Ch. 12 Biology Study Guide

How many different gametes can be produced by a tall, yellow-seeded, purple-flowered, and wrinkled-seeded pea plant (TtYyPprr)?

8

A gardener crosses a true-breeding tall tomato plant bearing red fruit with a true-breeding dwarf tomato plant with yellow fruit. In tomatoes, tall vine (T) is dominant to dwarf vine (t) and red fruit (R) is dominant to yellow fruit (r). Assume that the two genes controlling the "tall vine" and "red fruit" traits are on two different pairs of chromosomes. What are the expected phenotype ratios in the F2 generation?

9 tall vine/red fruit; 3 tall vine/yellow fruit; 3 dwarf vine/red fruit; 1 dwarf vine/yellow fruit

The genotype of plants with the recessive phenotype of wrinkled seeds is always homozygous. However, when an individual plant expresses the dominant phenotype of round seeds, it can have either the genotype RR or Rr. How could you test whether the dominant individual is a true breeder (RR)? Explain.

A test cross could be performed where the plant of unknown genotype with the dominant phenotype is crossed with a plant expressing the recessive phenotype. If any offspring of this cross express the recessive phenotype, the dominant parent plant's genotype is assumed to be heterozygous (Rr).

The Punnett square describes the potential offspring of a cross. What phenotypes will be shown by the offspring?

All offspring will show the dominant phenotype for this trait.

What happens to the two cells formed at the end of meiosis I? Choose two correct answers.

Four haploid daughter cells are formed during meiosis II. Chromosomes do not replicate and the paired chromatids separate.

Mitochondria are often described as the powerhouses of the cell. Genetic disorders can result when mitochondrial mutations occur. For example, a condition called Kearns-Sayre syndrome is caused by deletions in the mitochondrial DNA. This genetic disorder causes weakness of the muscles and other symptoms because the mitochondria are not able to provide sufficient energy to the cells. The diagram shows the possible phenotypes of children from parents who have the disease. How is Kearns-Sayre syndrome inherited? Select the best explanation.

Genetic disorders caused by mitochondrial mutations are examples of cytoplasmic inheritance. Only mothers transmit mitochondrial genetic disorders to their children. The male gametes have little cytoplasm. They do not contribute mitochondria to the embryos.

Mendel was a careful researcher who studied the inheritance of certain traits in garden peas. What are some of the research practices Mendel used? Choose all that apply.

He controlled variables by studying one or two traits at a time. He analyzed his data mathematically. He controlled variables by studying one or two traits at a time.

Red blood cells carry antigens on their surfaces coded for by alleles of the gene designated by the letter I. IA is dominant to i and produces antigen A on the surface of red blood cells. The IB allele is also dominant to the i allele and produces antigen B on the surface of red blood cells. The i allele does not produce surface antigens. What types of inheritance are represented by the genetics of human blood types? Select all of the answers that apply.

IA and IB show incomplete dominance because both alleles are partially expressed in blood type A and B. The human blood type gene is an example of a gene with multiple alleles, IA, IB, i.

Read each of the sentences that describe a phase of mitosis or meiosis I. Then decide if is a phase of mitosis or meiosis I. Homologous chromosomes line up at the center of the cell.

Meiosis I

Read each of the sentences that describe a phase of mitosis or meiosis I. Then decide if is a phase of mitosis or meiosis I. Homologous chromosomes pair to form a tetrad and cross over.

Meiosis I

Read each of the sentences that describe a phase of mitosis or meiosis I. Then decide if is a phase of mitosis or meiosis I. Homologous pairs separate and move towards opposite poles of the cell.

Meiosis I

Read each of the sentences that describe a phase of mitosis or meiosis I. Then decide if is a phase of mitosis or meiosis I. Two genetically not identical, haploid daughter cells are formed.

Meiosis I

Read each of the sentences that describe a phase of mitosis or meiosis I. Then decide if is a phase of mitosis or meiosis I. Replicated chromosomes line up at the center of the cell.

Mitosis

Read each of the sentences that describe a phase of mitosis or meiosis I. Then decide if is a phase of mitosis or meiosis I. Sister chromatids separate and move to opposite poles.

Mitosis

Read each of the sentences that describe a phase of mitosis or meiosis I. Then decide if is a phase of mitosis or meiosis I. Two genetically identical, diploid daughter cells are formed.

Mitosis

Coat color in rabbits is inherited by multiple alleles for a single gene. The table describes the alleles and their inheritance. Would it be possible to obtain a rabbit with Chinchilla coat color if one parent is white and the other parent has a Himalayan coat color?

No, because the parents have no alleles for Chinchilla.

A two- trait cross is equivalent to two monohybrid crosses. To calculate the combined genotype probability of the offspring, each trait is considered separately, and then the individual probabilities are multiplied together. A yellow seeded, purple flowered heterozygous plant (YyPp), is crossed with a green seeded, white flower plant (yypp). (Y = yellow seed allele; y = green seed allele; P = purple flower allele; p = white flower allele) What is the probability that an offspring of this cross produces plants with green seeds and white flower phenotypes? Calculate the probabilities and complete the table.

See the image for the correct answer.

A gardener crosses a true-breeding tall tomato plant bearing red fruit with a true-breeding dwarf tomato plant with yellow fruit. In tomatoes, tall vine (T) is dominant to dwarf vine (t) and red fruit (R) is dominant to yellow fruit (r). Predict the phenotypes and genotypes of the F1 generation.

Since the tall vine and the red fruit traits are dominant to the dwarf vine and the yellow fruit alleles respectively, and the parent plants are true-breeding, the F1 plants will all express the phenotype tall vine and red fruit. The F1 dihybrid genotype is TtRr.

One dog is heterozygous for black fur (Bb), and its mate is homozygous for blonde fur (bb). What is the probability of one of their puppies having black fur? Explain.

The probability is 50 percent. In this monohybrid cross, there can be 2Bb and 2bb genotypes in the offspring, and 2 black and 2 blond phenotypes, because the black dog produces gametes with either the B or the b allele, and the blond dog produces gametes with the b allele.

In cattle, if a red animal is crossed with a white one, a mixture of red and white color, called roan, is produced in the F1 generation. Crosses between animals in the F1 generation produce white, roan, and red cattle. Describe the pattern of inheritance in these types of cattle.

This is an example of incomplete dominance of the R and r alleles. The Rr genotype of the F1 individuals with roan coats show an intermediate phenotype. Neither allele is dominant or recessive. The cross between two roans of the F1 generation produces a 1:2:1 F2 ratio of white: roan: red.

Mendel studied 7 traits in pea plants. One of the monohybrid crosses he made was between plants with round seeds (R) and plants with wrinkled seeds (r). What was a conclusion that Mendel drew from the F2 generation of this cross?

Three fourths of the F2 plants show the round seed phenotype and carry the dominant allele for roundness.

A geneticist crossed tall pea plants and obtained 971 tall pea plants and 315 short pea plants in the F1 generation. What were the genotypes of the parents that produced the offspring in the Punnett square shown, if T is the allele for tall, and t is the allele for short?

Tt

These homologous chromosomes carry different alleles of the wild type and mutant type in the fruit fly Drosophila. A cell with the homologous chromosomes undergoes meiosis, and gametes are produced. Is it possible for a chromosome of a gamete to contain the alleles for gray body and brown eyes?

Yes, because homologous chromosomes may exchange segments by crossing over during meiosis.

Which two genes are most likely to be affected by a crossing-over event?

a pair of genes located at opposite ends of a chromosome

Choose the words from the word box below to finish the paragraph. (Some words may be used more than once and some not at all.) A human cell that carries a double set of chromosomes is called a __________ cell. The cell contains 2N = 46, number of chromosomes. One __________ of each __________ is located on each _______________ chromosome. In sexual reproduction, meiosis produces __________ gametes with one of each kind of chromosome. In humans, these cells contain __________ number of chromosomes.

diploid, allele, gene, homologous, haploid, N = 23

The phenotype of an organism is only partially determined by genotype. Choose one word from each row in the word box to complete the paragraph below. (Some words may be used more than once.) In order to fly effectively, the body temperature of the Western white butterfly needs to be 28-40oC. ____________ pigmentation allows a butterfly to reach the warm body temperature faster. In hot summer months, ____________ pigmentation prevents the butterflies from overheating. In this case, ____________ conditions affect the ____________ and influence ____________ of the butterfly.

more, less, environmental, phenotype, genetically determined traits

A plant's stem lengths were graphed from the F1 generation. Seven categories of stem length phenotypes were observed. What pattern of inheritance is suggested by the graph?

polygenic inheritance

Choose the words from the word box below to finish the paragraph. (Some words may be used more than once and some not at all.) Meiosis is a process that ____________ chromosomes to the ____________ number, provides ____________, and ensures the correct distribution of ____________ into the ____________.

reduces, haploid, genetic variation, chromosomes, gametes