mastering biology assignment 11

Two mice are heterozygous for albinism (Aa) . The dominant allele (A) codes for normal pigmentation, and the recessive allele (a) codes for no pigmentation. What percentage of their offspring would have an albino phenotype?

25 The offspring would be in a 3:1 ratio of normally pigmented mice to albino mice.

Which of the following parental genotypes would yield a 1:1:1:1 phenotypic ratio in the offspring?

AaBb, aabb

Which statement most accurately describes the pattern of inheritance for a human disease caused by a dominant allele on the X chromosome (assuming the disease allele is rare)?

Affected fathers have all affected daughters, but no affected sons. All daughters get an X chromosome from their father (which must carry the disease allele in this case), and all sons get their single X chromosome from their unaffected mother.

What is the difference between heterozygous and homozygous individuals?

All of the gametes from a homozygote carry the same version of the gene while those of a heterozygote will differ. Since homozygotes carry two identical copies of a gene, all of the gametes will carry the same version. Heterozygotes have two different versions, so there will be two different types of gametes.

Which of the following statements most accurately describes the process of independent assortment?

Alleles of different genes segregate from one another in a random manner. The random distribution of alleles is required for independent assortment.

How could the botanist best determine whether the genotype of the green-pod plant is homozygous or heterozygous?

Cross the green-pod plant with a yellow-pod plant. A cross between a plant of unknown genotype and one that is known to be homozygous recessive is called a test cross because the recessive homozygote tests whether there are any recessive alleles in the unknown. Because the recessive homozygote will contribute an allele for the recessive characteristic to each offspring, the second allele (from the unknown genotype) will determine the offspring's phenotype.

The alleles found in haploid organisms cannot be dominant or recessive. Why?

Dominance and recessiveness describe interactions between two alleles of the same gene in the same

How do cells acquire homologous chromosome pairs that carry the alleles that are independently assorted?

Fusion of gametes During fertilization, gametes bring together homologous chromosomes to generate a diploid individual.

In peas, the allele for yellow seeds (Y) is dominant to the allele for green seeds (y). What would be the genotype and phenotype ratios of offspring from a cross between Yy and yy individuals?

Genotype: ½ Yy : ½ yy; Phenotype: ½ yellow : ½ green

How does crossing over break up linkage between alleles?

It involves a physical exchange of segments from homologous chromosomes.

Why can you infer that individuals that are "pure line" are homozygous for the gene in question?

No other phenotype arises in a pure-line population because no other alleles are present.

Which event in meiosis accounts for Mendel's principle of independent assortment?

Nonhomologous chromosomes line up independently during meiosis I. This event explains why alleles on nonhomologous (different) chromosomes assort independently, and explains why gametes contain random assortments of maternal and paternal chromosomes.

Which of the following is the strongest evidence that a trait might be influenced by polygenic inheritance?

The trait shows quantitative variation.

In studies of how traits are inherited, what makes certain species candidates for model organisms?

They are easy to maintain, have a short life cycle, produce many offspring, and yield data that are relevant to many other organisms.

True or false? In diploid organisms, a dominant phenotype will only be expressed if the individual is homozygous dominant for that trait.

false A dominant phenotype is indeed expressed if the individual is homozygous dominant for that trait, but the dominant phenotype is also expressed if the individual is heterozygous for the trait. In fact, heterozygous expression is the definition of dominant.

True or false? The principle of independent assortment is best illustrated by events that take place during metaphase II, during which sister chromatids segregate independently of each other.

false The principle of independent assortment is best illustrated by events that take place during metaphase I, during which nonhomologous chromosomes segregate independently of each other.

When constructing a Punnett square, the symbols on the outside of the boxes represent _______, while those inside the boxes represent _______.

gametes, progeny The Punnett square is representing all of the possible combinations of the gametes from each parent, with the progeny represented in the interior of each box.

Suppose that the botanist carried out the test cross described in Parts A and B and determined that the original green-pod plant was heterozygous (Gg). Which of Mendel's findings does her test cross illustrate?

law of segregation The law of segregation states that the two alleles for a gene separate during gamete formation, and end up in different gametes. In the case of the heterozygous green-pod plant (Gg), one gamete will receive the dominant allele (G), and the other gamete will receive the recessive allele (g). The law of segregation accounts for the prediction that 50% of the offspring of the test cross will have green pods and 50% will have yellow pods.

What process is responsible for the independent assortment of alleles?

meiosis The role of meiosis is to separate homologous chromosomes and their respective alleles, which are assorted in an independent manner.

During which part of meiosis (meiosis I or meiosis II) do the two alleles of a gene separate? During which phase does the separation occur?

meiosis 1, anaphase Alleles separate from one another during anaphase of meiosis I, when the homologous pairs of chromosomes separate.

If an organism with the genotype AaBb produces gametes, what proportion of the gametes would be Bb?

none Alleles of the same gene must separate during gamete formation; thus, the two B alleles would be distributed to different gametes.

Which event in meiosis accounts for Mendel's principal of segregation?

separation of homologs at anaphase I The physical separation of alleles on the two homologs in anaphase of meiosis I explains why each gamete contains one allele of each gene.

True or false? The same phenotype can be produced by more than one genotype.

true Since there exist dominant and recessive versions of many genes, a phenotype that is based upon the dominant version will be expressed in both homozygous (AA) and heterozygous (Aa) genotypes.

A tall, purple-flowered pea plant (TtPp) is allowed to self-pollinate. (The recessive alleles code for short plants and white flowers.) The phenotypic ratio of the resulting offspring is 9:3:3:1. What is the genotype of the plant whose phenotype appeared once out of every 16 offspring (the "1" in the 9:3:3:1 ratio)?

ttpp The smallest phenotypic group consists of the homozygous recessive plants, which in this case are short and white flowered.

How many genetically unique types of gametes could be produced by an individual with the genotype RrYY?

two The gametes would be either RY or rY.

Imagine that you perform fruit fly crosses with different pairs of three X-linked traits specified by genes x, y, and z. You observe the following recombinant frequencies for the various gene pairs: xy= 6.9% yz= 7.6% xz= 0.7% What is the most likely gene order?

yxz This is the only order where the recombination distances between each gene pair (the physical distances along the linear chromosome that produce the observed recombinant frequencies) sum correctly.