meiosis: Hybrid G. hirsutum x G. thurberi Pairing arrangement 13 small bivalents + 13 large univalents G. hirsutum x G. herbaceum 13 large bivalents + 13 small univalents G. thurberi 13 large univalents x G. herbaceum + 13 small univalents
Evolution
The history and science of origin and evolution comprise two events, the beginning of life and expansion of life. Our earth originated about 4.5 billion years ago. The term evolution is derived from two Latin words and means the act of unfolding or unrolling. English philosopher Herbert Spencer first used it. Evolution is defined as the change in heritable traits of biological populations over successive generations. These traits are the manifestations of genes that are passed down from parent to offspring during reproduction.
Cladistics
Cladistics is a technique in the classification of organisms, where they are grouped into different clades. The proof for the relationships that are hypothesized is based on the shared derived characteristics known as synapomorphies. These characteristics do not exist in many of the distant ancestors and groups. The common ancestor along with its descendants is considered to be a part of the clade. The rate of closeness is directly proportional to the cladistic grouping and is useful in analyzing the evolutionary mechanism.
Outgroups
Outgroups are significant in studying cladistics or phylogenetics (that describe the evolutionary relationship between different organisms). Further, it is also important to understand the differences and similarities between different organisms.
Taxonomy
It is the branch of biology that works with the identification of organisms at first, then naming, and classification of them into phenetic or phylogenetic groups (a classification system). In other words, it is the scientific study of biological diversity and a part of systematic biology.
Phylogenetics
Phylogenetics is the scientific study of how various groups of organisms are related at the evolutionary level. It finds the relationship between various organisms based on their evolutionary similarities and differences. It is a part of the taxonomy. Although the taxonomic study is not only concerned about phylogeny but taxonomic studies are also concerned about the classification and nomenclature of the different individuals from different taxon.
The New World cotton species Gossypium hirsutum has a
2n chromosome number of 52. The Old World species
G. thurberi and G. herbaceum each have a 2n number of
26. When these species are crossed, the resulting hybrids
show the following chromosome pairing arrangements at
meiosis: Interpret these observations phylogenetically, using
diagrams. Clearly indicate the relationships between the
species. How would you prove that your interpretation is
correct?(PICTURE ADDED)
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