Various sequences for teaching genetics have been proposed. Three seventh-grade biology textbooks in Taiwan share similar key knowledge assemblages but have different knowledge arrangements. To investigate the influence of knowledge arrangements on student understanding of genetics, we compared students’ reading comprehension of the three texts that exhibit different knowledge arrangements. The results revealed that one particular knowledge arrangement (genetic materials, mitotic and meiotic models, genetic model, and molecular model) leads to the greatest reading comprehension of genetics. The differences are found in knowledge of mitotic and meiotic models. The results of this study are valuable for use in organizing instruction.

Understanding the ideas of genetics is crucial for contemporary citizens and is a part of compulsory education in numerous countries because of rapid advancements in genetic research and technology (e.g., National Research Council [NRC], 1996; Taiwan Ministry of Education, 2000). However, extensive educational research has indicated that students encounter many difficulties in learning genetics even after instruction, and these difficulties have been attributed to the inadequacy of current instructional methods and materials (Tolman, 1982; Cho et al., 1985; Banet & Ayuso, 2000; AAAS, 2006; Duncan & Reiser, 2007), the daily life experiences of students (Lewis & Kattmann, 2004; Venville et al., 2005), and the level of cognitive operation and reasoning ability involved (Cavallo, 1996).

Stewart et al. (2005) argued that to truly understand the ideas of genetics, knowledge of three integrated conceptual models is necessary: the genetic model, which is usually referred to as “classical inheritance” and which integrates the knowledge of reproduction, fertilization, and genetic materials; the meiotic model, which regards the processes of meiosis underlying gene recombination and chromosome sorting; and the molecular model, which pertains to mechanisms of gene expression. The domain of genetics encompasses not only numerous material entities across multiple organizational levels (e.g., micromolecules [nucleotides and alleles], macromolecules [chromosomes and proteins], cells, individuals, and even individuals of different generations [parents and offspring]), but also various processes (e.g., reproduction, mitosis, meiosis, fertilization, and gene expression). To comprehend genetic phenomena thoroughly, students must integrate knowledge about the material and process concepts at each organizational level.

Learning progressions have been advocated by the National Assessment of Educational Progress (2006) and the NRC (2005, 2007) as a way to develop coherent learning sequences that cross multiple grades. The intent is to represent potential paths that students can follow to progressively deepen their understanding of complex subjects as they rise through the grades. Duncan et al. (2009) suggested a learning progression for modern genetics that begins in the late elementary grades and continues into high school. Certain researchers have argued that the teaching sequence would flow more effectively from the meiotic model to the genetic model (Tolman, 1982; Williams et al., 2012), whereas others have proposed the reverse sequence (Cho et al., 1985; Banet & Ayuso, 2000). By adding the molecular model, Roseman and colleagues (as cited in Duncan et al., 2009) suggested a teaching sequence in which knowlege of gene-expression mechanisms is introduced before genetic and meiotic models.

Constructivism indicates that the preknowledge of students is a key factor for their follow-up learning. In numerous countries, textbooks are the main instructional materials for presenting key concepts and knowledge to students and can, to a certain extent, reflect the anticipant instructional sequence. Whether conceptual sequences and knowledge arrangements in textbooks influence student understanding of genetics requires further investigation.

In Taiwan, genetics has been introduced in the Reproduction and Inheritance units of the seventh grade for several decades, whereas the molecular model (gene-expression mechanisms) has not been included. Three prevalent biology textbooks (labeled H, K, and N) for this grade, with occupational percentages of ~30% for each, were developed according to the Taiwan curricular standard. They have similar key knowledge assemblages but are compiled differently.

Methods

Texts

We compiled three texts with different knowledge arrangements of the same sentences and figures (labeled I, II, and III; Table 1). The knowledge arrangement of the I text was parallel to those of the K and N textbooks and the teaching sequence proposed by Tolman (1982) and Williams et al. (2012): cells and chromosomes, the mitotic and meiotic models, the genetic model, the molecular model, and chromosomes and genes. The knowledge arrangement of the II text was parallel to that of the H textbook: the reproduction portion of the genetic model, cells and chromosomes, the mitotic and meiotic models, the fertilization portion of the genetic model, the molecular model, and chromosomes and genes. The knowledge arrangement of the III text was mainly based on the teaching sequence suggested by Roseman and colleagues (as cited in Duncan et al., 2009): the genetic materials, the molecular model, the mitotic and meiotic models, and the genetic model.

Table 1.

The knowledge arrangements of three texts (labeled I, II, and III).

IIIIII
Part 1: Cells and chromosomes, and the mitotic and meiotic models. Part 1: The reproduction portion of the genetic model, cells and chromosomes, and the mitotic model. Part 1: The genetic materials. 
Part 2: The genetic model. Part 2: The meiotic model, and the fertilization portion of the genetic model. Part 2: The molecular model. 
Part 3: The molecular model. Part 3: The molecular model. Part 3: The mitotic and meiotic models. 
Part 4: Chromosomes and genes, and examples of the genetic model (ABO blood types and sex chromosomes). Part 4: Chromosomes and genes, and examples of the genetic model (ABO blood types and sex chromosomes). Part 4: The genetic model and examples (ABO blood types and sex chromosomes). 
IIIIII
Part 1: Cells and chromosomes, and the mitotic and meiotic models. Part 1: The reproduction portion of the genetic model, cells and chromosomes, and the mitotic model. Part 1: The genetic materials. 
Part 2: The genetic model. Part 2: The meiotic model, and the fertilization portion of the genetic model. Part 2: The molecular model. 
Part 3: The molecular model. Part 3: The molecular model. Part 3: The mitotic and meiotic models. 
Part 4: Chromosomes and genes, and examples of the genetic model (ABO blood types and sex chromosomes). Part 4: Chromosomes and genes, and examples of the genetic model (ABO blood types and sex chromosomes). Part 4: The genetic model and examples (ABO blood types and sex chromosomes). 

For each text, two experienced (>6 years of teaching) junior high school teachers validated the textual content. To evaluate textual readability, one or two paragraphs from four parts of the texts (~250 words) were selected for assessment by using the Cloze technique (Singer & Donlan, 1980). The percentage of correctly answered words in the 128 blanks in the four parts read by 165 sixth-grade students was 81.8%, indicating that the students could read these texts by themselves.

Study Context

The study was conducted at a public junior high school in Taipei County. Students were randomly assigned to classes. Seventh-grade students (aged 13–14) from eight classes who had not yet studied the Reproduction and Inheritance units participated in the study. The texts were divided into four parts, and the students read one part of the text and finished the associated questions during one period every week.

In order to help students learn the essential knowledge and become familiar with the assessment style, the associated questions at the end of the four parts were designed to prompt students to review the essential knowledge and find the answers in the text. Answer keys were provided at the end of each period for review. The students’ answers to the associated questions were not collected for analysis.

After 4 weeks, the students reviewed the entire text and wrote an assessment for analysis during another period. A total of 40, 59, and 70 students, from two, three, and three classes, completed the entire study with the I, II, or III text, respectively.

Written Assessment

We administered a written assessment designed to elicit student understanding of the genetic phenomena. The assessment was composed of 17 multiple-choice items and 11 true/false themes (one of which had four items; a theme is illustrated in  Appendix 1). These 61 items ( Appendix 2) could be divided into four categories (genetic materials, mitotic and meiotic models, genetic model, and molecular model). Because the molecular model (gene expression mechanisms) was not included in the curricular standard, there was only one item regarding this model. The assessment items were also validated by the six junior high school teachers. Cronbach’s α = 0.801 for the assessment of 60 seventh-grade students from two classes who learned the Reproduction and Inheritance units.

Data Analysis

We used analysis of covariance (ANCOVA; significance level P < 0.05) to compare the assessment scores for the three texts and used the biology scores from the previous grade’s exam (M = 66.04, SD = 20.583) as the covariate, using SPSS software. The correlation coefficient between previous-grade exam scores and written assessment scores was 0.456, which is significant at the 0.01 level, and there was no significant interaction effect between texts and previous-grade exam scores (F = 2.710, df = 2 and 163, P = 0.070).

Results

Table 2 summarizes the ANCOVA results of all items and categories. The written assessment scores of students who read the I text (MI = 31.195) were significantly higher than those of students who read the II (MII = 28.773) and III (MIII = 27.694) texts (F = 6.435, df = 2 and 165, P = 0.002).

Table 2.

Summary of the ANCOVA results. Categories: (A) the genetic materials, (B) mitotic and meiotic models, (C) the genetic model, and (D) the molecular model. Significance: *P < 0.05.

TextEstimated Marginal Means (SE)FSignificancePartial Eta SquaredPairwise Comparisons
II III 
Total 31.195 (0.776) 28.773 (0.631) 27.694 (0.582) 6.435 0.002* 0.072 I > II = III 
Category A 10.219 (0.328) 9.428 (0.267) 9.342 (0.246) 2.494 0.086 0.029 I > III, I = II, II = III 
Category B 8.186 (0.385) 7.623 (0.313) 6.740 (0.289) 4.886 0.009* 0.056 I = II > III 
Category C 12.024 (0.403) 11.022 (0.327) 10.810 (0.302) 3.018 0.052 0.035 I > III, I = II, II = III 
Category D 0.766 (0.067) 0.699 (0.055) 0.801 (0.050) 0.965 0.383 0.012 I = II = III 
TextEstimated Marginal Means (SE)FSignificancePartial Eta SquaredPairwise Comparisons
II III 
Total 31.195 (0.776) 28.773 (0.631) 27.694 (0.582) 6.435 0.002* 0.072 I > II = III 
Category A 10.219 (0.328) 9.428 (0.267) 9.342 (0.246) 2.494 0.086 0.029 I > III, I = II, II = III 
Category B 8.186 (0.385) 7.623 (0.313) 6.740 (0.289) 4.886 0.009* 0.056 I = II > III 
Category C 12.024 (0.403) 11.022 (0.327) 10.810 (0.302) 3.018 0.052 0.035 I > III, I = II, II = III 
Category D 0.766 (0.067) 0.699 (0.055) 0.801 (0.050) 0.965 0.383 0.012 I = II = III 

We considered the following four categories to determine significant differences: (A) the genetic materials, (B) the mitotic and meiotic models, (C) the genetic model, and (D) the molecular model. The differences in total scores are mainly in category B. The category B scores of students who read the I text (MIB = 8.186) or the II text (MIIB = 7.623) were significantly higher than those of students who read the III text (MIIIB = 6.740) (F = 4.886, df = 2 and 165, P = 0.009). Also, there were slight differences between category A (P = 0.086) and category C (P = 0.052). In category D, no significant difference was found among the scores of the three groups of students (P = 0.383).

Discussion & Implications

Our results revealed that the students who read the I text had a clearer understanding of the genetics than those who read the II and III texts. This result supports the teaching sequence suggested by Tolman (1982) and Williams et al. (2012), rather than those proposed by Banet and Ayuso (2000), Cho et al. (1985), and Roseman (as cited in Duncan et al., 2009).

The results for the four categories showed that the significant differences were in category B, and that slight differences existed in categories A and C. The results indicated that the III text was less helpful to students for constructing the mitotic and meiotic models, and that the arrangements of the II and III texts might retard understanding of the genetic model and genetic materials. Moreover, rather than the estimated marginal means in the other three categories, only those in category B were below average for all three groups of students (I, II, and III texts). This implies that the mitotic and meiotic models are more difficult than the other knowledge for most students to comprehend.

In the I text, the material concepts at adjacent levels (e.g., cell and chromosome) were connected and accompanied by corresponding process concepts (e.g., mitosis). However, in the II text, the material concepts at distinct levels were accompanied by corresponding process concepts and connected occasionally with adjacent material concepts. The II text may imply too few connections between levels for students to integrate. In the III text, the material concepts at all levels (individual, cell, chromosome, and gene) were introduced first and followed by distinct process concepts. The III text may have overwhelmed students with too many levels at the beginning. When arranging the knowledge in textbooks or instruction, we could use the I text, which scaffolds student knowlege by integrating two adjacent material concepts (cell and chromosome) initially and then adds other adjacent concepts one-by-one (individual and then gene) for understanding the involvement of material concepts in mitosis, meiosis, or gene-expression processes, and for further understanding genetic processes across multiple levels.

The results of this study rely on the reading comprehension of students. The students in our study learned the assigned genetics knowledge by themselves, without the instruction of teachers; they had lower mean scores on the assessment than students who received teacher instruction. The results reflect the actual achievements and difficulties of students who initially encounter genetics learning, and they are worthy of consideration for use in instruction. Although the knowledge arrangements of texts influence the reading comprehension of students, it is necessary to examine whether the influence on understanding is reduced under instruction that involves substantial scaffolding by teachers.

Acknowledgment

This research was supported by the National Science Council, Taiwan, ROC (grant no. NSC 99-2511-S-003-016-MY2).

References

References
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Appendix 1. An example of the true/false theme with 4 items.

Theme: Regarding the 23rd pair of human chromosomes.

T2-1. Each chromosome consists of many DNA molecules and proteins.

T2-2. Epithelial cells contain the 23rd pair of human chromosomes.

T2-3. The X chromosome of a male is inherited from his mother.

T2-4. There is one Y chromosome in every sperm cell.

Appendix 2. The categories and ideas of assessment items. Categories: (A) the genetics materials, (B) mitotic and meiotic models, (C) genetic model, and (D) molecular model. The multiple-choice items are numbered, and the true/false themes (one of which has 4 items) are numbered and denoted by “T.”

(A) The Genetic Materials (total 18 items) 
 A chromosome consists of a DNA molecule and proteins T2-1 
 Genes are located within cell T3-1 
 Paired chromosomes that have similar length and shape are called “homologous” chromosomes T4-3 
 Diploid cells have pairs of chromosomes 
 Somatic cells have the same sets of chromosomes 
 Somatic cells have two sets of chromosomes T2-2 
 The gene at a specific locus determines a certain trait T4-1 
 There are many gene loci within a chromosome T1-1 
 The gene organization of each kind of chromosomes is distinct 11, T5-4 
 Somatic cells contain the entire genome T5-1, T11-4 
 Somatic cells contain the same genome T5-2 
 The alleles are located within a specific pair of chromosomes 
 The alleles are located at the equivalent gene loci of homologous chromosomes 14, T4-2 
 There are three alleles for the ABO blood type T5-3 
 The homologous chromosomes have the same organization  T3-3 
(B) The Mitotic & Meiotic Models (total 19 items) 
 Mitosis enables a multicellular organism to grow and develop T7-3 
 The daughter cells from mitosis have pairs of chromosomes T7-1 
 The daughter cells from mitosis have two sets of chromosomes T7-2 
 During mitosis, each chromosome (along with alleles) replicates once 15, 17 
 The daughter cells from mitosis have the same number of chromosomes as the original cell has 12 
 The daughter cells from mitosis have the same alleles as the original cell has T3-2, T7-4 
 The homologous duplicated chromosomes are pulled apart 16 
 The gametes have unpaired chromosomes 2, T1-2 
 The gametes have half the number of chromosomes as the original cell has 13 
 Half of the sperm cells contain an X chromosome and half contain a Y chromosome along with its haploid set of autosomes T2-4 
 Allele pairs separate from each other during the production of gametes 3, T6-4, T10-1 
 The gametes have unpaired alleles 4, T11-2 
 The gametes have one allele of entire genes 
(C) The Genetic Model (total 23 items) 
 The zygotes have two sets of chromosomes T1-3 
 Monogenic inheritance is where a single gene affects one trait T6-1 
 Polygenic inheritance is an additive effect of two or more genes on a single trait T10-4 
 Half of the chromosomes are inherited from the organism’s male parent 
 The offspring from sexual reproduction have the same number of chromosomes as parents have T1-4 
 One homologous chromosome is inherited from the organism’s male parent, and the other from its female parent T4-4 
 The gametes contribute alleles to offspring 10 
 The gametes fertilize randomly and contribute alleles to offspring T10-2 
 Organisms in which the two alleles are different have the dominant characteristic T10-3, T11-1 
 A boy will be born if the egg is fertilized by Y-bearing sperm T2-3 
 The offspring from sexual reproduction might have the same genotype as parents have T3-4, T11-3 
 Some phenotypes of the offspring from sexual reproduction may be different from those of their parents T6-3, T8-1 
 The siblings from sexual reproduction have diverse phenotypes 8, T8-2 
 The offspring from asexual reproduction have the same phenotypes as parents have T8-3 
 The siblings from asexual reproduction have the same phenotypes T8-4 
 The offspring from asexual reproduction have the same chromosomes as parents have T9-1 
 The siblings from asexual reproduction have the same chromosomes T9-2, T9-3 
 The offspring from asexual reproduction have the same genotypes as parents have T9-4 
(D) The Molecular Model (total 1 item) 
 Genes determine heritable traits by gene expression T6-2 
(A) The Genetic Materials (total 18 items) 
 A chromosome consists of a DNA molecule and proteins T2-1 
 Genes are located within cell T3-1 
 Paired chromosomes that have similar length and shape are called “homologous” chromosomes T4-3 
 Diploid cells have pairs of chromosomes 
 Somatic cells have the same sets of chromosomes 
 Somatic cells have two sets of chromosomes T2-2 
 The gene at a specific locus determines a certain trait T4-1 
 There are many gene loci within a chromosome T1-1 
 The gene organization of each kind of chromosomes is distinct 11, T5-4 
 Somatic cells contain the entire genome T5-1, T11-4 
 Somatic cells contain the same genome T5-2 
 The alleles are located within a specific pair of chromosomes 
 The alleles are located at the equivalent gene loci of homologous chromosomes 14, T4-2 
 There are three alleles for the ABO blood type T5-3 
 The homologous chromosomes have the same organization  T3-3 
(B) The Mitotic & Meiotic Models (total 19 items) 
 Mitosis enables a multicellular organism to grow and develop T7-3 
 The daughter cells from mitosis have pairs of chromosomes T7-1 
 The daughter cells from mitosis have two sets of chromosomes T7-2 
 During mitosis, each chromosome (along with alleles) replicates once 15, 17 
 The daughter cells from mitosis have the same number of chromosomes as the original cell has 12 
 The daughter cells from mitosis have the same alleles as the original cell has T3-2, T7-4 
 The homologous duplicated chromosomes are pulled apart 16 
 The gametes have unpaired chromosomes 2, T1-2 
 The gametes have half the number of chromosomes as the original cell has 13 
 Half of the sperm cells contain an X chromosome and half contain a Y chromosome along with its haploid set of autosomes T2-4 
 Allele pairs separate from each other during the production of gametes 3, T6-4, T10-1 
 The gametes have unpaired alleles 4, T11-2 
 The gametes have one allele of entire genes 
(C) The Genetic Model (total 23 items) 
 The zygotes have two sets of chromosomes T1-3 
 Monogenic inheritance is where a single gene affects one trait T6-1 
 Polygenic inheritance is an additive effect of two or more genes on a single trait T10-4 
 Half of the chromosomes are inherited from the organism’s male parent 
 The offspring from sexual reproduction have the same number of chromosomes as parents have T1-4 
 One homologous chromosome is inherited from the organism’s male parent, and the other from its female parent T4-4 
 The gametes contribute alleles to offspring 10 
 The gametes fertilize randomly and contribute alleles to offspring T10-2 
 Organisms in which the two alleles are different have the dominant characteristic T10-3, T11-1 
 A boy will be born if the egg is fertilized by Y-bearing sperm T2-3 
 The offspring from sexual reproduction might have the same genotype as parents have T3-4, T11-3 
 Some phenotypes of the offspring from sexual reproduction may be different from those of their parents T6-3, T8-1 
 The siblings from sexual reproduction have diverse phenotypes 8, T8-2 
 The offspring from asexual reproduction have the same phenotypes as parents have T8-3 
 The siblings from asexual reproduction have the same phenotypes T8-4 
 The offspring from asexual reproduction have the same chromosomes as parents have T9-1 
 The siblings from asexual reproduction have the same chromosomes T9-2, T9-3 
 The offspring from asexual reproduction have the same genotypes as parents have T9-4 
(D) The Molecular Model (total 1 item) 
 Genes determine heritable traits by gene expression T6-2