Ch. 14 Quiz (Exam 5)

Black eyes are dominant to orange eyes, and green skin is dominant to white skin. Sam, a MendAlien with black eyes and green skin, has a parent with orange eyes and white skin. Carole is a MendAlien with orange eyes and white skin. If Sam and Carole were to mate, the predicted phenotypic ratio of their offspring would be _____.

1 black eyes, green skin : 1 black eyes, white skin : 1 orange eyes, green skin : 1 orange eyes, white skin -Sam's genotype is BbGg, and Carole's genotype is bbgg.

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

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.

The fact that all seven of the pea plant traits studied by Mendel obeyed the principle of independent assortment most probably indicates which of the following?

All of the genes controlling the traits behaved as if they were on different chromosomes.

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.

A woman who has blood type A positive has a daughter who is type O positive and a son who is type B negative. Rh positive is a trait that shows simple dominance over Rh negative and is designated by the alleles R and r, respectively. A third gene for the MN blood group has codominant alleles M and N. Which of the following is a possible phenotype for the father?

B positive

In the following cross, the genotype of the female parent is BbGg. What is the genotype of the male parent? [Hint: B = black eyes, b = orange eyes, G = green skin, g = white skin]

BBGg -All of the offspring have black eyes, and there is a 3:1 ratio of skin color.

A black guinea pig crossed with an albino guinea pig produces 12 black offspring. When the albino is crossed with a second black one, 7 blacks and 5 albinos are obtained. What is the reasoning for this?

Black is dominant over albino

A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for tail length (T). Its genotype is HhTt. Which of the following genotypes is possible in a gamete from this organism?

HT

Which of the following do you expect if an individual is heterozygous for the sickle-cell trait?

He or she will show some symptoms of the disease. - A heterozygote will produce both normal and abnormal hemoglobin.

How are sister chromatids and homologous chromosomes different from each other?

Homologous chromosomes contain the same gene loci but may have different alleles of a particular gene. Sister chromatids are identical copies of each other produced during DNA replication

Which of the following is the meaning of the chromosome theory of inheritance as expressed in the early 20th century?

Mendelian genes are at specific loci on the chromosome and in turn, segregate during meiosis.

In his breeding experiments, Mendel first crossed true-breeding plants to produce a second generation, which were then allowed to self-pollinate to generate the offspring. How do we name these three generations?

P, F₁,F₂ -Mendel started with true-breeding P generation plants, and in a typical experiment generated two subsequental generations, called F₁and F₂.

You cross a true-breeding red-flowered snapdragon with a true-breeding white-flowered one. All of the F1 are pink. What does this say about the parental traits?

Red shows incomplete dominance over white. -Red shows incomplete dominance over white, and the F1 is therefore pink.

An inversion in a human chromosome often results in no demonstrable phenotypic effect in the individual. What else may occur?

Some abnormal gametes may be formed.

Two plants are crossed, resulting in offspring with a 3:1 ratio for a particular trait. What does this suggest?

That the parents were both heterozygous for a single trait.

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel's law of independent assortment?

The arrangement of each pair of homologous chromosomes on the metaphase plate during metaphase I is random with respect to the arrangements of other pairs.

What is crossing over?

The exchange of homologous portions of non-sister chromatids

When Thomas Hunt Morgan crossed his red-eyed F₁ generation flies to each other, the F₂ generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

The gene involved is on the X chromosome.

Which of the following is true of an X-linked gene, but not of a Y-linked gene?

The gene is present in both males and females

Which of the following differentiates between independent assortment and segregation?

The law of independent assortment requires describing two or more genes relative to one another.

In humans, what determines the sex of offspring and why?

The male gamete determines sex because each male gamete can contribute either an X or a Y chromosome

Synapsis

The pairing of homologous chromosomes that only occurs during prophase I of meiosis

Chromatids are separated from each other.

The statement is true for mitosis and meiosis II

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.

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.

Height in humans generally shows a normal (bell-shaped) distribution. What type of inheritance most likely determines height?

a combination of polygenic inheritance and environmental factors. -Several genes (polygenic inheritance) control height in humans, giving an overal normal distribution. Environmental factors such as nutrition smooth out the curve.

SRY is best described in which of the following ways?

a gene region present on the Y chromosome that triggers male development

epistatic

a phenomenon win which the expression of one gene depends on the presence of one or more modifier genes. A gene who phenotype is expressed is called epistatic, while one whose phenotype is alter or suppressed is called hypostatic.

What is an allele?

an alternate version of a gene. -A diploid organism carries two alleles for each autosomal gene. The two alleles are found at comparable locations (loci) on homologous chromosomes. The alleles may be identical or slightly different, but they affect the same genetic character.

In order to determine the genotype of a MendAlien with black eyes and green skin, you would cross this individual with a(n) _____ individual.

bbgg -This is an extension of the single character testcross you worked with in the activity on monohybrid crosses.

A phenotypic ratio of 9:3:3:1 in the offspring of a cross indicates that _____.

both parents are heterozygous for both genes -Such a result indicates that the genes assort independently and that, for each gene, the alleles exhibit a dominant/recessive relationship.

A cross between an individual with orange eyes and green skin and an individual with black eyes and white skin is an example of a _____ cross.

dihybrid -The cross is examining two characters.

Hydrangea plants of the same genotype are planted in a large flower garden. Some of the plants produce blue flowers and others pink flowers. This can be best explained by which of the following?

environmental factors such as soil pH

Consider pea plants with the genotypes GgTt and ggtt . These plants can each produce how many type(s) of gametes?

four...one -GgTt individuals can produce the following gametes: GT, Gt, gT, and gt. A ggtt plant can produce only gt

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

gametes, progeny

dihybrid cross

is a cross between F₁offspring of two individuals that differ in two traits of particular interest. For example BB x bb.

monohybrid cross

is a mating between individuals who have different alleles at one genetic locus of interest. To carry out such a cross, each parent is chosen to be homozygous or true breeding for a given trait. When a cross satisfies the conditions for a monohybrid cross, it is usually detected by a characteristic distribution of second generation (f2) offspring that is sometimes called the monohybrid ratio. Example ww x RR wR wR wR wR RR, Rw, Rw, ww

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

Mitosis results in the formation of how many cells; meiosis results in the formation of how many cells?

mitosis; 2 dipliod daughter cells meiosis; 4 haploid cells

What is the source of the extra chromosome 21 in an individual with Down syndrome?

nondisjunction or translocation in either parent

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

none

codominance

occurs when the contribuitions of both alleles are visible in the phenotype. For example in Co-dominance, a red homozygous flower and a white homozygous flower will produce offspring that have red and white spots.

incomplete dominance

occurs when the phenotype of the heterozygous genotype is distinct from and ofthen intermediate to the phenotypes of the homozygous genotypes. For example, the snapdragon flower is either homozygous for red or white. when the red homozygous flower is pair with the white homozygous flower, the results yield a pink snapdragon. (the trait are combined)

Cystic fibrosis affects the lungs, the pancreas, the digestive system, and other organs, resulting in symptoms ranging from breathing difficulties to recurrent infections. Which of the following terms best describes this?

pleiotropy

Which of the following describes the ability of a single gene to have multiple phenotypic effects?

pleiotropy

which of the following is an example of inheritance?

skin pigmentation in humans.

Law of segregation

the law of segregation states that two alleles for a gene separate during gamete formation, and end up in different gamete. in 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.

Independent assortment of chromosomes is a result of

the random and independent way in which each pair of homologous chromosomes lines up at the metaphase plate during meiosis I

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this alteration called?

translocation

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.

Various procedures can be used to detect genetic disorders before birth. Among the tests discussed in this chapter, which is the least invasive (list first), and which two allow the chromosomes of the fetus to be examined?

ultrasound imaging, chorionic villus sampling, amniocentesis -Both CVS and amniocentesis involve the preparation of a karyotype using fetal cells.

In a situation in which genes assort independently, what is the ratio of the gametes produced by an AaBB individual?

1 AB : 1 aB

In certain plants, tall is dominant to short. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short?

0

An individual heterozygous for eye color, skin color, and number of eyes mates with an individual who is homozygous recessive for all three characters; what would be the expected phenotypic ratio of their offspring? [Hint: B = black eyes, b = orange eyes; G = green skin, g = white skin; C = two eyes, c = one eye]

1 black eyes, green skin, two eyes : 1 black eyes, green skin, one eye : 1 black eyes, white skin, two eyes : 1 black eyes, white skin, one eye : 1 orange eyes, green skin, two eyes : 1 orange eyes, green skin, one eye : 1 orange eyes, white skin, two eyes : 1 orange eyes, white skin, one eye -This is a tough problem; you had to expand your Punnett square to accommodate another character. However, 1:1:1:1:1:1:1:1 ratio is the expected outcome of a BbGgCc x bbggcc cross.

Geneticists analyze pedigrees to follow the inheritance of genetically controlled conditions. Three things must be determined in a pedigree analysis:

1) The mode of inheritance of the condition. 2) The genotypes of individuals in the pedigree (as far as can be known) based on their phenotype 3) The probability that certain individuals will have the condition.

Black fur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails (t). What fraction of the progeny of crosses BbTt × BBtt will be expected to have black fur and long tails?

1/2

What do we mean when we use the terms monohybrid cross and dihybrid cross?

A dihybrid cross involves organisms that are heterozygous for two characters and a monohybrid cross involves only one.

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

AaBb, aabb -The offspring of these parents would have a phenotypic ratio of 1:1:1:1.

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.

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

False

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.

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.

Which of the following provides an example of epistasis?

In Drosophila (fruit flies), white eyes can be due to an X-linked gene or to a combination of other genes.

Which of the following is true about a plant with the genotype AABbcc?

It is homozygous at two loci. -An organism having a pair of identical alleles at a given locus is said to be homozygous for that locus. Here, the plant is homozygous at loci A and C.

Folk singer Woody Guthrie died of Huntington's disease, an autosomal dominant disorder. Which statement below must be true?

It is very likely that at least one of Woody Guthrie's parents also have had the allele for Huntington's disease. -Unless the disease is caused by a new mutation, which is quite rare, individuals with a dominant condition must have inherited the dominant allele from one of their parents. As it happens, Guthrie's mother also died of Huntington's disease.

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.

A BbGg x bbgg cross yields a phenotypic ratio of approximately 5 black eyes, green skin : 5 orange eyes, white skin : 1 black eyes, white skin : 1 orange eyes, green skin. Which of the following best explains these results?

Mendel's law of independent assortment is being violated. -If the genes for eye color and skin color assorted independently, then the outcome of this cross would have been a 1:1:1:1 ratio.

Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?

XCXc and XCY