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Delving into Genetics: Understanding Traits and Inheritance

Explore the fascinating world of genetics and inheritance through the pioneering work of Gregor Mendel with pea plants. Learn about alleles, Punnett squares, and how traits are passed down from generation to generation.

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Delving into Genetics: Understanding Traits and Inheritance

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  1. Chapter 11 - Genetics

  2. What is Genetics? • The scientific study of heredity. • What is heredity? • The passing of traits from one generation to the next • Characteristics that are inherited from each parent • Tall or Short • Blonde or Brown Hair • Blue or Green Eyes

  3. The Father of Genetics • Gregor Mendel and his peas… • Austrian Priest and teacher who tended the gardens. • Experimented with pea plants • Observed how traits are inherited, what traits were passed from parents to offspring.

  4. Mendel’s experiment • Mendel crossed many different traits in pea plants and recorded his results. • He did 4 unique things in his experiment • Counted only one trait at a time • Used large numbers of data to off set chance • Did many identical experiments and combined results • Used probability to analyze results

  5. Mendel’s Experiment

  6. Vocabulary Assignment • Using your textbook (pgs 263- 274), define the following words. Find the definition from the chapter reading…not the glossary  Mendel Genetics Trait homozygous Hybrid heterozygous Gene phenotype Allele genotype Gamete incomplete dominance Codominance true-breeding (purebred)

  7. Genes vs. Alleles A gene is a section of DNA that forms a trait (protein). For example: Hair color, Height, ear lobes…. Alleles are different forms of a gene. For example: brown hair, blonde hair or Tall and short. You get one allele for each trait from your parents…

  8. How do we figure out which alleles win? • You get one allele from each of your parents in the egg and sperm. • Dominant allele – the allele that “wins”. We use a capital letter “R” • Recessive allele – the allele that is hidden or loses . We use a lower case letter “r”.

  9. Let’s do an example • Lets pretend that… R = can roll their tongue r = can’t roll their tongue • RR = Dominant, Dominant - Homozygous This person can roll their tongue • Rr = Dominant, recessive – Heterozygous (hybrid) • This person can roll their tongue • rr = recessive, recessive - Homozygous • This person can’t roll their tongue

  10. So the basics … • Each gamete (sperm or egg) cell has one allele for a trait. • When they fertilize, the two alleles are joined – (remember most basic traits need two alleles) • The dominant alleles will always be expressed • If there are two recessive alleles, then the recessive form of the trait will be expressed.

  11. 1-Trait Punnett SquaresThey show the possible outcomes of crosses.

  12. Punnett Square Vocabulary • On your Punnett Square, the letters (alleles) are called the Genotype. • Example: RR, Rr, rr • The Phenotype is what the physical trait actually looks like (words) • Example: can roll tongue, blond hair, blue eyes, etc.

  13. To begin a Punnett Square 4 steps • Make a box • Put the genotypes of the parents on the outside. Example: Cross Tt x tt

  14. Punnett Squares cont’d. Steps, cont’d • Fill in the box • Figure out the genotype and phenotype of the offspring. *Show as a percent or fraction Genotype - letters TT 0% Tt 50% tt 50% Phenotype - appearance 50% Can Roll tongue 50% Can’t Roll Tongue T t tt Tt Tt tt tt

  15. Practice Problem #2 – Word Problem • B = Brown Hair • b = blonde hair • Cross a homozygous brown haired man with a heterozygous brown haired female. What are the genotypes and phenotypes of their possible offspring? Genotype: BB = Bb = bb = Phenotype Brown hair = blond hair =

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