Since there is a genetic explanation for short sleepers, you would expect.

a) That this trait appears more frequently among family members

b) A higher percentage of women to be short sleepers

c) That people can learn to be short sleepers

d) That short sleepers have higher metabolisms

a) That this trait appears more frequently among family members

1) With or together wight:

2) To love:

3) Change, turn, move:

4) Against:

5) To:

6) Difficult, painful:

7) Of neither gender or type:

8) Many:

9) From, out of, remove:

10) Not:

1) Co-

2) -Phil (or philo-)

3) Trop- (or -tropic)

4) anti-

5) ad-

6) dys-

7) neutr-

8) poly-

9) de-

10) non-

1) One-half

2) enzyme

3) change, after

4) three

5) blood

6) across

7) different, other

8) milk

9) within

1) semi-

2) -ase

3) meta-

4) tri-

5) hem- (or hemato-)

6) trans-

7) hetero-

8) lact-

9) intra-

In mammals, hair/fur color is determined by the expression of a number of different genes, each of which has two or more alleles. According to Mendel’s second law, unlinked genes (those that are either on different chromosomes or on the same chromosome but very distant from one another) assort independently because they align independently on the spindle during metaphase I of meiosis. In this tutorial, you will solve genetics problems related to the inheritance of fur color in mice.

Part A - A trait governed by two or more genes

In mice, agouti fur is a dominant trait resulting in individual hairs having a light band of pigment on an otherwise dark hair shaft. A mouse with agouti fur is shown here, along with a mouse with solid color fur, which is the recessive phenotype (A = agouti; a = solid color).

What would be the expected frequency of agouti brown offspring in the litter?

a) 1/2

b) 1/8

c) 3/16

d) 1/4

e) 9/16

f) not enough information given

c) 3/16

Because the two traits are determined by unlinked genes, they assort independently. As a result, you need to use the multiplication rule to calculate the probability of agouti brown offspring (A_ bb) from AaBb parents. The probability of A_offspring is 3/4, and the probability of bb offspring is 1/4. The combined probability is therefore 3/4 x 1/4 = 3/16.

In addition to A and a, the “agouti” gene has a third allele, A^Y . Here is some information about the inheritance of the A^Y allele.

• The A^Y allele is dominant to both A and a.
• The homozygous genotype (A^YA^Y ) results in lethality before birth.
• The heterozygous genotypes (A^YA or A^Ya) result in yellow fur color, regardless of which alleles are present for the B/b gene. (This effect exhibited by the A^Y allele is known as epistasis--when the expression of one gene masks the expression of a second gene.)

Suppose you mate two mice with the genotypes A^YaBb x A^YaBb . Considering only the live-bornoffspring, what would be the expected frequency of mice with yellow fur? (For help getting started, see Hint 1.)

Express your answer as a fraction using the slash symbol and no spaces (for example, 1/16).

Answer: 2/3

Because the presence of the A^Y allele is epistatic to (masks expression of) the B/b gene, the B/b gene does not need to be taken into consideration in this problem. For the A^Ya x A^Ya cross, 1/4 of the offspring would have the A^YA^Y genotype, which is lethal before birth. For the live-born offspring, 2/3 would be A^Ya, and thus have yellow fur.

In the same mouse species, a third unlinked gene (gene C/c) also has an epistatic effect on fur color. The presence of the dominant allele C (for color), allows the A/a and B/b genes to be expressed normally. The presence of two recessive alleles (cc), on the other hand, prevents any pigment from being formed, resulting in an albino (white) mouse.

Match the phenotypes on the labels at left to the genotypes listed below. Labels can be used once, more than once, or not at all.

Because the C/c gene is epistatic to both the A/a and B/b genes, any offspring with the ccallele combination will be albino. Otherwise, the A/a and B/b genes are expressed normally.

In the same mouse species, a fourth unlinked gene (gene P/p) also affects fur color.

• For mice that are either homozygous dominant (PP) or heterozygous (Pp), the organism’s fur color is dictated by the other three genes (A/a, B/b, and C/c).
• For mice that are homozygous recessive (pp), large patches of the organism’s fur are white. This condition is called piebaldism.

In a cross between two mice that are heterozygous for agouti, black, color, and piebaldism, what is the probability that offspring will have solid black fur along with large patches of white fur? (Hint: Consider each gene separately; then use the multiplication rule. For more help getting started, see Hint 1.)

Express your answer as a fraction using the slash symbol and no spaces (for example, 3/16).

Answer: 9/256

Because each gene segregates independently, you need to determine the probability of each genotype independently and then multiply the four probabilities together. The probability of offspring with solid color (aa) is 1/4; the probability of offspring with black fur (BBor Bb) is 3/4; the probability of colored fur (CC or Cc) is 3/4; and the probability of piebald, or white patches (pp), is 1/4. The combined probability is 1/4 x 3/4 x 3/4 x 1/4= 9/256.

What is the difference between heterozygous and homozygous individuals?

a) Homozygotes have one chromosome while heterozygotes have two similar chromosomes.

b) The homozygote will express the dominant trait and the heterozygote will express the recessive trait.

c) All of the gametes from a homozygote carry the same version of the gene while those of a heterozygote will differ.

d) Heterozygotes carry two copies of a gene while homozygotes only carry one.

c) 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.

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

a) gametes, parents

b) progeny, gametes

c) parents, gametes

d) gametes, progeny

d) 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.

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

a) True

b) False

a) 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.

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

a) True

b) False

b) 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.

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

a) 3/4

b) None

c) 1/4

d) 1/2

b) None

Alleles of the same gene must separate during gamete formation; thus, the two B alleles would be distributed to different gametes.

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?

a) 75

b) 100

c) 25

d) 50

c) 25

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

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)?

a) ttpp

b) TTPP

c) TtPp

d) TTpp

a) ttpp

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

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

a) Cross the green-pod plant with a yellow-pod plant.

b) Cross the green-pod plant with another green-pod plant.

c) Self-pollinate the green-pod plant.

a) 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.

Punnett squares can be used to predict the two possible outcomes of the botanist’s test cross. The Punnett square on the left shows the predicted result if the unknown plant is homozygous (GG); the Punnett square on the right shows the predicted result if the unknown plant is heterozygous (Gg).Drag the labels to the correct locations on the Punnett squares. (G is the symbol for the green-pod allele and g is the symbol for the yellow-pod allele.) You can use a label once, more than once, or not at all.

The genotypes in a Punnett square show all the possible combinations of alleles in offspring that could result from the particular cross. A Punnett square reveals the expected probabilities of each genotype among the offspring. For example, the Punnett square on the right reveals that there is a 50% chance that each offspring will have green pods and a 50% chance that each offspring will have yellow pods.

This botanist used the same logic to reach her conclusions as Mendel used in his experiments.

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?

a) law of segregation

b) law of independent assortment

c) linkage

d) chromosome theory of inheritance

a) 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.

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?State your answer as meiosis I or meiosis II followed by a comma and the name of the phase (for example, if your answer is meiosis II and metaphase, enter meiosis II, metaphase).

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