Background and Introduction | Unique You | Nature or Nurture? | Face It!
Camp-In Curriculum: Genetics
These activities introduce ideas about heredity, observing the differences and similarities in a population, and modeling how inheritance works. Campers can think about organisms as systems in which coded information is shared in genes.
Many genetics books and curricula ask students to create and analyze their own family trees. Given the complexities of modern families, single parent households, step-families, adopted families, etc., please be cautious about asking children to compare their physical traits with their biological relatives. The activity outlined here enables children to model inheritance patterns in a more sensitive way.
Genetics is the study of how characteristics of living things are passed from one generation to the next.
Until 150 years ago, people believed that parents' characteristics blended together in their children. In the 1830s, Gregor Mendel, a Moravian monk, conducted experiments cross-breeding peas. He determined that certain traits, such as color, shape, and size, were passing from the parents to their offspring in a predictable way. He called these characteristics "factors." We now call them genes.
Mendel observed that the traits of the parents did not blend in the offspring. A six-foot-tall pea plant crossed with a one-foot-tall pea plant did not produce a three-foot-tall pea plant. All the crosses with the six-foot plants produced six-foot plants. Mendel hypothesized that each organism has a pair of factors that determine each trait. Offspring receive one half of each pair from each parent. In the offspring, the two factors, or genes, work together. He discovered that one form of the trait was almost always stronger than the other (dominant). Further experiments revealed that the hidden (recessive) gene can reappear in future generations, if it is combined with a recessive gene like itself.
Although Mendel recorded his observations, published them, and sent them to many leading institutions, his work was ignored. Mendel's work was rediscovered around the turn of the century. However, it was still unclear what the precise agent of inheritance was and how it functioned. In 1907 Thomas Morgan demonstrated that the controlling mechanisms of inheritance are contained in chromosomes inside each cell. The work of Mendel, Morgan, and others showed that mechanisms for inheritance existed at the level of cells. The term gene was accepted as a description of the genetic mechanism located in the chromosome.
In the 1930s, our understanding of genetics was aided by the discovery that the molecule deoxyribonucleic acid (DNA) is present in the nucleus of virtually every cell, but its function and shape were a mystery. In the 1950s, DNA was identified as the carrier of genetic information. Rosalind Franklin conducted x-ray diffraction studies of the DNA molecule in 1951, which suggested DNA had a helical structure. At the same time James Watson and Francis Crick were exploring how DNA functioned. They realized that the form of a double helix would not only explain the shape of DNA, but also explain how the molecule passes on information. After physically building a model of their proposed structure, they realized they had solved the riddle of how genetic information is transmitted. In 1962, Watson, Crick and another researcher Maurice Wilkins, received the Nobel Prize for their discovery. Unfortunately, Rosalind Franklin's death in 1958 at age 38 prevented her from sharing in their recognition.
We now know that in the center of every cell are pairs of chromosomes. Each chromosome is a tightly wound thread of DNA. These very long threads contain repetitions and variations of four different chemicals, adenine (A), thymine (T), cytosine (C) and guanine (G). Segments of these strings of DNA are called genes. Genes have from a few hundred pairs to many thousands of pairs of As, Ts, Cs, and Gs joined together in a precise code that is unique to each gene. Human DNA contains 3 billion of these pairs. Genes are recipes for making proteins. These proteins determine how an organism grows and what it is like. Some proteins make cells, other proteins tell the cells how to function. Your cells are making new cells all of the time. Different genes are active in different cells at different times.
There is a special kind of cell division that happens in sexual reproduction to form the cells that are passed on to the next generation. This division, meiosis, results in cells that have half the number of chromosomes as the original cell. Each parent produces cells that contain half of his or her genetic information. When these two special cells merge together, the two half sets of chromosomes combine to produce a fertilized egg or seed. In this way an organism inherits some traits from its mother and some from its father. The reason every organism is different is because each mixture of genes is slightly different.
A new person starts as just one tiny cell with 23 pairs of chromosomes containing a unique mixture of genes. As the person grows, the cells divide. The first cell becomes two cells, the two become four and so on. Before each cell divides, the DNA is copied and each new cell receives one of these copies.
Mendel's theory about simple dominant factors was the start of our understanding of heredity. We now know that most traits are influenced by many pairs of genes working together. Sometimes there is no dominant gene, and the offspring actually is a blend of both traits. Genes give instructions about what can be done, but genes also have to work with the environment in which the organism grows. Short parents can produce tall children. Tall parents can produce short children. Your height can also be influenced by your diet.
Today, geneticists around the world are working on mapping the entire sequence of the billions of chemicals that compose human DNA. They have already charted over 2,300 of the suspected 100,000 genes that make up the human genome.
Benchmarks for Science Literacy 0
Experiment -- Unique You
Background for Instructors
This is a binary sorting method, similar to what is used by many computer programs. For every trait, campers either possess the trait or do not possess the trait. Each step of the sort has two possible outcomes, just like an electronic signal is either on or off. For example, don't divide into groups by shirt color. Instead divide into two groups, white shirts and not white shirts.
Activity -- Nature or Nurture?
Background for Instructors
Determining inheritability is a complicated subject. Often things are said to be 80% inherited or 20% inherited. Most patterns of inheritance are not simple. Many traits are controlled by multiple genes. There are still fervent debates about many traits, such as intelligence or certain behaviors.
Activity -- Face It!
Background for Instructors
The introductions to this section and the previous activity indicate the complexity in determining what features of our appearance are genetically determined. Nevertheless, this activity introduces some features that are generally accepted to be inherited. Several types of inheritance are described:
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