Module 7 Molecular Genetics

Lesson 3.7.6

3.7.6 page 4

Going Beyond

Real World Applications

Research some real examples of DNA fingerprint analysis being used to solve crimes or identify people.

Read

Evolutionary Relationships Between Species

To study how different birds were related in the 1960’s, biologists would have looked at their anatomical similarities and differences. For example, the DNA of chimpanzees is 98% the same as human DNA, and the genetic similarity between 2 humans is more then 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. Read more about this on page 647 of your textbook.

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

Up to this point we have only been discussing nuclear DNA, but 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 ended up in the cell is called the endosymbiont theory and can be read about on page 647 of your textbook

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 your mother. When you go back generations in your family tree you will see that many men and women contributed to your nuclear DNA makeup, 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 they are related. The more dissimilar the mtDNA, the more mutations must have occurred indicating more time on the evolutionary path must have elapsed.

Self-Check

SC 1. Why is your mitochondrial DNA identical to the mitochondrial DNA of your mother, rather than your father?

SC 2. Give two examples of ways that the study of DNA sequences can help scientists learn about genetic relationships, genetic variations, or evolution.

SC 3. What was the objective of the Human Genome Project?

Check your work.

Lesson Summary

During this lesson you have seen how the knowledge of the human genome gained through the Human Genome Project has helped forward the areas of forensics and evolution. You have seen how gel electrophoresis is used to created DNA fingerprints unique to each individual. By completing the lab and self-check you applied your knowledge of DNA fingerprints to isolate “genes” responsible for specific traits, as were you able to identify twins and the biological parents of a child. You have also read about the evidence for evolutionary relationships that can be obtained from nuclear DNA, mitochondrial DNA and chromosomal DNA.

Lesson Glossary

chloroplast DNA (cpDNA): circular molecules of DNA found in the chloroplasts of plants; codes for the function of photosynthesis

DNA fingerprint: the pattern of bands into which DNA fragments sort during gel electrophoresis

This pattern is unique for every individual except twins, triplets etc.

gel electrophoresis: tool used to separate molecules according to their mass and charge; can be used to separate fragments of DNA

Human Genome Project: joint effort of thousands of researchers from laboratories worldwide that determined the sequence of the three billion base pairs making up the human genome.

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)