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Genetics - The Basics Once Upon a Time… ...there was a monk named Gregor Mendel. Once Upon a Time… Mendel was a monk that lived in Austria in the mid19th century. While living in a monastery in Brno he grew many different generations of pea plants and recorded his observations from these generations He looked at many characteristics like flower colour and pea shape and pea colour. Once Upon a Time… He referred to the parent generation (the start) as P The generation that came after that was then known as F1 generation The generation that came after F1 was then named F2 and so on and so forth Once Upon a Time… Mendel used the pea because the physical traits they were showing came in two forms so they were easier to track and to analyze He also used the pea plants because they were easy to manipulate and create more of - they use selfpollination reproductive strategies Once Upon a Time… Mendel, as many scientists in history, died before his work became recognized in the scientific world but today we use his research and discoveries as the basis for many genetic research When looking at basic laws of inheritance and basic traits we are studying Mendelian genetics and looking at Mendelian traits World Dominance-ation... When Mendel used pollen from the pea plant with round seeds to fertilized a pea plant with wrinkled seeds, he found that all the offspring (progeny) had round seeds He didn’t stop there, he then used a plant with wrinkled seeds to pollinate one with round seeds and again found that all the offspring had round seeds World Dominance-ation... This experiment showed that the round seeds were the dominant trait, regardless of parentage. This meant that if the dominant allele is present in a chromosome, this is the trait that you will see Recessiveness and Alleles The other gene that is not being expressed physically is then called the recessive trait. With this knowledge, Mendel realized that there must be ways for there to be two or more different forms of ‘factors’ (genes) that give rise to different traits These different forms are called alleles Dominant vs. Recessive When looking at the dominant alleles, we write it as a capital letter Example: dominant allele for seed shape is round therefore we would represent it with a capital R When looking at the recessive alleles, we write it as a lowercase letter Example: recessive allele for seed shape is wrinkled therefore we would represent it with a lowercase r Principle of Segregation Mendel’s research began to focus on the dominant and recessive traits expressed by the pea plants When he crossed pure round seed plants with pure wrinkled plants, 100% of the F1 generation had round seeds He was astonished to find that 25% of the F2 generation of these seeds had wrinkled seeds! Principle of Segregation He performed multiple tests with the same plants and found that for the F2 generation he continued to get the same 3:1 ratio (75 % round to 25% wrinkled) To explain this, Mendel stated that each seed had 2 copies (alleles) of each gene that can be the same or different A round seed must always carry at least one R allele but wrinkled seeds must always carry two r alleles (rr) Principle of Segregation When two alleles are the same and paired together, they are called homozygous When the alleles are different, and paired together, they are called heterozygous The genes that are expressed are called genotype The physical appearance is called phenotype Principle of Segregation Mendel also said that two copies of a gene undergo segregation during meiosis (separation of the alleles) Questions page 600 #1, 2, 5