So in this unit you will learn about genetics and how genes influence your physical being and- to some extent- your non physical being. Genetics is the study of chromosomes, DNA, genes, and nucleotide. Chromosomes are found in the nucleus of all living cells. Different species have different numbers of chromosomes.
Chromosomes are made up of DNA (Deoxyribonucleic acid). DNA is the largest chemical molecule in your body (about 6 feet long) and contains on it genes. Genes are sequences of nucleotides which the ribosomes might read so that proteins may be produced to build physical parts, influence processes within organisms, and help to keep the body running. It is important to note that ONE GENE MAKES ONE PROTEIN. However, a protein may influence or build many different traits OR a gene might turn on / off another gene that will make one protein that might influence or build many different other traits! It all gets very complicated!
Genes are made up of nucleotide sequences. That is to say there is a specific pattern of nucleotides on a gene and that pattern is what is read by the ribosome.....see above!
Adenine, Thymine, Cytosine, and Guanine are the only four nucleotides that make up DNA. These and only these four chemicals are responsible for all life on the planet. Without these nucleotides, the ribosomes wouldn't be able to make the proteins that are such an intricate and crucial part of our lives. These bases are found as base pairs. The base pairs are Adenine with Thymine and Guanine with Cytosine. A scientist by the name of Chargoff discovered these pairings through what is now known as Chargoff's Ratios. . . . .
Genotype and Phenotype
To summarize, nucleotides make up genes and genes make up DNA. DNA, when all coiled up, makes chromosomes and chromosomes are found in the nucleus of every living thing on the planet (or floating around in the cytoplasm of viruses and their ilk).
Bases and base pairs are nucleotides. Nucleotides are Adenine, Thymine, Cytosine, and Guanine. When a string of nucleotides is being read by the ribosome, the ribosome is reading the bases three at a time and lumping together amino acids based on the pattern. These "piles" of amino acids make proteins and proteins make life (or help life to function!) When the bases are paired with their complimentary nucleotide we call them base pairs and base pairs make up the rungs of the DNA "ladder". The outside of that ladder is sugar and phospate.
That brings us to today's lesson: Genotypes and Phenotypes. . . . .
Reproduction of organisms falls under two different and distinct processes:
1. Sexual reproduction. This form of reproduction uses sperm and egg cells and a process of fertilization where the DNA of the sperm merges with the DNA of the egg. It requires a male and female. Sexual reproduction may be internal (mammals, birds, repiles) or external (amphibians, fish, plants). The pros of sexual reproduction are the mixing of the DNA which causes variation. Variation is a prime factor in a species continued evolution and existance in a changing environment. The cons of sexual reproduction is that it takes a lot longer to produce offsping- relatively.
2. Asexual reproduction. Asexual reproduction is mitosis, "cloning", or "copying". This form of reproduction DOES NOT use egg or sperm cells. There is one "parent" cell which copies its DNA and splits- mitosis. The pros to asexual reproduciton is speed! News cells are formed at a rapid and exponential rate. The cons of asexual reproduction is that all the "offspring" are the same as the "parent". This is bad because if a factor is able to kill one cell it can, theoretically, kill all of them. . . . .
Now that we have explored genes, how they are represented (genotypes), how they are made up (a pair of alleles), and how those alleles travel through time to influence future traits, we can move into predicting those traits.
Punnet squares are a tool used by geneticists to try and predict the probability of genotypes in future generations. For your purposes, punnet squares will always come in the form of a word problem. The steps to be used- no matter how complicated the word problem seems- are below: . . . .
Genetic Heredity- Mendelian
Today you were born, grew up, went through puberty, met the love of your life, got married, had children, grew old, and had grandchildren! Quite the busy science class!
Beaker Babies was an activity to show you how heredity works. Heredity is the passing of alleles, genes, from one generation to another in some random way through sexual OR asedual reproduction. In Beaker Babies, it was sexual.
Dominant and recessive alleles from your mother and father were passed down to you (forming genotypes). They received their alleles from their parents who received their genes from their parents and so on. Dominant genes tend to be expressed more often in a family because they have greater influence over the phenotypes expressed. Recessive genes are not gone! They are hidden by the dominant gene and may be expressed in future generations- depending on who marries who and has kids. . . . .
Pedigrees are "family trees" that show specific genotypes for a specific phenotype. They show hereditary information for a particular family blood line. Depending on where you start you will have varying generations of genetic information. The pedigree is made up of many symbols (which can be found in your notes) but basically looks something like this: . . . .
Transcription and Translation ()
So far we have learned about DNA, genes, nucleotides and how those bits of genetic information can be passed from generation to generation through the process of inheritance. We have also explored the concept of "one gene, one protein" and how that protein (or a bunch of proteins) make up the phenotypes of organisms.
Today we get to the mechanism, the process that turns chemical genetic code into tangible, observable, living stuff. That process is called Transcription and Translation. Transcription is when a gene on the DNA- which is locked inside the nucleus- is copied and produces RNA- which can leave the nucleus and be read by the ribosomes. Translation is when the ribosome reads the RNA- three nucleotides at a time- and produces a protein based on that genetic sequence and the help of transfer RNA (tRNA).
The movie referenced above is very good at showing this (as well as multiple YouTube videos) but I will try to explain it here using a very simple example.
Lets say the gene on the DNA looks like this . . . .
Genetic Mutations are any change in the genetic code. It's that simple. Changes to the genetic code have varying amounts of affect. In some cases the affect is very small and in other cases the affect can be really great- so great that the oranism has an advantage over the others in its population or so great that it kills off the organism.
Genetic mutations cannot be forced by the organism itself (by humans- yes, but not by the organism). For example, if a mouse lives in a particular part of the world and the area gets colder and colder, the mouse cannot simply "will" its genes to change so that it might be furrier or fatter. IF the genes mutate to produce those effects, the mouse might survive the climate. IF the mouse cannot change fast enough, it may die out. If there are NO mice with a mutation for heavier fur or more fat, then the entire population may go extinct from that area.
Mutations fall into a couple of categories:
Induced: Whereby the environment causes the mutation(s). Things like the sun, radioactivity, toxic water, etc. may induce a genetic mutation.
Natural: Sometimes "things just happen". Sometimes the genetic code simply mutates on its own. . . . .
Genetic engineering is the process of manipulating the genetic information within various organisms. Genetic engineering can take the form of selective breeding, Transgenics, and Cloning.
Selective Breeding: Selective breeding is also called Artificial Selection because it involves humans selecting which animals or plants breed with which other animals and plants. Farmers have been doing this since the dawn of farming! If an animal or plant has sought after traits (like speed, size, coloration, strength, product production (meat, milk, wool) etc. then that farmer will try and produce offpsring from that animal or plant with the same or enhanced, preferred traits. This can take a long time- many generations- and you are not always gauranteed of a favorable outcome.
Every dog on the planet is a product of selective breeding! Those enormous pumpkins you see at Halloween are the product of selective breeding. Racehoreses are often a product of selective breeding. Just about everything you eat or get from a farm is the result of that farmer and farmers before them intensively focused on selective breeding. . . . .