This document discusses linkage mapping, which involves determining the relative positions of genes on chromosomes based on how often they are inherited together through analysis of recombination frequencies during meiosis. It provides background on the history of linkage mapping and definitions of key terms like linkage, linkage mapping, linkage groups, and types of linkage (complete and incomplete). Examples are also given to illustrate linkage analysis through test crosses and calculation of recombination frequencies.

1. Linkage mapping
By
Sneha sahu
botany msc. 1St semester
Sant gahira guru University ambikapur chhattisgarh India

2. Contant
. Introduction
. Definition
. History
. Linkage mapping
. Type of linkage
. Linkage group
. Examples .

3. Introduction
Linkage mapping the hereditary units or genes Which
determine the characters of an individual are carried in
the chromosome and on individual usually has many
genes for the determination of various different character

4. History of linkage mapping
Linkage maps were first developed by Alfred
Sturtevant , a student of Thomus Hunt Morgan. A
linkage map is a map based on the frequencies of
recombination between markers during crossover of
homologous chromosome

5. Definition
Linkage - type of coexistence of two or
More genes in the same cromosome is
known as linkage
Linkage mapping - A map of the genes on a
chromosome based on linkage analysis . A
linkage map does not show the physical
distances between genes but rather their
relative position, as determined by how
after two Gene loci are inherited together

6. Conti……
Numbers of recombination offspring
Map distance = -----------------------------------------------------
Total number of offspring
. Genes present in the chromosome can be
linked Or unlinked
. Unlinked genes are the genes which are
present in different non- homologous
chromosome
. During the gametes formation such genes
assort independently of each other
. When on the same cromosome, two or more
genes are present together, they are said to be
linked

7. Type…
(I) Complete linkage –
Where two or
more genes are completely linked and
there is no recombination or zero
percent of recombination is found , it
is termed as complete linkage.

8. Conti…
(ii) Incomplete linkage
When
two or more genes are present
in the se chromosome at some
distance. That the process of
crossing over can be carried out
giving gametes with both
parental and recombination
type the linkage is termed as
incomplete.

9. Conti……
Recombination frequency
number of recombination
Frequency of recombination = -------------------------------------- × 100
Total number of progeny

10. Linkage group
. Linkage Al the genes which are present On the same
chromosome are said To form one linkage group.
. The number of linkage group is equal to the number of
chromosome present in orgenism .
. For examples –
(I) In human male , there are ,22 pairs of autosomes , one X-
chromosome and one Y- chromosome , so the linkage
group will be 24.
(II) In human females , there are 22 pairs of autosomes and
2X- chromosomes , so the linkage group will be 23.

11. Example..
Two point cross
Que. True Breeding plant with violet and dull seed (WWSS) was
crossed with plant with white and shiny seeds ( wwss). The F1 offspring
( WwSs) were then test crossed to plants with white and shiny seeds (
wwss) . The offspring resulted from this cross is as follows .
On the basis of above data calculate the distance between the genes
S. No. Phenotype Numbers
1.
2.
Violet, dull seed (WwSs)
White , shiny seeds (wwss)
50
46
3.
4.
Violet, shiny seeds ( Wwss)
White , dull seeds ( wwSs)
12
10

12. Conti……