1 / 15

Mendelian Genetics

BSC 2010L. Mendelian Genetics. Human Chromosomes. Humans have 46 chromosomes, 23 homologous pairs Remember that the # of chromosomes differs for different species When looking at each pair of homologous chromosomes: 1 came from mom, one came from dad

Télécharger la présentation

Mendelian Genetics

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. BSC 2010L Mendelian Genetics

  2. Human Chromosomes • Humans have 46 chromosomes, 23 homologous pairs • Remember that the # of chromosomes differs for different species • When looking at each pair of homologous chromosomes: • 1 came from mom, one came from dad • Each contains the same genes, however an individual can have 2 alternate forms of that gene (alleles)

  3. Alleles • Alleles can be dominant or recessive • Let’s look at eye color • Brown eyes are dominant – B • Blue eyes are recessive – b • Homozygous – having the same alleles • BB or bb • Heterozygous – having different alleles • Bb • Genotype vs Phenotype • Genotype – what alleles does that person have for that gene? • BB or bb or Bb • Phenotype – refers to an individual’s appearance, what is their eye color? • BB or Bb – Brown eyes • bb – blue eyes

  4. Law of Segregation • Each organism contains 2 alleles for each trait, and the alleles segregate during the formation of gametes. Each gamete then contains only 1 allele for each trait. When fertilization occurs, the new organism has 2 alleles for each trait, one from each parent • This is why it is important that 1 of each homologous pair of chromosomes ends up in the gamete at the end of meiosis

  5. Monohybrid cross • Eye color • Bb x Bb (what is the eye color of both these parents?) • Gametes of both these parents: • Looking at the Punnett Square below, these parents have a 75% chance of having a brown eyed child and 25% chance of having a blue eyed child • Genotypic Ratio – 1: 2: 1 (BB:Bb:bb) • Phenotypic Ratio – 3:1 (brown:blue)

  6. Dihybrid Cross • Let’s look at corn • P = purple kernel • p= yellow kernel • S = smooth • s = wrinkled kernel • Think of each kernel as being an individual offspring

  7. Dihybrid Cross • PpSs x PpSs • What are the gametes of these 2 individuals? Remember, one of each letter MUST be in each gamete • Now let’s do a Punnett Square

  8. Dihybrid Cross • Resulting possible offspring: • 9 – purple, smooth • 3 – purple, wrinkled • 3 – yellow, smooth • 1 – yellow wrinkled • = 16 possibilities (count # of boxes in cross) • Dihybrid cross between 2 heterozygous individuals results in a 9:3:3:1 phenotypic ratio

  9. Chi-Square Analysis • When doing these Punnett Squares, will data obtained from sample always follow the calculated ratios? • NO! These are predictions. However, looking at a larger population, one can test and see if deviations from the expected values are just due to chance • We do that by using a statistical tool such as the Chi-Square

  10. Before we go on: • Chi-Square versus Punnett Square • Don’t get these confused!!!! • Punnett squares are actual squares that we use to help us match up chromosomes that are in gametes • Chi-Square • Statistical test – the number is referred to as “x2=“

  11. Chi-Square Analysis • Let’s look at the dihybrid cross we did with the peas a couple of slides back • We expect a 9:3:3:1 ratio • We take an ear of corn and count: • 201 purple, smooth • 70 purple, wrinkled • 89 yellow, smooth • 22 yellow, wrinkled

  12. Chi-Square Analysis • X2 = 5.289 • C-1=3 (# of phenotypes-1, 4-1=3) • Scan across row 3 • p value for x2 value of 5.289 falls between 0.20 and 0.10 • Hypothesis is supported • Our sample fit 9:3:3:1 ratio, differences are due to just random chance

  13. X-linked crosses • With the sex chromosomes, some alleles only occur on the X chromosome • Therefore, males with a recessive gene on their X chromosome will express that trait • Let’s take a look at hemophilia: • XhX x XY

  14. X-linked Crosses • This couple has the following chances with their offspring: • 50% chance girl, 50% boy • 75 % chance of having child with no hemophilia • 25% chance of having boy with hemophilia • 25% chance of having girl who is carrier of hemophilia

  15. Today’s Lab • Continue looking at slides of mitosis and meiosis under microscope from last week • Continue looking at models of mitosis and meiosis • Practice Punnett squares • Observe corn examples • Monohybrid cross • Dihybrid cross • Perform Chi-Square analysis using corn examples

More Related