The use of nucleotide sequence data to measure genetic variability is complicated by the fact that the genes of many eukaryotes are complex in organization and contain 5' and 3' flanking regions as well as introns. Researchers have compared the nucleotide sequence of two cloned alleles of the γ-globin gene from a single individual and found a variation of 1 percent. Those differences include 13 substitutions of one nucleotide for another and three short DNA segments that have been inserted in one allele or deleted in the other. None of the changes takes place in the gene's exons (coding regions). Why do you think this is so, and should it change our concept of genetic variation?
Table of contents
- 1. Introduction to Genetics51m
- 2. Mendel's Laws of Inheritance3h 37m
- 3. Extensions to Mendelian Inheritance2h 41m
- 4. Genetic Mapping and Linkage2h 28m
- 5. Genetics of Bacteria and Viruses1h 21m
- 6. Chromosomal Variation1h 48m
- 7. DNA and Chromosome Structure56m
- 8. DNA Replication1h 10m
- 9. Mitosis and Meiosis1h 34m
- 10. Transcription1h 0m
- 11. Translation58m
- 12. Gene Regulation in Prokaryotes1h 19m
- 13. Gene Regulation in Eukaryotes44m
- 14. Genetic Control of Development44m
- 15. Genomes and Genomics1h 50m
- 16. Transposable Elements47m
- 17. Mutation, Repair, and Recombination1h 6m
- 18. Molecular Genetic Tools19m
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
20. Quantitative Genetics
Traits and Variance
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Join thousands of students who trust us to help them ace their exams!Watch the first videoMultiple Choice
A trait controlled through polygenic inheritance was observed in a series of experiments. A brown eyed rabbit was mated with a blue eyed rabbit. 130 F2 offspring were produced. 2 offspring had brown eyes and 2 offspring had blue eyes. How many polygenes control eye color in rabbits?
A
1
B
2
C
3
D
4

1
Understand that polygenic inheritance involves multiple genes (polygenes) contributing to a single trait, such as eye color in rabbits.
Recognize that the distribution of phenotypes in the F2 generation can provide clues about the number of polygenes involved. In this case, the extreme phenotypes (brown and blue eyes) are rare.
Recall that the number of phenotypic classes in polygenic inheritance is given by the formula: number of phenotypic classes = 2n + 1, where n is the number of polygenes.
Given that there are 2 offspring with brown eyes and 2 with blue eyes, these represent the extreme phenotypes. The rest of the offspring will have intermediate eye colors.
Use the formula to determine the number of polygenes: if there are 2 extreme phenotypes, then 2n + 1 = 5 phenotypic classes, which implies n = 2. Therefore, 3 polygenes control the eye color in rabbits.
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