Module 7
1. Module 7
1.24. Page 4
Module 7—Molecular Genetics: DNA, RNA, and Protein Synthesis
Read
Evolutionary Relationships Between Species
To study how different birds were related in the 1960s, biologists would have looked at their anatomical similarities and differences. For example, they would have compared bone shape, size, and function.
Today DNA is used. Researchers know that the DNA of chimpanzees is 98% the same as human DNA, and the genetic similarity between two humans is more than 99.99%. This knowledge can be used to create a phylogenetic tree that shows the evolutionary relationships between species. Today scientists can compare the DNA of ancient plants, animals, and even bacteria with the DNA of modern organisms in order to look at the ancestry of modern organisms, the movement of populations through time, the evolution of particular disease causing bacteria, and the way that ecosystems respond to climate change.
Ancestry Within a Species
mitochondrial DNA (mtDNA): DNA within the mitochondria; is genetically identical to that of the female parent because the cytoplasm of offspring is derived from the egg (ovum)
chloroplast DNA (cpDNA): circular molecules of DNA found in the chloroplasts of plants; codes for the function of photosynthesis
endosymbiont theory: theory that eukaryotic cells developed by one species of prokaryote engulf another so that organelles are formed
There are other types of DNA used by scientists to study ancestry: mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA). Mitochondrial and chloroplast DNA have their own DNA that is replicated, transcribed, and translated independently from the DNA in the nucleus of the cell. The theory for how these organelles became part of the cell is called the endosymbiont theory.
Typically, when fertilization occurs, the nuclear DNA of the zygote will be a combination of the two parents’ nuclear DNA. When the zygote forms, the cytoplasm and all of the cytoplasmic organelles are donated by the ovum (egg). This means that the mitochondrial DNA will be identical to the mtDNA of the mother.
Through the generations in a family tree, many men and women contribute to the nuclear DNA makeup of an individual, but only one woman contributed to the mtDNA. Your mtDNA is a copy of your mother’s, which is copied from her mother, and so on. Mutations will still occur in mtDNA over time and this mutation rate can help scientists deduce ancestry. The more similar the mtDNA between people, the closer the people are related. The more dissimilar the mtDNA, the more mutations that must have occurred, indicating more time on the evolutionary path must have elapsed or that they are not related.
Read from “Mutations and Genetic Variation” on page 645 to the end of “Genetic Variation Within Species” on page 647 of your textbook to review these concepts. Record you findings in your course folder.
Self-Check
SC 2. Why is your mitochondrial DNA identical to the mitochondrial DNA of your mother, rather than that of your father?
SC 3. Give two examples of ways that the study of DNA sequences can help scientists learn about genetic relationships, genetic variations, or evolution.
SC 4. What was the objective of the Human Genome Project?
Self-Check Answers
SC 2. Your mitochondrial DNA is identical to the mitochondrial DNA of your mother, as your father’s sperm contributes essentially no cytoplasm and ,therefore, no cytoplasmic organelles to its offspring. On the other hand, your mother’s egg provided most of the cytoplasm and cytoplasmic organelles, including the mitochondria. While the DNA in the nuclei of your cells is made up of an equal combination of DNA from your mother and your father, your mtDNA came from the cytoplasm of your mother’s ovum.
SC 3. DNA allows scientists to study genetic variations among individuals of the same species as well as the genetic variation between different species. This helps scientists to track the evolution of a species through time. Comparing the DNA of ancient plants, animals, and even bacteria with the DNA of their modern counterparts, can reveal such varied information as the ancestry of modern organisms, the movement of populations through time, the evolution of particular disease-causing bacteria, and the way ecosystems respond to climate change.
SC 4. The objective of the Human Genome Project was to determine the sequence of nitrogen bases for the DNA in the chromosomes of the entire human genome. The Human Genome Project is an important step in understanding how genes determine genetic characteristics. This understanding can be applied to medical genetics and the treatment of disease as well as to other sciences.
Module 7: Lesson 6 Assignment
In a paragraph, you will explain how the base sequences in nucleic acids contained in the nucleus, mitochondrion, and chloroplasts give evidence of the relationships among organisms of different species. Check the marking rubric found in the assignment document for direction on how to prepare your paragraph.
Retrieve your copy of Module 7: Lesson 6 Assignment that you saved to your computer earlier in this lesson. Complete Part 2 involving an explanation of the use of DNA in tracing ancestory. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.
Going Beyond
Hypothesize as to how Y chromosomes could be used to trace ancestry. Would you be tracing maternal or paternal ancestry using this chromosome? Discuss your ideas with your teacher and your classmates.
Module 7: Lesson 6 Assignment
Submit your completed Module 7: Lesson 6 Assignment to your teacher for assessment.