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Transcript
Genetics Transmission Genetics What is inherited ? How is it inherited ? What is the role of chance in heredity ? Why do valued traits sometimes disappear then reappear in only some offspring? Genetics – the study of heredity – how genes or traits are passed to generations What are some examples of traits? ______________ ______________ ______________ Our genes code for these traits!!!!! Alleles •Distinguishable units of inheritance •Alternative forms of a single gene Example of traits: Examples of Alleles Eye color Skin color Height Hair texture Brown or blue Albino or pigmented Tall or short Curly or straight What is inherited A Trait!! Genotype – units of inheritance – genetic traits Phenotype – observable traits – What you can see, hear, taste, smell, and touch – “Physical” Characteristics Gregor Mendel (1822-1884) Augustinian monk Expert plant breeder Experiments with garden peas Father of Genetics Mendel studied plants with different traits. One factor or trait he observed was tall plants and short plants. He used pure (true breeding) plants. He crossed pollinated these plants. He crossed true breeding tall plants (TT) with true breeding short (tt) plants. Found that all plants in the F1 generation were tall. (Tt) P (Parental) Generation F 1 (Filial ) Generation F 2 Generation Then Mendel crossed the plants with the Tt genotype and it produced 75% tall and 25% short. From this he formed a law of dominance, because he knew that one allele was dominant over the other. In this case which is dominant, short or tall? Which is recessive? IN THE END…… -He concluded that traits are inherited through the passing of factors from parents to offspring. -He created 3 Laws 1st Law – Law of Dominance – Some alleles will be shown while some other alleles will not be shown. In other words some alleles are shown, while others are hidden. - The trait that is shown is considered dominant because it masked (dominated) over the other traits. Trait Characteristics Dominant – “‘Stronger’” trait – The trait you see more often, or covers – Expressed by a capital letter Y Recessive – “‘Weaker’” trait – The trait you see less often, or being masked/covered – Expressed by a lower case letter y Homo- means same, Hetero – means different Homozygous is two of the same allele Heterozygous is two different allele What would be an example of Homozygous Dominant? ______ Heterozygous Dominant? _____ ___ Homozygous Recessive? ________ 2nd Law – Law of Segregation – States that during meiosis two alleles will separate. Recall Meiosis – you create gametes. Law of Segregation ensures that each gamete will have one allele from the allele pair. Law of Independent Assortment – States that alleles distribute randomly or independently during meiosis. YyRr – gametes ____YR______ _______Yr________ _______yR________ _______yr________ Monohybrids are used to view the outcomes in offspring examining only one trait A punnett square is a visual aid that is used to view traits. Punnett Square The probability is the chance of a certain outcome. Example: What is the chance of either having a girl or boy? Each outcome will be independent of the other. Dihybrids Looks at the possibilities of two Different traits.