Length variation in mitochondrial DNA of the minnow Cyprinella spiloptera.

Abstract Length differences in animal mitochondrial DNA (mtDNA) are common, frequently due to variation in copy number of direct tandem duplications. While such duplications appear to form without great difficulty in some taxonomic groups, they appear to be relatively short-lived, as typical duplication products are geographically restricted within species and infrequently shared among species. To better understand such length variation, we have studied a tandem and direct duplication of approximately 260 bp in the control region of the cyprinid fish, Cyprinella spiloptera. Restriction site analysis of 38 individuals was used to characterize population structure and the distribution of variation in repeat copy number. This revealed two length variants, including individuals with two or three copies of the repeat, and little geographic structure among populations. No standard length (single copy) genomes were found and heteroplasmy, a common feature of length variation in other taxa, was absent. Nucleotide sequence of tandem duplications and flanking regions localized duplication junctions in the phenylalanine tRNA and near the origin of replication. The locations of these junctions and the stability of folded repeat copies support the hypothesized importance of secondary structures in models of duplication formation.

Download Full-text

Mitochondrial DNA length variation and heteroplasmy in populations of white sturgeon (Acipenser transmontanus).

Genetics ◽

10.1093/genetics/132.1.221 ◽

1992 ◽

Vol 132 (1) ◽

pp. 221-228 ◽

Cited By ~ 6

Author(s):

J R Brown ◽

A T Beckenbach ◽

M J Smith

Keyword(s):

Copy Number ◽

Single Copy ◽

Repeat Sequence ◽

White Sturgeon ◽

Acipenser Transmontanus ◽

Length Variation ◽

Chi Square ◽

Mutation Pressure ◽

Frequency Distributions ◽

D Loop

Abstract Southern blot analysis was used to quantify the extent of mtDNA D-loop length variation in two populations of white sturgeon, Acipenser transmontanus. Over 42% of individuals were heteroplasmic for up to six different mtDNA length variants attributable to varying copy numbers of an 82-bp repeat sequence. Chi-square analyses revealed that the frequencies of length genotypes and the incidence of heteroplasmy were significantly different between Fraser and Columbia River sturgeon populations but not between restriction site haplotypes. Heteroplasmic fish have, on average, higher copy number than homoplasmic fish. Forty-five of 101 homoplasmic individuals carry only a single copy of the repeat, while none of the 73 heteroplasmic fish has the single repeat as the predominant variant. On the basis of differences in frequency distributions of copy number within and between fish, we suggest that (1) heteroplasmy is maintained by high recurrent mutation of multiple copy genomes, favoring increased copy number and (2) the mutation pressure toward higher copy number heteroplasmy is partially offset by selection to reduced genome size and segregation to the homoplasmic condition.

Download Full-text

Heteroplasmy of short tandem repeats in mitochondrial DNA of Atlantic cod, Gadus morhua.

Genetics ◽

10.1093/genetics/132.1.211 ◽

1992 ◽

Vol 132 (1) ◽

pp. 211-220 ◽

Cited By ~ 2

Author(s):

E Arnason ◽

D M Rand

Keyword(s):

Mitochondrial Dna ◽

Copy Number ◽

Gadus Morhua ◽

Tandem Repeats ◽

Atlantic Cod ◽

Length Variation ◽

The North ◽

Loop Region ◽

D Loop ◽

Displacement Model

Abstract The mitochondrial DNA of the Atlantic cod (Gadus morhua) contains a tandem array of 40-bp repeats in the D-loop region of the molecule. Variation among molecules in the copy number of these repeats results in mtDNA length variation and heteroplasmy (the presence of more than one form of mtDNA in an individual). In a sample of fish collected from different localities around Iceland and off George's Bank, each individual was heteroplasmic for two or more mtDNAs ranging in repeat copy number from two (common) to six (rare). An earlier report on mtDNA heteroplasmy in sturgeon (Acipenser transmontanus) presented a competitive displacement model for length mutations in mtDNAs containing tandem arrays and the cod data deviate from this model. Depending on the nature of putative secondary structures and the location of D-loop strand termination, additional mechanisms of length mutation may be needed to explain the range of mtDNA length variants maintained in these populations. The balance between genetic drift and mutation in maintaining this length polymorphism is estimated through a hierarchical analysis of diversity of mtDNA length variation in the Iceland samples. Eighty percent of the diversity lies within individuals, 8% among individuals and 12% among localities. An estimate of theta = 2N(eo) mu greater than 1 indicates that this system is characterized by a high mutation rate and is governed primarily by deterministic dynamics. The sequences of repeat arrays from fish collected in Norway, Iceland and George's Bank show no nucleotide variation suggesting that there is very little substructuring to the North Atlantic cod population.

Download Full-text