genetics topic on two factor cross and three factor cross

for education purpose for student

1. TWO FACTOR CROSS AND THREE FACTOR CROSS

2. LINKAGE Linkage is the close association or other DNA sequences on the same chromosome. The closer two gene are to each other on the chromosome ,the greater the probability that they will be inherited together.

3. LINKAGE TYPES COMPLETE LINKAGE The genes located on the same chromosome do not separate and are inherited togeather over the generation due to the absence of crossing over. Complete linkage allows the combination of parental traits to be inherited as such. It is rare but has been reported in male drosophila and some other heterogametic organisms.

4. Genes present in the same chromosome have a tendency to separate due to crossing over and hence produce recombinant progeny besides the parental type. The number of recombinant individuals is usually less than the number expected in independent assortment. INCOMPLETE LINKAGE

5. COMPLETE LINKAGE INCOMPLETE LINKAGE NO LINKAGE LINKAGE TYPE

6. LINKAGE GROUP A Linkage group is a linearly arranged group of linked genes which are normally inherited together except for crossing over. Linkage group, in genetics ,all of the genes on a single chromosome. They are inherited as a group; that is during cell division they act and move as a unit rather than independently.

7. TWO POINT CROSS A two point test cross is done to determine the recombinant frequency between two linked genes. The classic mendelian dihybrid cross ratio(round yellow and green wrinkled seeds) is 1:1:1:1, which shows that genes are not linked and located on different chromosomes.

8. THREE POINT CROSS A three point cross is used to determine the loci of three genes in an organism’s genome. Important for order of gene and gene mapping.

9. There are three genes a,b,c percentage of crossing over between a and b is 20%, b and c is 28% and a and c is 8%. What is the sequence of genes on chromosome? A : b,a,c B : a,b,c C : a,c,b D : none of the above