answers2e_ch10 - Mastering Concepts 10.1 1 Describe the...

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Mastering Concepts 10.1 1. Describe the relationships among chromosomes, DNA, genes, and alleles. Chromosomes contain tightly packed DNA and associated proteins. DNA are the strands of genetic material that contains genes, sequences of nucleotides that code for amino acids. Those genes come in varieties called alleles. 2. How do meiosis, fertilization, diploid cells, and haploid cells interact in a sexual life cycle? Meiosis in the adult organism creates the haploid gamete cells that combine during fertilization to form the diploid zygote cell. That cell undergoes mitosis to make the cells that are necessary for growth into the adult form. 10.2 1. Why did Gregor Mendel choose pea plants as his experimental organism? Mendel chose pea plants because they are easy to grow, develop quickly, produce many offspring, and have many traits that appear in two alternate forms that are easy to distinguish. It also is easy to hand-pollinate pea plants, so an investigator can control which plants mate with one another. 2. Distinguish between dominant and recessive; heterozygous and homozygous; phenotype and genotype; wild type and mutant. Dominant alleles appear in a phenotype whenever they are present; recessive alleles contribute to the phenotype only if no dominant alleles are present. An individual is homozygous for a gene if both alleles are identical; in a heterozygous individual, the two alleles for a gene are different. An organism’s phenotype is its appearance; the genotype is the alleles an individual possesses. The wild type allele is the most common form of a gene in a population; a mutant allele arises when a gene undergoes a mutation. 3. Define the P, F 1 , and F 2 generations. The P generation is the parental or starting generation. F 1 and F 2 refer to the first and second generations of offspring, respectively. 10.3 1. What is a monohybrid cross, and what are the genotypic and phenotypic ratios expected in the offspring of the cross?
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A monohybrid cross is a mating between two individuals that are both heterozygous for one gene. The genotypic ratio expected in a monohybrid cross is 1:2:1; the phenotypic ratio is 3:1. 2. How are Punnett squares helpful in following inheritance of single genes? Punnett squares show the genotypes of each parent as well as the genotypes of potential offspring. Phenotypic and genotypic ratios of offspring can be predicted from the data in Punnett squares. 3. What is a test cross, and why is it useful? A test cross is a mating between a homozygous recessive individual and an individual of unknown genotype. The genotype of the unknown parent can be deduced from the ratio of phenotypes in the F 1 generation. 4. How does the law of segregation reflect the events of meiosis? The law of segregation reflects the movement of homologous chromosomes into separate cells during meiosis I.
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