Originally Posted by Rox
I've been trying to get my head around this & my head is spinning
managed to get as far as understanding that a double haploid is a diploid as it carries 2 sets of chromosomes..Yeah? Or is a double haploid something else?
So if i am right, a diploid is identical to its parent? A haploid is a combination of both but not unique to either parent..
So if this diploid under goes Apomixis then..BINGO! Instant homozygous seeds...
I'm so excited at this prospect, assuming I have understood this correctly?
Anybody care to share some pictures?
So a double haploid IS a diploid BUT a diploid is not always a double haploid. Let me try to explain.... A pollen grain from the male plant is a haploid that carries 1/2 the chromosomes that will make up the final plant. The egg cell in the female has the other half of the chromosomes. We will focus on the male plant because generally double haploids are made from pollen grains.
Basic mendelian genetics says each gene has 2 possible alleles, a dominant and a recessive allele which segregate when the haploid cells are created. This means that each pollen grain contains either a dominant allele or a recessive allele. This is bad for breeders because it adds variability into their breeding program. Breeders want to know the exact alleles that are being crossed. Example: A plant with the genotype AaBbCcDd segregates into the following possible combinations of alleles in the pollen grains: AbCD, abcd, ABCD, aBCD, AbcD...... If you take one of these pollen grains (ABCD)and use it to make a double haploid then the genotype of the double haploid plant (diploid) is AABBCCDD. You take the chromosomes in the pollen grain and double them to create the proper number instead of fertilizing an egg cell. This is very good for breeders because then everytime this plant produces a seed it gives off a dominant allele and dominant alleles are generally good for yield and other traits.
So in the end... A double haploid has 2 identical sets of chromosomes and a normal diploid has 2 unique sets of chromosomes.
Hope this helps.