HWK answers

3.4: continued…. Genetic diseases & mutations

Mendel & his Pea’s… The significance of his work was not realised until after his death He is now known as ‘the father of modern genetics’ The law of independent assortment which states: “allele pairs separate during the formation of gametes” (think – random orientation of chromosomes during meiosis)

Try these! Mendel-and-pea-plants.html Mendel-and-pea-plants.html ndel.html ndel.html

Dihybrid crosses Mendel experimented with these traits in his pea experiments: -Seed shape -Seed colour True breeding = homozygous for desired trait. R = round peas r = wrinkled peas Y = yellow peas y = green peas Complete the following table to show the genotypes: Parents phenotypesRound yellowGreen wrinkled Parents genotypesRRYYrryy Parent gametesRYry F 1 genotypesRrYy F 1 phenotypeRound yellow Dihybrid cross determines the allele combinations for two genes that are unlinked (not on the same chromosomes). There are two genes, two alleles for each gene.

RYRyrYry RYRRYYRRYyRrYYRrYy RyRRYyRRyyRrYyRryy rYRrYYRrYyrrYYrrYy ryRrYyRryyrrYyrryy Round yellow peas x9 Round green peas x3 Wrinkled yellow peas x3 Wrinkled green peas x1 Mendels conclusions from his pea experiments were very close to these theoretical probabilities. This is unusual.

Statisticians are convinced that Mendel’s results are too close to exact ratios to be genuine. We shall never know how this came about, but it offers an opportunity to discuss the need for scientists to be truthful about their results, whether it is right to discard results that do not fit a theory as Louis Pasteur is known to have done, and the danger of publishing results only when they show statistically significant differences. TOK: Reasons for Mendel’s theories not being accepted by the scientific community for a long time could be considered. Other cases of paradigm shifts taking a long time to be accepted could be considered. Ways in which individual scientists are most likely to be able to convince the scientific community could be considered, and also the need always to consider the evidence rather than the views of individual scientists, however distinguished.

How many genetic disorders do you think have been identified so far…. ◦ Examples include:  Cystic fibrosis  Sickle cell anaemia  Hemophillia  Huntington’s  Tay-Sachs disease (progressive neurological disease)  Marfan’s Syndrome (proteins in connective tissue do not form properly, results in many problems throughout the body – heart values particularly vulnerable)

Mutations Defined as “a random change to the base sequence of a gene” 1. Radiation can cause changes in the chemical structure of DNA (gamma rays, alpha particles, radioactive isotopes, short wave UV radiation & x-rays) 2. Chemical substances can also cause a change in the chemical structure of DNA (benzo(a)pyrene, nitrosamines – tobacco, mustard gas)

Research paper Max. 500 words, correctly cited. A response to the statement from the syllabus: ◦ “Consequences of radiation after nuclear bombing of Hiroshima and Nagasaki and nuclear accidents at Chernobyl”