State the conclusions reached by Mendel on the inheritance of characteristics.How do the following deviate from his conclusions?
2.sex-linked (X-linked) inheritance.
3.polygenic (multiple-gene) inheritance.
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One important idea attributed to Gregor Mendel is the Principle of Dominance. It basically states when two pure, but contrasting traits are crossed, the dominant trait will be expressed in the offspring. The Law of Segregation states that each gamete will receive one member of a homologous pair of chromosomes. The Law of Independent Assortment states that genetic traits are inherited independently of one another. For example, if you consider the hundreds of different traits in an organism, and then represent them with a deck of cards, when shuffling a deck of cards, you can come up with endless combinations of various traits within an organism. When Mendel worked with garden peas, the conclusions he arrived at worked for garden peas because this plant has alternate alleles for height, tall and short, with clear dominance. Also, the traits he studied were inherited independently of one another. However, other organisms don't necessarily inherit traits in the same way as pea plants. Consider height in humans. This trait is a combination of the additive effects of several gene pairs and not as easy to predict as in a pea plant. It is an example of polygenic inheritance. Two short parents can have a much taller offspring, depending on the combinations of height genes the offspring inherits. Sex-linked inheritance also deviates from Mendel's idea of the Law of Independent Assortment, because, sometimes, the X chromosome can also have linked to it the gene for hemophilia or color-blindness. Thus, while inheriting one of their sex chromosomes, a person at the same time will receive a gene for this condition. This deviates from Mendel's Second Law. Autosomal linkage deviates from Mendel's conclusions regarding Independent Assortment because if different genes on the same chromosome are close together, they may be inherited as a single unit. For example, in fruit flies the genes determining the eye color and wing length are inherited together. This is called a linkage group.
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