Genetics Ch. 7 Assignment

A tall (T) tomato plant with mottled (m) leaves is crossed with a short (t) plant with normal (M) leaves. The F1 offspring are all tall, normal leafed plants.You cross the F1 plants with a short, mottled leafed plant. You observe the following progeny phenotypes: Tall, mottled leaves: 395 Short, normal leaves: 400 Tall, normal leaves: 105 Short, mottle leaves: 100 You propose a null hypothesis: The genes assort independently. What would be the expected values from this hypothesis?

Tall mottled 250, Short normal leaves 250, Tall normal leaves 250, Short mottled leaves 250

A tetrad is made up of _____.

two homologous chromosomes, each consisting of two chromatids

If a gray-bodied, red-eyed female with genotype Xy+w+Xyw were mated to a gray-bodied, red-eyed male with genotype Xy+w+Y, which phenotypic class would be counted as a recombinant in the F1 progeny?

yellow-bodied, red-eyed males

Based on the hypothesis that the two genes for eye color and body color obey Mendel's law of independent assortment, calculate the expected values of each of the four phenotypes. (Use the actual and expected data shown to the left)

The expected number of offspring with each phenotype is 551.

A wild type fly is heterozygous for sable eyes, grey body and short bristles. It is crossed to a male fly homozygous for sable, grey and short. The following progeny phenotypes were observed. Sable, grey, short: 400 Wild type: 425 Sable: 60 Grey, short: 62 Sable, short: 22 Grey: 23 Short: 3 Sable, grey: 5 1. What is the order of the genes? 2. What is the distance between sable and short? 3. What is the distance between grey and short?

1. sable, short, grey 2. 13 mu 3. 5.3 mu

What is the map distance between these two genes?

34.5

T/F: 5. Genetic counselors can use genetic maps to determine if an individual will express a particular gene.

False

A scientist is studying body color, elbow roughness, and the finger length of a new alien species. Based on the location of each of these alleles, which statement is true?

The scientist will likely observe more recombinant offspring involving body color and finger length than elbow roughness and finger length.

Which of the following hypotheses is best to determine if the genes that Morgan studied for eye color and body color are linked or if they assort independently?

The two genes for eye color and body color obey Mendel's law of independent assortment.

Refer to the cross done in the interactive exercise on linkage to answer this question. If, when counting the F1 progeny, you did not separate the two nonrecombinant (parental) progeny classes by gender, hypothetically, how many of each nonrecombinant class would then be present in those two groups?

There would be twice as many in each nonrecombinant class grouping.

T/F: 6. Genetic maps provide plant and animal breeders with helpful information for improving agriculturally important strains through selective breeding programs.

True

Using the above graph and your understanding of recombination, which choice best explains why the percentage of recombinant offspring plateaus at 50%?

When two different genes are more than 50 map units apart, they follow the law of independent assortment in a testcross.

Determine the Chi square value for the data using the equation provided in the text.

X2 = 2110

The recombinant gremlins of the F2 generation were produced by crossing over that occurred:

during spermatogenesis in the F1 males.

What genetic phenomenon accounts for the twin spot shown in the fly above?

mitotic recombination

A crossover in meiosis is an exchange of genetic material between _____.

non-sister chromatids of homologous chromosomes

Based on a chi square value of 2110, the hypothesis that the two genes for eye color and body color obey Mendel's law of independent assortment, should be:

rejected

T/F: 1. A genetic map allows geneticists to understand the overall complexity and genetic organization of a particular species.

True

T/F: 2. Knowing the locus of a gene within a genetic map can help molecular geneticists clone the gene.

True

T/F: 3. Genetic maps can be used to improve our understanding of the evolutionary relationships among species.

True

T/F: 4. Genetic maps can be used to diagnose and perhaps someday treat inherited human diseases.

True

Chi square analysis of linkage vs. independent assortment

Chi square analysis is used to examine the similarities between two or more variables. This method can be used to determine if the outcome of a dihybrid cross is consistent with genetic linkage or independent assortment of the chromosomes. Thomas Hunt Morgan investigated the inheritance pattern of different traits that had been shown to follow an X-linked pattern of inheritance. Morgan's experiments, which focused on body and eye color, produced the following offspring: 1159 gray body, red eyes; 1017 yellow body, white eyes; 17 gray body, white eyes; and 12 yellow body, red eyes. However, the laws of segregation and independent assortment predict a 1:1:1:1 ratio among the four phenotypes when a heterozygous female is crossed to a hemizygous male. To conduct a chi square analysis of Morgan's data, we must first propose a hypothesis, which assumes that there is no real difference between the measured values and the predicted values. A typical hypothesis for the chi square is that the differences between the observed and expected results are due only to random chance. Then calculate the expected values of each of the phenotypes based on the hypothesis. The third step is to apply the chi square formula, using the data for the observed values (O) and the expected values (E) that have been calculated in step 2. The calculated chi square value (X2) is compared to chi square values that indicate threshold values. Threshold values are values above which the probability that the calculated chi square value could occur by random chance. If the experimental chi square value is above the tabulated chi square value at the appropriate degrees of freedom and probability then the hypothesis will be rejected.

How did the Creighton and McClintock experiments indicate that recombinant offspring carry chromosomes that are the result of crossing over?

Creighton and McClintock were able to correlate the formation of recombinant offspring with the presence of chromosomes that had exchanged pieces due to crossing over.

T/F: Crossing over allows the reassortment of linked genes.

True

T/F: Crossing over occurs during prophase I of meiosis.

True

A fern plant you are studying can have one of two phenotypes for the surface of its leaves. The leaf surface can be fuzzy or it can be smooth. The phenotype is under the control of a single gene designated as Fz. The dominant phenotype is smooth leaf surfaces, and the recessive is fuzzy leaf surfaces. You are growing a plant that is heterozygous (Fz fz), and you suddenly notice that all the leaves that grow from a new, young branch are fuzzy. You use your knowledge of the fern's biology to determine that the leaves are fuzzy because all their cells have the genotype fz fz. You suspect that mitotic crossing over has occurred as this plant has been growing. An observation that would support your hypothesis would be to find that __________.

the cells of leaves on an adjacent branch are all homozygous dominant