The document discusses genetic linkage, explaining the association of genes on the same chromosome and its impact on inheritance patterns. It details complete and incomplete linkage, emphasizing that linked genes tend to be inherited together unless crossing over occurs. Additionally, it describes two-point and three-point crosses as methods to analyze genetic relationships and determine gene order in organisms.

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

7. 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.

8. 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.

9. 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.

10. • 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