Genetics Experiments - Essay Example

Genetics In a mutant Jimson weed, chromosome B is present in three copies whereas all other chromosomes are in a diploid state. Jimson weed pollen grains do not tolerate multiple chromosomes and are incapable of fertilization (Crow and William 107). However, the ovum is capable of fertilization in the trisomic state. If you fertilize a trisomic Jimson weed plant, what zygotes would be formed? Tell which zygotes are diploid and which are trisomic. Assume that only the univalent mode occurs during meiosis; Let the trisomic genotype be p+p+p Male gametes P+ P+ P P+P+ P+P+P+ P+P+P+ P+P+P P+P P+PP+ P+PP+ P+PP P+P P+PP+ P+PP+ P+PP P+ P+P+ P+P+ P+P P+ P+P+ P+P+ P+P P PP+ P+P PP There are 9 diploid zygotes and 9 trisomic zygotes 2. Down syndrome can result from a Robertsonian translocation at a frequency of 9/100 live births. This type of Down’s syndrome usually occurs in mothers who are less than 30 years of age. The Robertsonian translocation that leads to Down syndrome occurs between chromosomes 21 and 14. During meiosis, three possible pairing configurations can be observed between the 14 and 21 translocate chromosome and normal homolog (Crow and William 111). Think about how there pairings might occur and draw all possible pairing arrangements. You should draw your pairing arrangements with respect to the equator of the cell at metaphas 3. Two closely related diploid species one with 2n = 44 chromosomes and the other with 2n = 38 chromosomes, mate a) What is the chromosome number in the allodiploid? (44 chromosomes + 38 chromosomes) / 2 = 41 b) What is the chromosome number in the allotetraploid? Chromosome number in allodiploid = 41 chromosomes Chromosome number in the allotetraploid c) Which of the two plants is sterile? 41 + 41 chromosomes = 81 chromosomes Allodiploid organisms are generally sterile thus an allodiploid plant is sterile 6. A species has 2n = 24. How many chromosomes will be found in all gametic cells produced in each of the following species variants? a. Hexaploid :- 2n = 24, n is therefore 12. Thus a hexaploid organism will have 12 * 6 = 72 chromosomes found in the gametic cells b. Autotetraploid :- 2n = 24, gametic chromosomes will be 2n + 2n + 2 n = 24 * 3 = 72 c. Octosonic : 2n – 8; 24 – 8 = 16 chromosomes d. Nullisomics :- 2n – 2; 24 – 2 = 20 chromosomes 7. Thinking about the concept of linkage ( true/false) a. Genes that are located close to each other and present on the same chromosome are linked – true b. Linkage can be demonstrated in a dihybrid testcross – true c. Linked genes behave as independently assorting genes during meiosis – false d. Linkage can be broken by the mechanisms of crossing over – true 8. Thinking about chromosomal abnormalities and inheritance (True/false) a. Chromosomal abnormalities usually result in genetically imbalanced gametes and zygotes – true b. Chromosomal abnormalities can affect either the number of chromosomes or the structure of the chromosomes but never both simultaneously – true c. Chromosomal abnormalities can result in change of gene order and expression d. Chromosomal abnormalities can result from exposure to radiation – true 9. what specific topic of introductory genetics fascinated you and motivated you to seek additional information Eukaryotic chromosome mapping This is because it helps us to determine whether genes are on the same or separate chromosomes. By calculating the frequency of crossing over, we obtain a measure of the map distance between the gene pairs (Crow and William 127). One genetic map unit (mu) is the distance between gene pairs for which one product of meiosis out of a hundred (100) is recombinant. If the distance between genes is 50 map units or more then the genes are found on different chromosomes thus being non linked loci. But if the distance between genes on a chromosome is less than 50 map units, then the genes are found on the same chromosome. 10. You performed the following crosses between plants with the following three flower color mutations. All mutations are recessive to the wild type blue flower color a) Name given to this type of genetic experiment/test – recombination to genes b) Number of genes that control the flower color – 2 genes 11. In the following test cross, genes a and b are 15 Cm apart; ab+/ a+b x ab/ ab Among 1000 progeny observed and counted: a. How many progeny are expected to be the result of a non cross 15/100 * 100 = 150 individuals b. How many homozygous recessive individuals were obtained ab+, ab, a+b+, a+b x ab F1 progeny - ab+/ab, ab/ab, a+b+/ab, a+b/ab ¼ * 1000 = 250 individuals 12. A chromosome has segments labeled below AB. CDEFG What types of chromosome abnormalities are required to alter the following chromosomes? a. ABB.EDCFG – interstitial inversion b. AB.VWXYZ – reciprocal translocation c. AB.CDG – terminal deletion d. C.BADEF – Inversion by loop formation 13. Explain how you would establish a genetic basis for this disease a. By DNA sequence technology b. If a base substitution mutation were the cause of Tangier disease, the base substitution would most likely result in a change to the tertiary structure of the protein (true/ false) true 14. Perform a crossover between homologues 2 and 3 at the point indicated in the diagram below. If a second crossover occurs in the same region between the 2 genes, tell which chromatids would be involved to produce the following outcomes a. 100 % recombinants – 1 and 3, 2 and 4 b. 0 % recombinants – 1 and 2, 3 and 4 15. Using the homologous chromosomes below, assume that a paracentric inversion occurs that involves genes B and C such that genes B and C are now inverted. The inversion occurs on only one homologue. During meiotic pairing of the inverted chromosome with the normal chromosome, a chiasma forms between B-C and crossing over follows a. What is the genotype with respect to all genes of the a centric chromosome after crossing over A CB BC b. What is the genotype of the dicentric chromosome after crossing over A C B Works Cited Crow, James F, and William F. Dove. Perspectives on Genetics: Anecdotal, Historical, and Critical Commentaries, 1987-1998. Madison [u.a.: University of Wisconsin Press, 2000. Print. Read More