Free Response Slide 2 / 6 Calculated distances and percent - PowerPoint PPT Presentation

Slide 1 / 6 Free Response

Slide 2 / 6 Calculated distances and percent crossovers. Shaw, K. & Miko, I. (2008) Chromosome theory and the Castle and Morgan debate. Nature Education 1(1):142 1 If traits occur together 50% of the time, then they also occur apart 50% of the time. If traits occur together more often than they do separately, then they show crossing-over events less than 50% of the time, and the traits are predicted to be more closely associated on the chromosome. This crossing-over percentage is therefore a measure of their degree of linkage on the same chromosome. Specifically, for genes on the same chromosome, the following statements hold true: Crossing-over rate < 50% = Linkage (for genes and traits on same chromosome) Crossing-over rate = 50% = No linkage for genes and traits on separate chromosomes) A. H. Sturtevant, an undergraduate student working with Morgan, crossed Drosophila and looked at the linkage of 5 traits (P,R,M,C,O) around a single locus or trait B. The percent crossovers and calculated distance from B are shown in the above table. A Draw a plausible genetic map using the crossover percent data in above table. B Describe why these traits would not follow Mendelian phenotypic ratios between homozygous Parental genotypes or F1 generation crosses.

Slide 3 / 6 2 When Mendel crossed a pure breed Tall with a pure breed Short pea plant, the progeny was always Tall, but when he crossed the Tall progeny- he got a 3 Tall:1 Short ratio. For four hundred plants, the expected and observed numbers for a heterozygous cross is shown in the below table. Tall Short Expected 300 100 Observed 305 95 Lobo, I. (2008) Genetics and statistical analysis. Nature Education 1(1):109 Perform a Chi-square test for the above data. The null hypothesis for this test will be that observed data will differ A from the expected 3:1 Mendel ratios by chance at a significance level of 95%. Does your test confirms or rejects the null hypothesis? Show your calculations. B If you did a test cross with the parent generation and F1 generation, how would probabilities of the offspring differ?

Slide 4 / 6 http:/ / en.wikipedia.org/ wiki/ Mitochondrial_DNA Miko, I. (2008) Non- nuclear genes and their inheritance. Nature Education 1(1):135 Right: In humans, mitochondrial DNA is 3 the smallest chromosome, coding for 37 genes and containing approximately 16,600 base pairs. Most of the genes are involve in respiration or protein synthesis. In most species, including humans, mtDNA (mitochondrial DNA) is inherited solely from the mother. Left: Mitochondria that have wild-type mtDNA are shown in red (lighter shade); those having mutant mtDNA are shown in blue (darker shade). In a heterozygous population of cells or tissue, how would the distribution of mutant alleles present in the mitochondrial DNA differ from the distribution of mutant A alleles present in chromosomal DNA? Would how the distribution of mutations in mtDNA be B affected in mitosis versus meiosis?

Slide 5 / 6 4 In 1909, not long after Mendel's principles of inheritance became well accepted, Carl Correns noticed some strange patterns of inheritance in four-o'clock plants, Mirabilis jalapa. He crossed female plants (seed) of three different phenotypes with male plants (pollen) having the same three phenotypes: white, green, and variegated stem and leave colors. Correns’s results are shown in the table below. Miko, I. (2008) Non-nuclear genes and their inheritance. Nature Education 1(1):135 A Identify the dominant phenotype, and describe whether or not the sex of the plant matters. B How do Correns’s results differ from the expected Mendelian patterns of inheritance?

Slide 6 / 6 5 Microsatellites are repeated sequences that usually consist of two, three or four nucleotides (di-, tri-, and tetranucleotide repeats respectively), and can be repeated 3 to 100 times, with the longer loci generally having more alleles due to the greater potential for slippage, a type of replication error. Microsatellites, such as CA nucleotide repeats, are very frequent in human and other genomes and can be present every few thousand base pairs. If human DNA is cut with one or more enzymes, the fragments will be of varying lengths for individuals; therefore, theses difference to can be used to identify a specific person with near perfect accuracy. The diagram below shows an electronic readout for the electrophoresis of DNA fragments from a potential father, mother, and child. The numbered peaks represent specific DNA fragments that are specific to the respective individual. Adams, J. (2008) Paternity testing: blood types and DNA. Nature Education 1(1):146 A How do you know the child is the son of this father and mother? Using the following chromosome representations or models, show how meiosis would produce the gametes B that through fertilization generated the genetic combination seen in the DNA electrophoregram. 6 9.3 9 7