2 Origin, Function, and Transmission of Accessory Chromosomes
MICHAEL HABIG
1
, EVA H. STUKENBROCK
1
CONTENTS
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
II. Accessory Chromosomes Are Widespread
and Diverse but Share Specific
Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
III. Fungal Accessory Chromosomes Are
Generally Associated with Function . . . . . . . . 30
IV. The Origin of Fungal Accessory
Chromosomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
V. Accessory Chromosomes Are Mitotically
Instable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
VI. Accessory Chromosomes Are Frequently
Transmitted in a Non-Mendelian Way During
Meiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
VII. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . 40
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
I. Introduction
Accessory chromosomes are found in some
but not all individuals of a population, in contrast to essential chromosomes that are always
present. This presence/absence polymorphism
of entire chromosomes was first observed in
1907 in a dipteran species using classical karyotyping (Wilson 1907). Since then accessory
chromosomes, also known as B, supernumerary, lineage-specific, or (conditionally) dispensable chromosomes, have been described
in a large variety of plant, animal, and fungal
species, including approximately 14% of karyotyped orthopteran insect species (Jones 1995)
as well as 8% of monocot and 3% of eudicot
species (Levin et al. 2005). Across this wide
range of taxa, accessory chromosomes share
the following defining characteristics: (i) they
are not essential for growth and development of
the organism, (ii) they do not recombine with
the essential chromosomes, and (iii) they often
do not follow Mendelian inheritance (Jones
1995). Historically, the amenability of some
accessory chromosomes in plants and animals
(called B chromosomes in these species) to light
microscopy allowed for earlier detection and
analysis in these kingdoms. In fungi however,
the relatively small size of accessory chromosomes hindered their detection using conventional light microscopy (Mehrabi et al. 2017).
The development of pulsed-field electrophoresis in 1984 (Schwartz and Cantor 1984) enabled
the separation of fungal chromosomes, and
with this technique the comparison of karyotypes between isolates led to the first discovery
of fungal accessory chromosomes in Nectria
haematococca in 1991 (Miao et al. 1991). The
advent of next-generation sequencing and
availability of whole genome sequences have
since then fueled detailed analyses including
population genomic analyses of accessory chromosomes (Plissonneau et al. 2018).
What is the origin of accessory chromosomes? Two non-exclusive models have been
proposed to explain their presence. They may
originate from essential core chromosomes and
diverge or degenerate over time (Galazka and
Freitag 2014), or they may be acquired by horizontal chromosome transfer (Mehrabi et al.
2011; Mehrabi et al. 2017). Both models are
supported by current data: in some species,
This chapter partly overlaps with a chapter in a thesis which
MH submitted to the Christian-Albrechts University of Kiel,
Germany, in order to obtain a PhD.
1 Environmental Genomics, Christian-Albrechts University of
Kiel and Max Planck Institute for Evolutionary Biology, Plo ¨n,
Germany; e-mail: mhabig@bot.uni-kiel.de; estukenbrock@bot.
uni-kiel.de
Genetics and Biotechnology, 3 rd Edition
The Mycota II
J.P. Benz, K. Schipper (Eds.)
© Springer Nature Switzerland AG 2020
MICHAEL HABIG
1
, EVA H. STUKENBROCK
1
CONTENTS
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
II. Accessory Chromosomes Are Widespread
and Diverse but Share Specific
Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
III. Fungal Accessory Chromosomes Are
Generally Associated with Function . . . . . . . . 30
IV. The Origin of Fungal Accessory
Chromosomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
V. Accessory Chromosomes Are Mitotically
Instable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
VI. Accessory Chromosomes Are Frequently
Transmitted in a Non-Mendelian Way During
Meiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
VII. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . 40
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
I. Introduction
Accessory chromosomes are found in some
but not all individuals of a population, in contrast to essential chromosomes that are always
present. This presence/absence polymorphism
of entire chromosomes was first observed in
1907 in a dipteran species using classical karyotyping (Wilson 1907). Since then accessory
chromosomes, also known as B, supernumerary, lineage-specific, or (conditionally) dispensable chromosomes, have been described
in a large variety of plant, animal, and fungal
species, including approximately 14% of karyotyped orthopteran insect species (Jones 1995)
as well as 8% of monocot and 3% of eudicot
species (Levin et al. 2005). Across this wide
range of taxa, accessory chromosomes share
the following defining characteristics: (i) they
are not essential for growth and development of
the organism, (ii) they do not recombine with
the essential chromosomes, and (iii) they often
do not follow Mendelian inheritance (Jones
1995). Historically, the amenability of some
accessory chromosomes in plants and animals
(called B chromosomes in these species) to light
microscopy allowed for earlier detection and
analysis in these kingdoms. In fungi however,
the relatively small size of accessory chromosomes hindered their detection using conventional light microscopy (Mehrabi et al. 2017).
The development of pulsed-field electrophoresis in 1984 (Schwartz and Cantor 1984) enabled
the separation of fungal chromosomes, and
with this technique the comparison of karyotypes between isolates led to the first discovery
of fungal accessory chromosomes in Nectria
haematococca in 1991 (Miao et al. 1991). The
advent of next-generation sequencing and
availability of whole genome sequences have
since then fueled detailed analyses including
population genomic analyses of accessory chromosomes (Plissonneau et al. 2018).
What is the origin of accessory chromosomes? Two non-exclusive models have been
proposed to explain their presence. They may
originate from essential core chromosomes and
diverge or degenerate over time (Galazka and
Freitag 2014), or they may be acquired by horizontal chromosome transfer (Mehrabi et al.
2011; Mehrabi et al. 2017). Both models are
supported by current data: in some species,
This chapter partly overlaps with a chapter in a thesis which
MH submitted to the Christian-Albrechts University of Kiel,
Germany, in order to obtain a PhD.
1 Environmental Genomics, Christian-Albrechts University of
Kiel and Max Planck Institute for Evolutionary Biology, Plo ¨n,
Germany; e-mail: mhabig@bot.uni-kiel.de; estukenbrock@bot.
uni-kiel.de
Genetics and Biotechnology, 3 rd Edition
The Mycota II
J.P. Benz, K. Schipper (Eds.)
© Springer Nature Switzerland AG 2020