Welcome to the complex and fascinating world of genetics. Genetics is all about physical traits and the DNA code that supplies the building plans for any organism.
This chapter explains what the field of genetics is and what geneticists do. You get an introduction to the big picture and a glimpse at some of the details found in other chapters of this book.
What Is Genetics?
Genetics is the field of science that examines how traits are passed from one generation to the next. Simply put, genetics affects everything about every living thing on earth.
An organism’s genes, snippets of DNA that are the fundamental units of heredity, control how the organism looks, behaves, and reproduces. Because all biology depends on genes, understanding genetics as a foundation for all other life sciences, including agriculture and medicine, is critical.
From a historical point of view, genetics is still a young science.
The principles that govern inheritance of traits by one generation from another were described (and promptly lost) less than 150 years ago.
Around the turn of the 20th century, the laws of inheritance were rediscovered, an event that transformed biology forever.
But even then, the importance of the star of the genetics show, DNA, wasn’t really understood until the 1950s. Now, technology is helping geneticists push the envelope of knowledge every day.
Genetics is generally divided into four major subdivisions:
✓ Classical, or Mendelian, genetics: A discipline that describes how physical characteristics (traits) are passed along from one generation to another.
✓ Molecular genetics: The study of the chemical and physical structures of DNA, its close cousin RNA, and proteins. Molecular genetics also covers how genes do their jobs.
✓ Population Genetics: Adivision of genetics that looks at the genetic makeup of larger groups.
✓ Quantitative genetics: A highly mathematical field that examines the statistical relationships between genes and the traits they encode.
In the academic world, many genetics courses begin with classical genetics and proceed through molecular genetics, with a nod to population, evolutionary, or quantitative genetics.
This book follows the same path, because each division of knowledge builds on the one before it.
That said, it’s perfectly okay, and very easy, to jump around among disciplines.
No matter how you take on reading this book, I provide lots of cross references to help you stay on track.
Classical genetics: Transmitting traits from generation to generation.
At its heart, classical genetics is the genetics of individuals and their families. It focuses mostly on studying physical traits, or phenotypes, as a stand-in for the genes that control appearance.
Gregor Mendel, a humble monk and part-time scientist, founded the entire discipline of genetics.
Mendel was a gardener with an insatiable curiosity to go along with his green thumb. His observations may have been simple, but his conclusions were jaw-droppingly elegant.
This man had no access to technology, computers, or a pocket calculator, yet he determined, with keen accuracy, exactly how inheritance works.
Classical genetics is sometimes referred to as:
✓ Mendelian genetics: You start a new scientific discipline, and it gets named after you. Seems fair.
✓ Transmission genetics: This term refers to the fact that classical genetics describes how traits are passed on, or transmitted, by parents to their offspring.
No matter what you call it, classical genetics includes the study of cells and chromosomes.
Cell division is the machine that drives inheritance, but you don’t have to understand combustion engines to drive a car, right? Likewise, you can dive straight into simple inheritance and work up to more complicated forms of inheritance without knowing anything whatsoever about cell division. (Mendel didn’t know anything about chromosomes and cells when he figured this whole thing out, by the way.)
The genetics of sex and reproduction are also part of classical genetics.
Various combinations of genes and chromosomes (strands of DNA) determine sex, as in maleness and femaleness.
But the subject of sex gets even more complicated (and interesting): The environment plays a role in determining the sex of some organisms (like crocodiles and turtles), and other organisms can even change sex with a change of address.
If I’ve piqued your interest, you can find out all the slightly kinky details in upcoming chapters.
Classical genetics provides the framework for many subdisciplines. Genetic counseling depends heavily on understanding patterns of inheritance to interpret people’s medical histories from a genetics perspective.
The study of chromosome disorders such as Down syndrome relies on cell biology and an understanding of what happens during cell division. Forensics also uses Mendelian genetics to determine paternity and to work out who’s who with DNA fingerprinting.
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Genetics
Short StoryMy goal is to explain every topic so that anyone, even someone without any genetics background at all, can follow the subject and understand how it works. As in the first, I include many examples from the frontiers of research. I also make sure that...
