Formative Assessment Probe
Assessment Life Science Middle School
This is the new updated edition of the first book in the bestselling Uncovering Student Ideas in Science series. Like the first edition of volume 1, this book helps pinpoint what your students know (or think they know) so you can monitor their learning and adjust your teaching accordingly. Loaded with classroom-friendly features you can use immediately, the book includes 25 “probes”—brief, easily administered formative assessments designed to understand your students’ thinking about 60 core science concepts.
The purpose of this assessment probe is to elicit students’ ideas about heredity. The probe is designed to reveal how students think organisms inherit observable traits.
Inherited traits, genes, sexual reproduction
The best response is Alexa’s: The baby mice got half their inherited information from their father and half from their mother. The first step in the production of offspring from the two mice is fertilization of the female’s egg by the male’s sperm. Egg and sperm each contain half the number of mouse chromosomes. Genes are found on chromosomes. A gene is a segment of DNA on a chromosome that carries instructions for a particular trait, such as fur color. During fertilization, matched pairs of chromosomes (half from the mother and half from the father) come together, and a single cell results (which will divide and eventually become the baby mouse). The baby mouse contains a full set of chromosomes—with half the genes on their chromosomes coming from the mother and half from the father. The combination that results determines the offspring’s traits.
One way in which genes are expressed was described by Gregor Mendel, who believed that traits could be either dominant or recessive. When two genes for the same trait are paired and one of the genes is dominant, the dominant gene will be expressed. In applying Mendelian genetics to the example of the mouse fur color (a simplified way of looking at coat color), black fur color would be dominant. Even if the offspring had only one gene for black fur, the trait that would be expressed is black fur. White fur would be a recessive trait that is expressed when a dominant gene is not present. The white offspring would have two genes for white fur color. Mendelian genetics is a simplified first step in understanding how genes are expressed, but understanding genetics is much more complex, and the expression of a trait such as fur color in mice involves multiple genes. The key idea in this probe is that an organism’s inherited traits are determined by the pairing of genes from the mother and father, with each parent contributing 50% of the genes. The combination of genes determines which traits are expressed. It is not the result of one sex having more or stronger traits (or genes) as described in Jerome’s and June’s responses.
Black and white mice have the same number of genes (contrary to Seif’s response); they are just expressed differently. Coat color in mice is not determined by sex, as described in Fiona’s response. For example, some of the white mice could be male if they received a recessive gene from both the mother and father.
Lydia’s response is a teleological argument that implies that some intentional force of nature directs the traits that offspring will exhibit, rather than traits being the result of gene expression. However, the expression of some traits can be affected by the environment. Billy’s response is similar to historical beliefs. Before Mendel, many people thought traits were passed on through the blood.
In the primary grades, students are beginning to learn about inherited characteristics. They explore traits at the organism level. They develop a theory of “kinship” by observing that offspring are similar to their parents yet do not always look exactly like their parents or each other. In the later elementary grades, they begin to develop an understanding that traits are passed on from parents to offspring and that offspring can look or function differently because they have different inherited information. They can discuss how a mixedbreed puppy looks different from its parents yet has some similar characteristics of each parent. This phenomenon should be explored with a variety of organisms. However, it is too early to introduce the genetic mechanism of inheritance. By eliminating some of the distracters, this probe can be used to examine students’ early ideas about how traits are passed on to offspring before they encounter concepts such as genes, chromosomes, DNA, and proteins.
Middle School Students
In middle school, students learn core ideas about the mechanism of inheritance, combining ideas about reproduction, cell division, and basic genetics. The focus at this level is on cellular mechanisms. They develop an understanding of the role of chromosomes, genes, alleles, and proteins in passing on characteristics from one generation to the next, including the idea that genes control proteins, which can affect how a trait is expressed. At this grade level, it is important that students understand that half of their genes come from their mother and half from their father and that this random combination results in the inherited traits they may exhibit. Students should recognize the role of chance in determining which chromosomal pairs come together during fertilization and that probability can help predict the outcome of some inherited characteristics. Students may start with basic Mendelian genetics; however, it is important for them to know that not all traits are the result of the pairing of a single gene type. A more detailed mechanism of genetics can wait until high school.
High School Students
In high school, the link between genetic information and expression of traits is further developed and deepened. Students learn more complex details of the mechanism of inheritance and how various gene combinations code for proteins and that the structure and function of proteins results in the expression of traits. They should be able to explain why some traits are expressed and some are not. They can now delve into genetics at a molecular level. However, they are not expected to know the specific steps in transcription and translation of genes to proteins.
This probe can be used with students in grades 5–12. If students have a conceptual understanding of genes, consider substituting the words traits and inherited information with the word genes.
LS3.B: Variation of Traits
In sexually reproducing organisms, each parent contributes half of the genes acquired (at random) by the offspring. Individuals have two of each chromosome and hence two alleles of each gene, one acquired from each parent. These versions may be identical or may differ from each other.
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