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The goodness of fit is measured by\({\chi ^{^2}}\). This statistic measures the amounts by which the observed values differ from their respective predictions to indicate how closely the two sets of values match. The formula for calculating this value is

\({\chi ^{}} = \sum \frac{{{{\left( {o - e} \right)}^2}}}{e}\)

Where o=observed and e= expected. Calculate the\({\chi ^{^2}}\)value for the data using the table below. Fill out the table, carrying out the operations indicated in the top row. Then add up the entries in the last column to find the\({\chi ^{^2}}\)value.

Testcross Offspring

Expected

(e)

Observed

(o)

Deviation

(o-e)

(o-e)2

(o-e)2/e

(A-B-)

220

(aaB-)

210

(A-bb)

231

(aabb)

239

\({\chi ^2}\) =sum

Short Answer

Expert verified

The expected number of offspring is estimated at 225. The deviation values are calculated as -5,-15, 4,16. The value of (o-e)2 is calculated as 25, 225, 36, 196. The value of (o-e)2/e is calculated as 0.11,1, .16, and .87 , respectively. The sum is estimated as 2.14.

Step by step solution

01

Goodness of fit

The goodness of fit test is the statistical method that helps determine the accuracy between the expected and observed data.The deviations between these two data sets are easily predicted from this test. It is used to determine the accuracy of the genetic crosses between two different parents and their possible outcomes.

02

Calculation of \({\chi ^{^2}}\)value

The expected values of the unlinked genes are calculated as follows:

Expected number\( = \frac{{tota\ln umber}}{{no.of.offsprings}} = \frac{{900}}{4} = 225\)

The deviation value is calculated as follows:

\(o - e = 220 - 225 = - 5\)

\(o - e = 210 - 225 = - 15\)

\(o - e = 231 - 225 = 6\)

\(o - e = 239 - 225 = 14\)

The value of (o-e)2is estimated as follows:

\(\begin{aligned}{l}{\left( {{\bf{o}} - {\bf{e}}} \right)^{\bf{2}}} = {( - 5)^2} = 25\\{\left( {{\bf{o}} - {\bf{e}}} \right)^{\bf{2}}} = {( - 15)^2} = 225\\{\left( {{\bf{o}} - {\bf{e}}} \right)^{\bf{2}}} = {(6)^2} = 36\\{\left( {{\bf{o}} - {\bf{e}}} \right)^{\bf{2}}} = {(14)^2} = 196\end{aligned}\)

The value of (o-e)2/e is estimated as follows:

\(\begin{aligned}{l}\frac{{\begin{aligned}{*{20}{l}}{{{\left( {{\bf{o}} - {\bf{e}}} \right)}^{\bf{2}}}}\end{aligned}}}{e} = \frac{{25}}{{225}} = 0.11\\\frac{{\begin{aligned}{*{20}{l}}{{{\left( {{\bf{o}} - {\bf{e}}} \right)}^{\bf{2}}}}\end{aligned}}}{e} = \frac{{225}}{{225}} = 1\\\frac{{\begin{aligned}{*{20}{l}}{{{\left( {{\bf{o}} - {\bf{e}}} \right)}^{\bf{2}}}}\end{aligned}}}{e} = \frac{{36}}{{225}} = 0.16\\\frac{{\begin{aligned}{*{20}{l}}{{{\left( {{\bf{o}} - {\bf{e}}} \right)}^{\bf{2}}}}\end{aligned}}}{e} = \frac{{196}}{{225}} = 0.87\end{aligned}\)

The\({\chi ^2}\)is estimated as follows:

\({\chi ^2} = 0.11 + 1 + 0.16 + 0.87 = 2.14\)

The\({\chi ^2}\)is calculated by adding up all the estimated values in the last column and predicted as 2.14.

03

Tabulation with the expected number results

The values are calculated above and listed in the table by the given conditions.

Testcross Offspring

Expected

(e)

Observed

(o)

Deviation

(o-e)

(o-e)2

(o-e)2/e

(A-B-)

225

220

-5

25

0.11

(aaB-)

225

210

-15

225

1

(A-bb)

225

231

6

36

0.16

(aabb)

225

239

14

196

0.87

\({\chi ^2}\) =

2.14

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Most popular questions from this chapter

The ABO blood type locus has been mapped on chromosome 9. A father with type AB blood and a mother who has type O blood have a child with trisomy nine and type A blood. Using this information, can you tell in which parent the non-disjunction occurred? Explain your answer. (See Figures 14.11 and 15.13).

Assume you are mapping genes A, B, C, and D in Drosophila. You know that these genes are linked on the same chromosome, and you determine the recombination frequencies between each pair of genes to be as follows: A-B, 8%; A-C, 28%; A-D, 25%; B-C, 20%; B-D, 33%.

  1. Describe how you determined the recombination frequency for each pair of genes.

  2. Draw a chromosome map based on your data.

The\({\chi ^2}\)value means nothing on its own- it is used to find the probability that, assuming the hypothesis is true, the observed data set could have resulted from random fluctuations. A low probability suggests that the observed data are consistent with the hypothesis, and thus the hypothesis should be rejected, A standard cutoff point used by biologists is a probability of 0.05(5%). If the probability corresponding to the\({\chi ^2}\)value is 0.05or considered statistically significant, the hypothesis (that the genes are unlinked) should be rejected. If the probability is above 0.05, the results are not statistically significant: the observed data are consistent with the hypothesis.

To find the probability, locate your\({\chi ^2}\)value in the\({\chi ^2}\)Distribution table in Appendix F. The 鈥渄egree of freedom鈥 (pdf) of your data set is the number of categories (here,4 phenotypes), minus 1, so df=3.

(a). Determines which values on the df =3 line of the table your calculated\({\chi ^2}\)value lies between.

(b). The column headings for these values show the probability range for your\({\chi ^2}\)number. Based on whether there is non-significant (p\( \le \)0.05) or significant (p>0.05) difference between the observed and expected values, are the data consistent with the hypothesis that the two genes are unlinked and assorting independently, or is there enough evidence to reject this hypothesis?

Reciprocal cross between two primrose varieties, A and B, produced the following results: AfemaleBmaleoffspringwith all green (non-variegated) leaves;BfemaleAmaleoffspring with patterned (variegated) leaves. Explain these results

A planet is inhabited by creatures that reproduce with the same hereditary patterns seen in humans. Three phenotypic characters are height (T = tall, t= dwarf), head appendages (A = antennae, a = no antennae), and nose morphology (S = upturned snout, s = downturned snout). Since the creatures are not 鈥渋ntelligent,鈥 Earth scientists are able to do some controlled breeding experiments using various heterozygotes in testcrosses. For tall heterozygotes with antennae, the offspring are tall antennae, 46; dwarf antennae, 7; dwarf no antennae, 42; tall no antennae, 5. For heterozygotes with antennae and an upturned snout, the offspring are antennae upturned snout 47; antennae downturned snout, 2; no antennae downturned snout, 48; no antennae upturned snout, 3. Calculate the recombination frequencies for both experiments.

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