Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 10
10.1
1. 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. 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 individual
possesses. The wild type allele is the most common form of a gene in a population; a mutant
allele is different from the norm.
10.2
1. 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. 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. A testcross 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 F1 generation.
4. The law of segregation reflects the movement of homologous chromosomes into separate cells
during meiosis I.
10.3
1. In a dihybrid cross, two individuals that are heterozygous for two genes are mated. The
phenotypic ratio that is expected is 9:3:3:1.
2. The law of independent assortment reflects the fact that each homologous pair of
chromosomes aligns independently of other chromosome pairs during metaphase I of meiosis.
3. The product rule allows you to estimate the odds that an offspring will have a certain
combination of alleles for multiple genes, by multiplying the probability that each separate event
will occur.
10.4
1. Incomplete dominance and codominance produce phenotypes that are intermediate between
those produced by homozygous dominant or homozygous recessive individuals.
2. Pleiotropy occurs when a gene produces multiple phenotypic expressions. Pleiotropy results
when the protein encoded by a gene enters several different biochemical pathways or affects
more than one body part or process.
3. Each gene encodes one protein, but many different proteins may interact in a single metabolic
pathway. A mutation in a gene encoding any of these proteins may produce a flawed metabolic
pathway. In this way, different genotypes can produce the same phenotype (failure of the
metabolic pathway to operate properly).
4. In epistasis, one gene affects the expression of another. The gene interaction may cause some
phenotypes to appear to be missing from a population.
10.5
1. Environment can affect a phenotype in a variety of ways. Temperature can influence gene
expression of temperature-sensitive alleles; infectious agents can intensify a genetic disorder;
upbringing and nourishment will affect temperament and physical health.
2. A polygenic trait is one that is controlled by many genes.