Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
Chapter 6: Genetic linkage and mapping in eukaryotes
1
, Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
- Each chromosome carries hundreds – thousands different genes
- Data from genetic crosses are used to construct a genetic map shows the order of
genes along a chromosome
6.1: Overview of linkage
- Synteny = the situation in which two or more genes are located on the same
chromosome
- Genetic linkage = the phenomenon is which genes that are close together on the same
chromosome tend to be transmitted as a unit
- Chromosomes are sometimes called linkage groups group of genes that are linked
together
o Number of linkage groups = number of chromosome types
- Two-factor cross = two different characters in a cross
- Three-factor cross = three different characters in a cross
Bateson and Punnett discovered two genes that did not assort
independently
- Mendel, two-factor cross: 9:3:3:1
- Not this ratio in a cross of sweet peas involving the characters color
and shape
o The F2 generation had a greater proportion of the two
phenotypes found in the P generation they suggested that
the transmission was coupled, the alleles were not assorted
independently
6.2: Relationship between linkage and crossing over
- Crossing over: homologous chromosomes can exchange pieces
with each other the linkage can be altered during meiosis
- the sister chromatids associate with the homologous sister chromatids to form a bivalent
composed of two pairs of sister chromatids in prophase 1 of meiosis 1 crossing
over may occur between sister chromatids of a homologous pair
Crossing over may produce recombinant genotypes
- Figure a: no crossing over occurred
- Figure b: crossing over occurs recombinant cells =
haploid cells after crossing over produce recombinant
offspring
- Nonrecombinant offspring with the same combination of
alleles found in the parental chromosomes
- Genetic recombination when offspring inherit a combination
of two or more alleles or traits that are different from either of
their parents
o Two/more genes are linked, crossing over during
meiosis
o Two/more genes on different chromosomes,
independent assortment
- Recombinant offspring are produced by crossing over
between two homologous chromosomes during meiosis in a
parent, leading to a different combination of alleles along a
chromosome compared to that parent
2
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
Chapter 6: Genetic linkage and mapping in eukaryotes
1
, Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
- Each chromosome carries hundreds – thousands different genes
- Data from genetic crosses are used to construct a genetic map shows the order of
genes along a chromosome
6.1: Overview of linkage
- Synteny = the situation in which two or more genes are located on the same
chromosome
- Genetic linkage = the phenomenon is which genes that are close together on the same
chromosome tend to be transmitted as a unit
- Chromosomes are sometimes called linkage groups group of genes that are linked
together
o Number of linkage groups = number of chromosome types
- Two-factor cross = two different characters in a cross
- Three-factor cross = three different characters in a cross
Bateson and Punnett discovered two genes that did not assort
independently
- Mendel, two-factor cross: 9:3:3:1
- Not this ratio in a cross of sweet peas involving the characters color
and shape
o The F2 generation had a greater proportion of the two
phenotypes found in the P generation they suggested that
the transmission was coupled, the alleles were not assorted
independently
6.2: Relationship between linkage and crossing over
- Crossing over: homologous chromosomes can exchange pieces
with each other the linkage can be altered during meiosis
- the sister chromatids associate with the homologous sister chromatids to form a bivalent
composed of two pairs of sister chromatids in prophase 1 of meiosis 1 crossing
over may occur between sister chromatids of a homologous pair
Crossing over may produce recombinant genotypes
- Figure a: no crossing over occurred
- Figure b: crossing over occurs recombinant cells =
haploid cells after crossing over produce recombinant
offspring
- Nonrecombinant offspring with the same combination of
alleles found in the parental chromosomes
- Genetic recombination when offspring inherit a combination
of two or more alleles or traits that are different from either of
their parents
o Two/more genes are linked, crossing over during
meiosis
o Two/more genes on different chromosomes,
independent assortment
- Recombinant offspring are produced by crossing over
between two homologous chromosomes during meiosis in a
parent, leading to a different combination of alleles along a
chromosome compared to that parent
2
