Mastering Bio HW 3

Assuming that both parents are heterozygous for the gene that causes the disease, what is the probability that the second child will also have the disease? Express your answer as a fraction using the slash symbol and no spaces (for example, 1/2).

1/16

Two organisms with genotype AaBbCcDdEE mate. These loci are all independent. What fraction of the offspring will have the same genotype as the parents?

1/16 Breaking the question down into individual loci makes it simpler. The offspring of Aa ×Aa will be Aa 50% (one-half) of the time. The same is true for Bb, Cc, and Dd. Two EE individuals can only have EE offspring, so that probability is 1. The chance of an offspring being identical to the parent is therefore (1/2)4, or 1/16.

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.

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). A separate gene, which is not linked to the agouti gene, can result in either a dominant black pigment or a recessive brown pigment (B = black; b = brown). A litter of mice from the mating of two agouti black parents includes offspring with the following fur colors: solid color, black solid color, brown (sometimes called chocolate) agouti black agouti brown (sometimes called cinnamon) What would be the expected frequency of agouti brown offspring in the litter?

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.

What number and types of chromosomes are found in a human somatic cell?

44 autosomes and 2 sex chromosomes Human somatic cells contain 22 pairs of autosomes and either two X chromosomes (in females) or an X and a Y chromosome (in males).

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.

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.

Albino (b) is a recessive trait; black (B) is a dominant trait.

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.

What are the genotypes of the parents in the first cross (the cross that produced 12 black offspring)?

BB x bb

Two sister chromatids are joined at the centromere prior to meiosis. Which statement is correct?

Barring mutation, the two sister chromatids must be identical.

What are the genotypes of the parents in the second cross (the cross that produced 7 black and 5 albino offspring)?

Bb x bb

A botanist has acquired a group of sweet pea plants. All of the plants have yellow pea pods (the recessive trait), except for one, which has green pea pods (the dominant trait). Pea pod color is a trait caused by a single gene. In this tutorial, you will determine how the botanist can identify the genotype of the green pea pod, and how this relates to Mendel's laws and meiosis. 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 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.

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 process produces cells containing pairs of homologous chromosomes?

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

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. One homologous chromosome comes from the father, and the other comes from the mother. Sister chromatids are identical copies of each other.

Select the correct explanation for the fact that a carrier of a recessive genetic disorder does not have the disorder.

In a recessive disorder, only a single functioning allele is necessary to determine a normal phenotype.

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.

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.

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 subsequent generations, called F1 and F2.

Look at the Punnett square, which shows the predicted offspring of the F2 generation from a cross between a plant with yellow-round seeds (YYRR) and a plant with green-wrinkled seeds (yyrr). Select the correct statement about wrinkled yellow seeds in the F2 generation.

The chance that an individual taken at random from the F2 generation produces wrinkled seeds is 25% and the chance that the same individual produces yellow seeds is 75%.

Each chromosome in this homologous pair possesses a different allele for flower color. Which statement about this homologous pair of chromosomes is correct?

These homologous chromosomes represent a maternal and a paternal chromosome. Homologous chromosomes initially come together during fertilization with the contribution of a set of chromosomes from the sperm and the egg.

When a dominant allele coexists with a recessive allele in a heterozygote individual, how do they interact with each other?

They do not interact at all.

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.

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

Two ry or RY

A human cell containing 22 autosomes and a Y chromosome is

a sperm

What is an allele?

an alternative 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.

Consider pea plants with the genotypes GgTt and ggtt . How many type(s) of gametes will each plant produce?

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

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 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.

What are the genotypes of the gametes and offspring in the second cross?

gametes: 1/2 B and 1/2 b (heterozygous parent) and b; offspring: 1/2 Bb and 1/2 bb

What are the genotypes of the gametes and offspring in the first cross?

gametes: B and b; offspring: all Bb

Mendel worked _____.

in a monastery Mendel was a monk who worked in his monastery garden.

Genetic variation occurs when chromosomes are shuffled in fertilization and what other process?.

meiosis Variation is produced as a result of independent assortment and crossing over.

What is crossing over?

the exchange of homologous portions of nonsister chromatids The result is new combinations of genetic material (genetic recombination).

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.