Mendel’s Law

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    • #17925

      Having issues with determining the ratio.

      Describe the phenotypic and genotypic ratios for the F2 generation if pea plants with restricted yellow pods are crossed with true-breeding inflated green pods in the original cross and then the F1 generation is crossed.

    • #115486

      unless you tell us which one is dominant/recesive we will hardly give you any advice

    • #115583

      Before reviewing these three laws, it will be helpful to define some of the terms used in talking about Mendel’s laws of inheritance. Most of these terms were invented not by Mendel, but by biologists some years after his research was originally published.

      Genes are the units in which characteristics are passed from one generation to the next. For example, a plant with red flowers must carry a gene for that characteristic.

      A gene for any given characteristic may occur in one of two forms, called the alleles (pronounced uh-LEELZ) of that gene. For example, the gene for color in pea plants can occur in the form (allele) for a white flower or in the form (allele) for a red color.

      The first step that takes place in reproduction is for the sex cells in plants to divide into two halves, called gametes. The next step is for the gametes from the male plant to combine with the gametes of the female plant to produce a fertilized egg. That fertilized egg is called a zygote. A zygote contains genetic information from both parents.

      For example, a zygote might contain one allele for white flowers and one allele for red flowers. The plant that develops from that zygote would said to be heterozygous for that trait since its gene for flower color has two different alleles. If the zygote contains a gene with two identical alleles, it is said to be homozygous.

      The application of Mendel’s three laws makes it possible to predict the characteristics of offspring produced by parents of known genetic composition. The picture on page 1248, for example, shows the cross between a sweet pea plant with red flowers (RR) and one with white flowers (rr). Notice that the genes from the two parents will segregate to produce the corresponding alleles:

      RR → R + R and rr → r + r

      There are, then, four ways in which those alleles can recombine, as shown in the same picture. However, all four combinations produce the same result: R + r → Rr. In every case, the gene formed will consist of an allele for red (R) and an allele for "not red" (r).

      The drawing at the right in the picture on page 1248 shows what happens when two plants from the first generation are crossed with each other. Again, the alleles of each plant separate from each other:

      Rr → R + r

      Again, the alleles can recombine in four ways. In this case, however, the results are different from those in the first generation. The possible results of these combinations are two Rr combinations, one RR combination, and one rr combination. Since R is dominant over r, three of the four combinations will produce plants with red flowers and one (the rr option) will product plants with non-red (white) flowers.

      Biologists have discovered that Mendel’s laws are simplifications of processes that are sometimes much more complex than the examples given here. However, those laws still form an important foundation for the science of genetics.

      Read more: … z3Kons4r1s

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