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Genetics Notes. Article selections from “Introduction to Genetics” at Overview.

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genetics notes

Genetics Notes

Article selections from “Introduction to Genetics” at


Genetics is the study of genes, and studies what genes are and how they work. Genes are how living organisms inherit features from their ancestors; for example, children usually look like their parents because they have inherited their parents' genes. Genetics tries to identify which features are inherited, and explain how these features pass from generation to generation.

  • Living things (organisms) inherit genes from their ancestors (parents, grandparents, great-grandparents, etc.).
  • Genetics is the science that studies which features or traits are inherited.
nature vs nurture
Nature vs. Nurture

In genetics, a feature of a living thing is called a "trait". Some traits are part of an organism's physical appearance; such as a person's eye-color, height or weight. Other sorts of traits are not easily seen and include blood types or resistance to diseases. The way our genes and environment interact to produce a trait can be complicated. For example, the chances of somebody dying of cancer or heart disease seems to depend on both their genes and their lifestyle.

  • A feature or characteristic is also know as a trait.
  • Traits include physical appearance AND unseen traits (for example, blood type and resistance to disease).
  • Genes and the environment interact to shape an organism’s traits.
genes carry information
Genes Carry Information

Genes are made from a long molecule called DNA, which is copied and inherited across generations. DNA is made of simple units that line up in a particular order within this large molecule. The order of these units carries genetic information, similar to how the order of letters on a page carries information. The language used by DNA is called the genetic code, which allows the genetic machinery to read the information in the genes in triplet sets of codons. This information is the instructions for constructing and operating a living organism.

  • Genes are made from DNA, which is copied and passed on through generations.
  • The information in the genes- the order of the letters in the code- carries instructions for building and operating a living organism.

The information within a particular gene is not always exactly the same between one organism and another, so different copies of a gene do not always give exactly the same instructions. Each unique form of a single gene is called an allele. As an example, one allele for the gene for hair color could instruct the body to produce a lot of pigment, producing black hair, while a different allele of the same gene might give garbled instructions that fail to produce any pigment, giving white hair. Mutations are random changes in genes, and can create new alleles. Mutations can also produce new traits, such as when mutations to an allele for black hair produce a new allele for white hair. This appearance of new traits is important in evolution.

  • A unique form of a gene- one version of a gene- is called an allele.
  • Mutations are random changes in genes, and can create new alleles.
  • New alleles can produce new traits.
  • The appearance of new traits is important in evolution.
genes make proteins
Genes Make Proteins

The function of genes is to provide the information needed to make molecules called proteins in cells. Cells are the smallest independent parts of organisms: the human body contains about 100 trillion cells, while very small organisms like bacteria are just one single cell. A cell is like a miniature and very complex factory that can make all the parts needed to produce a copy of itself, which happens when cells divide.

  • Genes carry information to make proteins.
  • Almost all parts of an organism are made by proteins or are made of proteins (or both).
  • Using genetic information, a cell can make all the parts needed to make a copy of itself.
genes proteins do the work of cells
Genes & Proteins do the Work of Cells

There is a simple division of labor in cells - genes give instructions and proteins carry out these instructions, tasks like building a new copy of a cell, or repairing damage. Each type of protein is a specialist that only does one job, so if a cell needs to do something new, it must make a new protein to do this job. Similarly, if a cell needs to do something faster or slower than before, it makes more or less of the protein responsible. Genes tell cells what to do by telling them which proteins to make and in what amounts.

  • Genes give instructions; proteins carry out the instructions.
  • Proteins do tasks such as copying the cell or repairing damage to the cell (also many, many other things that keep the cell- and the organism- alive).
genes are copied
Genes are Copied

Genes are copied each time a cell divides into two new cells. The process that copies DNA is called DNA replication. It is through a similar process that a child inherits genes from its parents, when a copy from the mother is mixed with a copy from the father.

  • When genes are copied so the cell can divide, it is called DNA replication.
nucleotides structure of dna
Nucleotides & Structure of DNA

DNA can be copied very easily and accurately because each piece of DNA can direct the creation of a new copy of its information. This is because DNA is made of two strands that pair together like the two sides of a zipper. The nucleotides are in the center, like the teeth in the zipper, and pair up to hold the two strands together. Importantly, the four different sorts of nucleotides are different shapes, so for the strands to close up properly, an A nucleotide must go opposite a T nucleotide, and a G opposite a C.This exact pairing is called base pairing.

  • There are four nucleotides, read like letters, in the genetic code, and they always match up the same way: T pairs with A;C pairs with G.
  • DNA is shaped like a double spiral (a double helix). The nucleotides hold it together in the center, like the teeth of a zipper.
dna replication and mutation
DNA Replication and Mutation

When DNA is copied, the two strands of the old DNA are pulled apart by enzymes that move along each of the two single strands pairing up new nucleotide units and then zipping the strands closed. This produces two new pieces of DNA, each containing one strand from the old DNA and one newly made strand. This process isn't perfect and sometimes the proteins make mistakes and put the wrong nucleotide into the strand they are building. This causes a change in the sequence of that gene. These changes in DNA sequence are called mutations. Mutations produce new alleles of genes. Sometimes these changes stop the gene from working properly. In other cases these mutations can change what the gene does or even let it do its job a little better than before.These mutations and their effects on the traits of organisms are one of the causes of evolution.

  • DNA is copied when enzymes pull the 2 strands apart and pair up new nucleotide units to produce two copies of DNA.
  • The copying process isn’t perfect~ mistakes cause mutations, which produce new alleles. Mutations can stop genes from working correctly, change what the gene does, let the gene do its job better-- or it can be neutral, with no benefits or drawbacks.