNA replication dNTPs Yes Yes Building blocks of DNA, needed for DNA synthesis DNA Primer Yes No Initiates DNA synthesis in PCR
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