9.4.3.2 Variation within Species

Correlations

• NSES Standardsp. 185
  • Transmission of genetic information to offspring occurs through egg and sperm cells that contain only one representative from each chromosome pair.  An egg and a sperm unite to form a new individual.  The fact that the human body is formed from cells that contain two copies of each chromosome - and therefore two copies of each gene - explains many features of human heredity, such as how variations that are hidden in one generation can be expressed in the next.
• AAAS Atlas: Vol. 1, pp. 69 and 71 (see benchmarks below).
• Benchmarks of Science Literacypg 108. The information passed from parents to offspring is coded in DNA molecules.
  • The sorting and recombination of genes in sexual reproduction results in a great variety of possible gene combinations from the offspring of any two parents.  5b/2
  • Some new gene combinations make little difference, some can produce organisms with new and perhaps enhanced capabilities, and some can be deleterious.
  • Genes are segments of DNA molecules.  Inserting, deleting, or substituting DNA segments can alter genes.  An altered gene may be passed on to every cell that develops from it.  The resulting features may help, harm, or have little or no effect on the offspring's success in its environment.  5b/4
  • Gene mutations can be caused by such things as radiation and chemicals.  When they occur in sex cells, the mutations can be passed on to offspring; if they occur in other cells, they can be passed on to descendant cells only.  The experiences an organism has during its lifetime can affect its offspring only if the genes in its own sex cells are changed by the experience.  5b/5

Framework for K-12 Science Education

The information passed from parents  to offspring  is coded  in the DNA molecules that  form the chromosomes. In sexual reproduction,  chromosomes can sometimes  swap  sections during  the process of meiosis (cell division),  thereby  creating  new genetic combinations and thus  more  genetic variation. Although  DNA replication  is tightly regulated  and remarkably accurate,  errors  do occur and result in mutations, which are also a source of genetic variation. Environmental factors  can also cause mutations in genes, and viable mutations are inherited. Environmental factors  also affect expression  of traits, and hence affect the probability of occurrences  of traits  in a population. Thus the variation and distribution of traits  observed  depend  on both  genetic and environmental factors. 12LS3.B

In multicellular organisms  individual  cells grow and then divide via a process called mitosis, thereby  allowing  the organism  to grow. The organism  begins as a single cell (fertilized egg) that  divides successively to produce many cells, with each parent  cell passing identical  genetic material  (two variants of each chromosome pair) to both  daughter cells. As successive subdivisions  of an embryo’s cells occur,  programmed genetic instructions and small differences in their immediate  environments activate  or inactivate  different  genes, which cause the cells to develop differently—a  process called differentiation. Cellular division and differentiation produce  and maintain a complex  organism,  composed of systems of tissues and organs  that  work  together  to meet the needs of the whole organism.  In sexual reproduction, a specialized type of cell division called meiosis occurs that  results in the production of sex cells, such as gametes in animals  (sperm and eggs), which contain  only one member  from each chromosome  pair in the parent  cell. 12LS1.B

Common Core Standards

Common Core Standards (i.e. connections with Math, Social Studies or Language Arts Standards):

Math standards can be easily incorporated into this topic.

Math  9.3.1.5  Make reasonable estimates and judgments about the accuracy of values resulting from calculations involving measurements.

Students may make predictions as to the outcome of the diversity resulting from independent assortment and segregation.

Math 9.4.2.3  Design simple experiments and explain the impact of sampling methods, bias, and the phrasing of questions asked during data collection.

This standard can be addressed with all data collection methods.  Statistical analysis and graphing can be done.

Common Core Language Arts:  Students can write a laboratory report in the proper form, using their knowledge of technical writing skills.  Common core standards addressed:

RST.9-10.1.  Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.

RST.9-10.2.  Determine the central ideas or conclusions of a text; trace the text's explanation or depiction of a complex process, phenomenon, or concept; provide an accurate summary of the text.

RST.9-10.3.  Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.