Crossing over, Concepts, Examples, Questions
- 2. CROSSING OVER Presented By: Muhammad Anas Rasool AGL-15-07 B.Sc. (Hons.) Agriculture College of Agriculture BZU Bahadur Sub Campus Layyah
- 3. What is crossing over..? • Crossing over, or recombination, is the exchange of chromosome segments between non-sister chromatids of homologous chromosomes in meiosis. • Crossing over creates new combinations of genes in the gametes , contributing to genetic diversity.
- 5. According to Mendel’s Laws: Allele pairs assort independently during gamete formation. Therefore, each gamete receives only one copy of an allele.
- 6. But when Genes are linked They are transmitted to offspring as they are present in parents.
- 8. 151+154 151+154+1195+1339 100 Recombination frequency (RF) = Recombinants Total offspring 100 10.7% = Recombination frequency (RF) = Let’s Find Recombinant Frequency
- 9. What does recombinant frequency mean…? • Recombinant Frequency (RF) means that how many new recombinants are formed in F2 & it represents that how far the two genes are located. • Higher the RF, more is the distance between both genes & vice versa. • If RF of two genes (present on the same chromosome) is 20% it means that the distance between them is 20 map units or 20 centimorgan. • Therefore, RF is useful for Gene Mapping.
- 10. BATESON & PUNNETT’s Experiment
- 12. 19+27 19+27+296+85 100 Recombination frequency (RF) = Recombinants Total offspring 100 10.7% = Recombination frequency (RF) = Recombinant Frequency
- 13. 0.1% frequency of recombination is observed in: a) Only in sex chromosomes b) Only in unlinked chromosomes c) In genes on two different chromosomes d) In genes located very close on same chromosome Now, it’s your turn…!
- 14. A scientist is studying two traits in a type of beetle: body texture and color. Smooth body (B) is dominant to rough body (b), and gray (G) is dominant to white (g). • A BbGg and a bbgg beetle mate and produce the following offspring: Phenotype Number of Offspring • Smooth, gray 345 • Rough, white 355 • Smooth, white 148 • Rough, gray 152 Now try to tell that either the genes B & G are linked or not…? Genes are linked (on the same chromosomes) but due to crossing over new recombinants (30 %) are formed…!
- 15. What is the distance between genes B & G that were discussed in last slide…?
- 16. THANK YOU