LESSON 4 GENETICS
Background Linkage and recombination
determines the phenomenon of
T.H.Morgan and A.H. Sturtevant
inheritance of genes
worked on fruit flies
Linkage
suggested that the genes are
tendency of genes present in the
coupled or linked if they were
chromosome to stay intact and
present on the same chromosome
transfer to the next generation
Genes close together in a whereas crossing over is the
chromosome, the stronger the exchange of chromosomal
linkage sections to disrupt built links and
form new linkages.
Linkage and recombination
Linkages generate parental
describe the inheritance of genes
types and increases in age as the
2 or more genes linked together are linkage increases.
always inherited together in the
Crossing over generates
same combination for more than
recombination and it decreases
two generations
with age. The occurrence of
Recombination crossing over between two
genes is decreased if they are
the genetic material is
placed closely, whereas the
exchanged b/w different
linkage strength between two
organisms leads to
genes increases if a chromosome
production of offspring with
is located in the vicinity.
the combination of traits
Linkages assist in maintaining a
Definition
newly improved variety, crossing
Linkage over, on the other hand, forms
physical connection of genes as a source of variations to
Genes on same chromosomes produce new varieties.
are linked genes
Difference b/w crossing over and linkage
Tendency of genes of same
chromosome to remain together
Link can be broken by
recombination b/w genes
Mechanism of recombination is
crossover
Occurs b/w homologous
chromosomes during meiosis
,LESSON 4 GENETICS
genes found on different
chromosomes or gene far
apart on the same
chromosome, assort
independently
Assortment
when genes go into gametes
the allele received for one
gen doesn’t affect the allele
received for the other, due
Linkage
to random orientation of
presence in the same homologous chromosome
chromosome close non allelic pair during meiosis
genes affecting two traits Linkage group
genes close to each other on
In LIA dihybrid
a chromosomes and tend to
4 gametes production(ex. be transmitted together, n
AaBb- double heterozygous
Linkage group
hybrids)
Genes that are present on a
Gametes
homologous pair of chromosomes
AB,Ab,aB,ab are known as linkage groups and
they inherit together except for
Inheritance of traits in a pattern that
crossing over.
violates Mendel’s principle of LIA
The number of linkage groups
Non allelic genes
present in an organism corresponds
two different genes, different to the haploid number of
loci chromosomes in the organism.
Allelic genes Example:
same letter, same loci Drosophila melanogaster
consists of 4 pairs of
Analogy :
chromosomes and thus has 4
Close relationship rather than in LDR linkage groups.
Linked genes near to each other in
Linkage group in Man
same chromosome, alleles or gene
versions already together on one Linkage group
chromosome will be inherited as a
the set of all the gene that
unit more frequently than not
are present together and
Unlinked genes
, LESSON 4 GENETICS
one located on a single Makes genes on same
chromosome chromosome but very far apart
assort independently and
Total number of probable linkage
gamete types are in 25%
groups in organism is the total
frequency
number of chromosome pairs
present in an individual
Males
22 autosomes + X&Y = 24
linkage groups
Females
22 autosomes + 1X pair = 23
linkage groups
Homologous chromosomes
Crossing over in very close genes?
Very close genes on same
chromosomes still undergo crossing
over but different gamete types
produced
Crossing over
Instead of independent assortment,
is the exchange of segments genes tend to stick together during
observed in homologous meiosis
chromosomes between non-
Alleles of the genes already together
sister chromatids
on a chromosome will tend to be
takes place during the passed as a unit to gametes
pachytene stage of the prophase
Crossing over
I in the cell division process of
meiosis and always takes place
within linked genes.
The recombination of linked
genes that crossing over
produces plays a significant role
in evolution.
Background Linkage and recombination
determines the phenomenon of
T.H.Morgan and A.H. Sturtevant
inheritance of genes
worked on fruit flies
Linkage
suggested that the genes are
tendency of genes present in the
coupled or linked if they were
chromosome to stay intact and
present on the same chromosome
transfer to the next generation
Genes close together in a whereas crossing over is the
chromosome, the stronger the exchange of chromosomal
linkage sections to disrupt built links and
form new linkages.
Linkage and recombination
Linkages generate parental
describe the inheritance of genes
types and increases in age as the
2 or more genes linked together are linkage increases.
always inherited together in the
Crossing over generates
same combination for more than
recombination and it decreases
two generations
with age. The occurrence of
Recombination crossing over between two
genes is decreased if they are
the genetic material is
placed closely, whereas the
exchanged b/w different
linkage strength between two
organisms leads to
genes increases if a chromosome
production of offspring with
is located in the vicinity.
the combination of traits
Linkages assist in maintaining a
Definition
newly improved variety, crossing
Linkage over, on the other hand, forms
physical connection of genes as a source of variations to
Genes on same chromosomes produce new varieties.
are linked genes
Difference b/w crossing over and linkage
Tendency of genes of same
chromosome to remain together
Link can be broken by
recombination b/w genes
Mechanism of recombination is
crossover
Occurs b/w homologous
chromosomes during meiosis
,LESSON 4 GENETICS
genes found on different
chromosomes or gene far
apart on the same
chromosome, assort
independently
Assortment
when genes go into gametes
the allele received for one
gen doesn’t affect the allele
received for the other, due
Linkage
to random orientation of
presence in the same homologous chromosome
chromosome close non allelic pair during meiosis
genes affecting two traits Linkage group
genes close to each other on
In LIA dihybrid
a chromosomes and tend to
4 gametes production(ex. be transmitted together, n
AaBb- double heterozygous
Linkage group
hybrids)
Genes that are present on a
Gametes
homologous pair of chromosomes
AB,Ab,aB,ab are known as linkage groups and
they inherit together except for
Inheritance of traits in a pattern that
crossing over.
violates Mendel’s principle of LIA
The number of linkage groups
Non allelic genes
present in an organism corresponds
two different genes, different to the haploid number of
loci chromosomes in the organism.
Allelic genes Example:
same letter, same loci Drosophila melanogaster
consists of 4 pairs of
Analogy :
chromosomes and thus has 4
Close relationship rather than in LDR linkage groups.
Linked genes near to each other in
Linkage group in Man
same chromosome, alleles or gene
versions already together on one Linkage group
chromosome will be inherited as a
the set of all the gene that
unit more frequently than not
are present together and
Unlinked genes
, LESSON 4 GENETICS
one located on a single Makes genes on same
chromosome chromosome but very far apart
assort independently and
Total number of probable linkage
gamete types are in 25%
groups in organism is the total
frequency
number of chromosome pairs
present in an individual
Males
22 autosomes + X&Y = 24
linkage groups
Females
22 autosomes + 1X pair = 23
linkage groups
Homologous chromosomes
Crossing over in very close genes?
Very close genes on same
chromosomes still undergo crossing
over but different gamete types
produced
Crossing over
Instead of independent assortment,
is the exchange of segments genes tend to stick together during
observed in homologous meiosis
chromosomes between non-
Alleles of the genes already together
sister chromatids
on a chromosome will tend to be
takes place during the passed as a unit to gametes
pachytene stage of the prophase
Crossing over
I in the cell division process of
meiosis and always takes place
within linked genes.
The recombination of linked
genes that crossing over
produces plays a significant role
in evolution.
