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Unit 8: Genetics. Day One: Mendelian Genetics! . 1 JOHANN GREGOR MENDEL (1822-1884) . Father of Genetics – the scientific study of heredity Heredity – delivery of characteristics from one generation to the next. 2 Mendel’s Work. experiments took him eight years (1856-1863)
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Unit 8: Genetics Day One: Mendelian Genetics!
1 JOHANN GREGOR MENDEL (1822-1884) • Father of Genetics – the scientific study of heredity • Heredity – delivery of characteristics from one generation to the next
2 Mendel’s Work • experiments took him eight years (1856-1863) • published his results in 1865 • grew over 10,000 pea plants • kept track of progeny number and type • Mendel's work and his Laws of Inheritance were not appreciated in his time. It wasn't until 1900, after the rediscovery of his Laws, that his experimental results were understood.
simple, easy to see traits easy to grow and maintain easy to make crosses short reproductive cycle many offspring (hundreds) other species used fruit flies (Drosophila melanogaster) Can’t use larger animals because their reproductive cycle takes too long. 3 Why pea plants?
4 plant reproduction Usually pea plants are self-pollinating, meaning that pollen fertilizes an egg of the same flower. This produces offspring identical to the parent plant, which is called “true breeding.”
5 traits Mendel studied Traits: a specific characteristic of an individual. Mendel studied seven pea plant traits.
6 basic terminology • phenotype – appearance (green, yellow, round, wrinkled, tall, short) • genotype – genetic makeup (GG, Gg, gg, RR, Rr, rr, TT, Tt, tt)
Genes – factors that are passed from parents to offspringalleles – different forms of a geneExample: gene for plant height has two alleles, tall and short 7 More Basic Terminology You Need to Know Different genotypes: homozygous dominant – pure dominant TT homozygous recessive – pure recessive tt heterozygous – one allele for each (hybrid) Tt
8 dominance • The principle of dominance states that some alleles are dominant and others are recessive.
9 self-pollination: what happens naturally– creating purebreds – true-breeding
10 hybridization hybrid – mix of two purebreds Mendel achieved this through cross-pollination. He removed the stamen from one plant and the pistil from another plant and did the pollination himself, which allowed him to create offspring with two different parents.
11 Results of Hybrid crosses For each trait, Mendel cross-pollinated purebreds of each type, creating hybrids for that trait. For instance, he crossed purebred tall with purebred short. In another, he crossed purebred yellow seeds with purebred green seeds. He did this for all seven traits. In every case, one of the traits disappeared completely in the offspring. His assumption: when the two different alleles are found together, one must be dominant so that it is the only one that is expressed.
12 Where did the other traits go? Mendel was curious – did the recessive traits disappear, or were they still there and just not expressed? To find out, he took offspring from the first cross and crossed them together. He did this by allowing them to self-pollinate. This produced a second generation of offspring. What did he find? The recessive traits reappeared in this second generation. So, it didn’t disappear; it was just masked or hidden by the dominant allele.
13 generations • P generation – purebred parents • F1 – first filial generation(filius and filia = son) - created by crossing two purebred parents - hybrids • F2 - second filial generation - created by crossing two F1 (incest)
14 laws of inheritance • Gregor Mendel discovered the fundamental laws of inheritance. • genes come in pairs • genes are inherited as distinct units, one from each parent 1. dominant/recessive 2. segregation 3. independent assortment • He recognized the mathematical patterns of inheritance from one generation to the next.
15 segregation = separation • the two alleles are segregated from each other so that each gamete carries only a single copy of each gene • each F1 plant produces two types of gametes
16 probability and number • Probability is the likelihood that something will occur. • Probabilities are not precise. • Probability predicts the average outcome of a large number of events.
17 Punnettsquares • The principles of probability can be used to predict the outcomes of genetic crosses.
19 test cross To identify the genotype of yellow-seeded pea plants as either homozygous dominant (YY) or heterozygous (Yy), you could do a test cross with plants of genotype yy.
