Coconut is a highly heterozygous cross pollinated plant. Major mode of propagation is by seeds. On crossing of two genotypes, the next generation population may not show same character due to its heterozygosity. Then how different varieties are released (all propagated by seed) ?
Please check the following link and PDF attachments.
https://www.researchgate.net/publication/226298307_Coconut_Breeding
Let 'H' and 'h' be the genes that determine your term 'character'. If heterozygous plants (Hh) are crossed with themselves (i.e. Hh x Hh), they will produce half homozygous plants (i.e. 1 dominant HH and 1 recessive hh) and half heterozygous plants (i.e. 2 Hh). The resulting homozygous plants constitute stable varieties, so long as they are only bred with themselves (i.e. HH x HH or hh x hh) because they each have only one gene, respectively. But you would need to determine the genotype using a 'test cross' (see below). The hh varieties will have phenotypic traits not present in the heterozygous (Hh) or homozygous dominant (HH) plants.
How to do a test cross:
To identify whether an organism exhibiting a dominant trait is homozygous or heterozygous for a specific allele, a scientist can perform a test cross. The organism in question is crossed with an organism that is homozygous for the recessive trait (hh), and the offspring of the test cross are examined. If the test cross results in any recessive offspring (hh), then the parent organism is heterozygous for the allele in question (i.e. Hh). If the test cross results in ONLY phenotypically dominant offspring, then the parent organism is homozygous dominant for the allele in question (i.e. HH).
See this slide show of how to breed coconut: https://www.slideshare.net/pawannagar8/coconut-breeding
There are traditional breeding and biotechnology-assisted methods.
I think that Kapil Mohan Sharma is talking about the loss of some traits due to intercross between, for example, two varieties.
For example, varitey X has 3 important traits, controlled by allele A, B and C. And variety Y has 1 important trait controlled by allele D.
Lets say that a variety-X plant with genotypes AaBbCc(dd) cross to a variety-Y plant with aabbccDD, then the offspring plant with genotype, for example, aabbccDd will lose the 3 traits. And if the offspring plant genotype is AaBbccDd, then it lose 1 trait (cc).
But in the population form AaBbCc(dd) x aabbccDD cross, you can still get lines with 4 traits, the chance is 1/2 x 1/2 x 1/2 x 1 =1/8. If you breed variety X and 'fix' the genotypes first (AABBCC(dd)), then the chance to keep all 4 traits after cross to variety Y should be 100%.
Yes, that's another way of saying that only homozygous plants (i.e. AABBCCdd) will produce stable offspring, as I mentioned in my answer :)
Kindly suggest how to make an stable homozygous population from such a heterozygous population as mentioned by Yuan and Andrew. I need to do breeding in date palm where the plants are dioecious in nature where self crossing is not possible.
- Badges
- Science topic
- Similar topics
- Agricultural Science
- Agronomy