Homo habilis – First tool maker

TLS Online TPP Program

#Id: 3705

#Unit 2. Cellular Organization

Many genes are arranged along the chromosomes in groups of related genes. These groups are called gene clusters. Examples of gene clusters are the globin gene family.

TLS Online TPP Program

#Id: 3706

#Unit 2. Cellular Organization

When a genome contains a cluster of genes with related sequences, mispairing between nonallelic loci can cause unequal crossing over. This produces a deletion in one recombinant chromosome and a corresponding duplication in the other.

TLS Online TPP Program

#Id: 3707

#Unit 2. Cellular Organization

Thalassemias result from occurrence of unequal crossing that reduce or prevent synthesis of either a- or b-globin

TLS Online TPP Program

#Id: 3708

#Unit 2. Cellular Organization

Different thalassemias are caused by various deletions that eliminate a- or b-globin genes. The severity of the disease depends on the individual deletion.

TLS Online TPP Program

#Id: 3709

#Unit 2. Cellular Organization

Depending on the diploid combination of thalassemic alleles, an affected individual may have any number of a chains from zero to three.

TLS Online TPP Program

#Id: 3710

#Unit 2. Cellular Organization

if an individual has only one a gene, the excess b chains form the unusual tetramer b4, which causes hemoglobin H (HbH) disease. The complete absence of a genes results in hydrops fetalis, which is fatal at or before birth.