Estudo da herança e manutenção de cromossomos B em Astyanax paranae através de cruzamentos dirigidos
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Data
2019-07-10
Autores
Goes, Caio Augusto Gomes
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Universidade Estadual Paulista (Unesp)
Resumo
A ictiofauna neotropical é uma das mais ricas do mundo, sendo estimada a ocorrência de 9100 espécies de peixes. Dentre estes, o gênero Astyanax (Characiformes, Characidae) se destaca como um dos mais abundantes em espécies, sendo marcante a presença de cromossomos B neste grupo. Cromossomos B, ou supranumerários, são cromossomos adicionais aos cromossomos padrões do organismo e considerados dispensáveis. A origem destes cromossomos ainda é incerta, sendo os modelos mais aceitos a origem intraespecífica, em que os cromossomos B se originam dos próprios cromossomos da espécie e a origem interespecífica, em que os supranumerários se originariam dos cromossomos de outra espécie próxima através da hibridação. Uma das características que definem os cromossomos B é a sua transmissão que foge dos padrões mendelianos, levando a acumulação ou extinção destes elementos. Em peixes, cromossomos B estão presentes em 113 espécies, sendo a variante presente em Astyanax paranae um dos modelos de estudo para o grupo. Esta variante foi diagnosticada como um isocromossomo de origem intraespecífica, e sequencias presentes neste cromossomo também estão presentes nos cromossomos B de outras espécies do grupo, sugerindo uma origem comum. Entretanto, dados em relação à transmissão deste supranumerário ainda não são conhecidos. Diante disto, o objetivo do presente trabalho foi descrever o padrão de transmissão do cromossomo B presente em A. paranae através de cruzamentos dirigidos. A transmissão de cromossomos supranumerários revelou ser dependente do sexo do portador nesta população, sendo o índice de transmissão (kb) de 0,439 em cruzamentos onde somente o macho possui cromossomo B; 0,107 em cruzamentos onde apenas a fêmea é portadora de cromossomo B e 0,356 em cruzamentos onde ambos os parentais possuíam supranumerários. Conclui-se que a herdabilidade da variante de cromossomos supranumerários presente na população de A. paranae é diretamente dependente do sexo do parental portador, com transmissão neutra pelos machos e eliminação pelas fêmeas na população estudada.
The neotropical ichthyofauna is one of the richest in the world, estimated in 9100 fish species. In this group, the genus Astyanax (Characiformes, Characidae) is considered one of the most abundant in species, being remarkable the presence of supernumerary or B chromosomes in the group. B chromosomes are additional chromosomes to the standard chromosomes and are considered dispensable. These elements are present in plants, animals and fungi and are generally formed by repetitive DNA sequences and fragments of ribosomal and histone genes. The origin of these chromosomes is still uncertain, and the most accepted model intraspecificrelated, where the B chromosomes arise from the same chromosomes of the species and the intraspecific origin, although the supernumerary ones would originate from the chromosomes of another related species by hybridization. One of the important characteristics of B chromosomes is related with their transmission, which does not follow Mendelian patterns, leading to the accumulation or extinction of these elements. In fish, B chromosomes are present in 113 species, and the variant present in Astyanax paranae is one of the studing models for the group. This variant was diagnosed as an isochromosome of intraspecific origin, and sequences present on this chromosome are also present on the B chromosomes of other related species, suggesting a common origin. However, data regarding the transmission of this supernumerary are still unknown. Therefore, the objective of the present work was to describe the transmission pattern of the B chromosome present in A. paranae through directed crosses by in vitro fertilization. Transmission of supernumerary chromosomes revealed be dependent on the carrier’s gender, with a transmission rate (kb) of 0.439 in crosses where only the male has a B chromosome; 0.107 at crosses where only the female carries the B chromosome and 0.356 at crosses where both parents had supernumerary. It is concluded that the inheritance of the supernumerary chromosomal variant present in the A. paranae population is directly dependent on the sex of the parental carrier, with neutral transmission by males and elimination by females in the studied population.
The neotropical ichthyofauna is one of the richest in the world, estimated in 9100 fish species. In this group, the genus Astyanax (Characiformes, Characidae) is considered one of the most abundant in species, being remarkable the presence of supernumerary or B chromosomes in the group. B chromosomes are additional chromosomes to the standard chromosomes and are considered dispensable. These elements are present in plants, animals and fungi and are generally formed by repetitive DNA sequences and fragments of ribosomal and histone genes. The origin of these chromosomes is still uncertain, and the most accepted model intraspecificrelated, where the B chromosomes arise from the same chromosomes of the species and the intraspecific origin, although the supernumerary ones would originate from the chromosomes of another related species by hybridization. One of the important characteristics of B chromosomes is related with their transmission, which does not follow Mendelian patterns, leading to the accumulation or extinction of these elements. In fish, B chromosomes are present in 113 species, and the variant present in Astyanax paranae is one of the studing models for the group. This variant was diagnosed as an isochromosome of intraspecific origin, and sequences present on this chromosome are also present on the B chromosomes of other related species, suggesting a common origin. However, data regarding the transmission of this supernumerary are still unknown. Therefore, the objective of the present work was to describe the transmission pattern of the B chromosome present in A. paranae through directed crosses by in vitro fertilization. Transmission of supernumerary chromosomes revealed be dependent on the carrier’s gender, with a transmission rate (kb) of 0.439 in crosses where only the male has a B chromosome; 0.107 at crosses where only the female carries the B chromosome and 0.356 at crosses where both parents had supernumerary. It is concluded that the inheritance of the supernumerary chromosomal variant present in the A. paranae population is directly dependent on the sex of the parental carrier, with neutral transmission by males and elimination by females in the studied population.
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Palavras-chave
Astyanax, cromossomos B, drive, reprodução