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Ch. 14 - Mendel and the Gene
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook
Chapter 14, Problem 12d

Suppose you are heterozygous for two genes that are located on different chromosomes. You carry alleles A and a for one gene and alleles B and b for the other. On the diagram, identify the events responsible for the principle of segregation and the principle of independent assortment.

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Begin by understanding the principle of segregation, which states that alleles for a gene separate during gamete formation. This occurs during meiosis I when homologous chromosomes are separated into different cells.
Next, identify the principle of independent assortment, which states that alleles of different genes are distributed independently of one another during gamete formation. This is due to the random orientation of homologous chromosome pairs during metaphase I of meiosis.
Visualize meiosis I: During metaphase I, homologous chromosomes line up at the equatorial plane. For the alleles A and a, one chromosome carries A and the other carries a. Similarly, for alleles B and b, one chromosome carries B and the other carries b.
During anaphase I, homologous chromosomes are pulled apart to opposite poles of the cell. This is where segregation occurs, as each gamete receives one allele from each gene pair.
Finally, consider the independent assortment: Since the chromosomes carrying A/a and B/b are on different chromosomes, their orientation during metaphase I is random, leading to different combinations of alleles in the gametes. This randomness is the basis for independent assortment.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Principle of Segregation

The principle of segregation states that during the formation of gametes, the two alleles for a gene separate so that each gamete receives only one allele. This occurs during meiosis, specifically in anaphase I, when homologous chromosomes are pulled apart, ensuring that each gamete carries only one allele from each gene pair.
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Law of Segregation

Principle of Independent Assortment

The principle of independent assortment describes how alleles of different genes are distributed independently of one another into gametes. This occurs during metaphase I of meiosis when homologous chromosome pairs align randomly at the cell's equator, leading to a variety of possible genetic combinations in the resulting gametes.
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Meiosis

Meiosis is a type of cell division that reduces the chromosome number by half, creating four genetically diverse haploid cells from one diploid cell. It consists of two stages, meiosis I and meiosis II, and is crucial for sexual reproduction, ensuring genetic diversity through processes like crossing over and independent assortment.
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Related Practice
Textbook Question

Suppose you are heterozygous for two genes that are located on different chromosomes. You carry alleles A and a for one gene and alleles B and b for the other. Draw a diagram illustrating what happens to these genes and alleles when meiosis occurs in your reproductive tissues.

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Textbook Question

Suppose you are heterozygous for two genes that are located on different chromosomes. You carry alleles A and a for one gene and alleles B and b for the other. Label the stages of meiosis, the homologous chromosomes, sister chromatids, nonhomologous chromosomes, genes, and alleles.

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Textbook Question

Suppose you are heterozygous for two genes that are located on different chromosomes. You carry alleles A and a for one gene and alleles B and b for the other. Be sure to list all the genetically different gametes that could form and indicate how frequently each type should be observed.

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Textbook Question

The blending inheritance hypothesis proposed that the genetic material from parents is mixed in the offspring. As a result, traits of offspring and later descendants should lie between the phenotypes of parents. Mendel, in contrast, proposed that genes are discrete and that their integrity is maintained in the offspring and in subsequent generations. Suppose the year is 1890. You are a horse breeder who has just read Mendel's paper. You don't believe his results, however, because you often work with cremello (very light-colored) and chestnut (reddish-brown) horses. You know that when you breed a cremello individual from a pure-breeding line with a chestnut individual from a pure-breeding line, the offspring are palomino—meaning they have an intermediate (golden-yellow) body color. What additional cross would you do to test whether Mendel's model is valid in the case of genes for horse color? According to his model, what offspring phenotype frequencies would you get from your experimental cross? Explain why your cross would test Mendel's model versus blending inheritance.

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Textbook Question

Two mothers give birth to sons at the same time in a busy hospital. The son of couple 1 is afflicted with hemophilia A, which is a recessive X-linked disease. Neither parent has the disease. Couple 2 has a normal son even though the father has hemophilia A. The two couples sue the hospital in court, claiming that a careless staff member swapped their babies at birth. You appear in court as an expert witness. What do you tell the jury? Make a diagram that you can submit to the jury.

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Textbook Question

You have crossed two Drosophila melanogaster individuals that have long wings and red eyes—the wild-type phenotype. In the progeny, curved wings and lozenge eyes mutant phenotypes appear as follows According to these data, is the curved-wing allele autosomal recessive, autosomal dominant, sex-linked recessive, or sex-linked dominant?

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