1 / 16

Genetics and Mendel

Genetics and Mendel. Mendel’s Work. Mendel’s pea experiments led him to conclude that inheritance is determined by factors ( genes ) passed from one generation to the next. These factors control all the various traits of an organism and may come in different forms ( alleles ).

sharice
Download Presentation

Genetics and Mendel

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Genetics and Mendel

  2. Mendel’s Work • Mendel’s pea experiments led him to conclude that inheritance is determined by factors (genes) passed from one generation to the next. • These factors control all the various traits of an organism and may come in different forms (alleles).

  3. Principle of Dominance • For a specific gene one allele for a trait is dominant over the others (recessive). • If the dominant allele is present, this is the characteristic the organism displays. • The only time the recessive allele is expressed is if there is NO dominant allele.

  4. Dominance The F1 generation from a cross of true-breeding plants are all Hybrids. The F2 generation shows the return of the recessive allele.

  5. Segregation • Mendel showed that the recessive allele does not disappear. Crossing 2 Hybrid plants (F1) produced offspring that exhibited the recessive allele once again. • For all the F2 offspring produced about ¼ of them exhibited the recessive allele. • 3:1 ratio of Dominant:Recessive traits displayed.

  6. Segregation • How did this occur? • Mendel suggested that the 2 alleles for a specific trait that an organism contains segregate during sex cell formation (meiosis). • Effectively, an organism will make two types of gametes: 1 type has one allele for a gene and the 2nd type holds the other allele. • This way, of the 2 possible alleles a parent can contribute to offspring only one allele from each parent and becomes somewhat a game of chance.

  7. Punnett Squares • We can use Punnett Squares to predict the outcome of a genetic cross for a particular trait. • Homozygous: Contains 2 of the same allele for a trait. • Heterozygous: Contains 2 different alleles for a trait (hybrids!) • Genotype: The genetic makeup of an organism for a trait. • Phenotype: The physical characteristic displayed for a specific trait.

  8. Independent Assortment • Mendel then looked at the bigger picture. What happens to all of the genes of an organism during gamete formation. • Does segregation of one gene influence another? In other words as one gene segregates does it impact the segregation of another? • Mendel examined a cross of plants for two specific traits

  9. Independent Assortment • He crossed a plant that was Homozygous for yellow round peas (YYRR) with a plant that was Homozygous wrinkled green peas (yyrr). • The F1 generation was all yellow round as expected. • What’s their genotype?__________

  10. Independent Assortment • Mendel then let the plants self-pollinate (just as before) to produce the F2 generation. • Of the resulting F2 generation every possible combination of traits were shown. • 556 seeds produced 315 were round/yellow. • 32 were wrinkled/green • 209 were a combination of phenotypes round/green and wrinkled/yellow • The results supports the idea that traits segregate separately.

  11. Independent Assortment • Genes for different traits segregate independently during the formation of gametes. • One gene’s segregation does not influence another’s.

  12. Exceptions to Mendel • Mendel’s findings and rules hold true for many cases in genetics. But there are some exceptions. (Figures, right?) • Some genes do not have a dominant or recessive form, and some have more than just 2 alleles.

  13. Incomplete Dominance • One allele is not dominant over another. • The result of these crosses produce heterozygous offspring showing traits between both homozygous parents. • Example: snapdragon

  14. Codominance • Similar to incomplete dominance. In codominant cases both alleles contribute to the organism’s phenotype. • What you see is both phenotypes being expressed! • Example: Roan cattle; color of chicken feathers

  15. Multiple Alleles • Many genes have more than 2 possible forms (alleles) in a population. • Makes for greater diversity for a trait. • Example: Blood type in humans

  16. Polygenetic Traits • Not every trait is controlled by one gene. Often, multiple genes influence how certain traits are displayed. • Traits controlled by two or more genes are said to be polygenetic. • Example: Skin color in humans, fruit fly eye color.

More Related