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Table 1.

Coding criteria used in the content analysis of undergraduate biology textbooks.

CategoryConcept StatementCriteria Used in Coding
Homology Maternal and paternal chromosomes of the same kind are homologous. Color is used to differentiate maternal and paternal chromosomes in a homologous pair and/or each chromosome in the pair is labeled “maternal” or “paternal.” 
Homologous chromosomes are different from sister chromatids. A figure contains a pair of replicated, homologous chromosomes (which are explicitly described as such) with sister chromatids clearly labeled. 
X and Y chromosomes behave as a homologous pair. The X and Y chromosomes appear together as a homologous pair. 
Ploidy Chromosomes may contain one or two DNA molecules,a depending on whether or not DNA replication has taken place. Condensed chromosomes appear as one-DNA molecules before DNA replication and as two-DNA molecules (sister chromatids) after replication. Figure legend or labels indicate that both forms are chromosomes. 
Chromosomes rather than chromatids determine ploidy. Diploid cells are drawn with two sets of chromosomes (which is pointed out in figure labels and/or figure legend) while the haploid version has only one set of chromosomes, clearly indicated. 
Gametes are haploid. A gamete is clearly labeled as haploid. 
A cell becomes haploid after meiosis I. A cell is clearly labeled as haploid after meiosis I but before meiosis II. 
Segregation Physical linkage is essential for proper chromosome segregation. Replicated homologous chromosomes are paired (and appear to be physically touching) before they are shown aligned at the metaphase plate. 
DNA sequence homology determines pairing. Homologous chromosomes are drawn paired and the identical DNA sequence on both chromosomes is clearly shown. 
Crossing over requires DNA sequence homology. A close-up look at a Holliday junction intermediate is shown, with identical DNA sequence on both strands clearly shown. 
CategoryConcept StatementCriteria Used in Coding
Homology Maternal and paternal chromosomes of the same kind are homologous. Color is used to differentiate maternal and paternal chromosomes in a homologous pair and/or each chromosome in the pair is labeled “maternal” or “paternal.” 
Homologous chromosomes are different from sister chromatids. A figure contains a pair of replicated, homologous chromosomes (which are explicitly described as such) with sister chromatids clearly labeled. 
X and Y chromosomes behave as a homologous pair. The X and Y chromosomes appear together as a homologous pair. 
Ploidy Chromosomes may contain one or two DNA molecules,a depending on whether or not DNA replication has taken place. Condensed chromosomes appear as one-DNA molecules before DNA replication and as two-DNA molecules (sister chromatids) after replication. Figure legend or labels indicate that both forms are chromosomes. 
Chromosomes rather than chromatids determine ploidy. Diploid cells are drawn with two sets of chromosomes (which is pointed out in figure labels and/or figure legend) while the haploid version has only one set of chromosomes, clearly indicated. 
Gametes are haploid. A gamete is clearly labeled as haploid. 
A cell becomes haploid after meiosis I. A cell is clearly labeled as haploid after meiosis I but before meiosis II. 
Segregation Physical linkage is essential for proper chromosome segregation. Replicated homologous chromosomes are paired (and appear to be physically touching) before they are shown aligned at the metaphase plate. 
DNA sequence homology determines pairing. Homologous chromosomes are drawn paired and the identical DNA sequence on both chromosomes is clearly shown. 
Crossing over requires DNA sequence homology. A close-up look at a Holliday junction intermediate is shown, with identical DNA sequence on both strands clearly shown. 
a

Reworded from original statement, which said: “Chromosomes may contain one or two chromatids….”

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