Statistical Tests and Data Analysis · with figure
A cross is expected to produce a 1:1 phenotype ratio. The observed counts are shown. What is the chi-square value?
- A0.32; an incorrect unsquared-deviation setup
- B16.00; the raw count difference
- C1.28; only one phenotype category included
- D2.56; both phenotype contributions summedcorrect
Why D is correct
For 100 offspring in a 1:1 ratio, expected counts are 50 and 50. Chi-square = (42-50)^2/50 + (58-50)^2/50 = 64/50 + 64/50 = 2.56.
The stem asks for a numerical or quantitative judgment: "A cross is expected to produce a 1:1 phenotype ratio. The observed counts are shown. What is the chi-square value". The safe route is to identify the counted event, use the full denominator, and then interpret the number biologically. Here the worked reasoning is For 100 offspring in a 1:1 ratio, expected counts are 50 and 50, so choices based on 0.32; an incorrect unsquared-deviation setup or 16.00; the raw count difference lose the required setup.
Concept Explanation
Two genes are located very close together on the same chromosome. In the absence of crossing over between them, how are their alleles likely to be inherited?
- APhysical proximity on the same chromosome makes alleles tend to travel togethercorrect
- BThey disappear from gametes because linked genes cannot enter meiosis.
- CThey become RNA bases before gamete formation.
- DThey must be inherited independently because all genes are on different chromosomes.
Why A is correct
Genes that are physically close on the same chromosome are linked and tend to be inherited together unless crossing over separates them.
The stem asks students to explain a specific mechanism, not just recall a unit term: "Two genes are located very close together on the same chromosome. In the absence of crossing over between them,...". The correct choice is supported by Genes that are physically close on the same chromosome are linked and tend to be inherited together unless crossing over separates them. The tempting alternatives such as They disappear from gametes because linked genes cannot enter meiosis or They become RNA bases before gamete formation fail because they do not produce the same outcome described in the stem.
Representing and Describing Data · with figure
A reptile species has embryos with similar genotypes incubated at different temperatures. Which claim is best supported by the data? Use Figure 1 to answer the question.
- AThe lower-temperature group has the higher percentage of phenotype F.
- BEnvironmental temperature is associated with different phenotype distributions.correct
- CTemperature has no association with the phenotype distribution.
- DOnly DNA sequence differences can influence phenotype in any organism.
Why B is correct
The two incubation temperatures are associated with different phenotype distributions. The lower temperature has a higher percentage of phenotype M, while the higher temperature has a higher percentage of phenotype F.
The evidence in the prompt matters before the topic label: "A reptile species has embryos with similar genotypes incubated at different temperatures. Which claim is best...". The supported answer is "Environmental temperature is associated with different phenotype distributions" because The two incubation temperatures are associated with different phenotype distributions. Distractors such as lower-temperature group has the higher percentage of phenotype F or Temperature has no association with the phenotype distribution either ignore the stated pattern or name a related concept without matching the evidence.