In the case of human chromosomes, approximately 300 G bands can usually be distinguished during metaphase. A larger number of G bands (in the range of 800) can be observed in prometaphase chromosomes because they are more extended than metaphase chromosomes.

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#Unit 11. Evolution and Behavior

Deletion plays a key role in gene trafficking.which is the movement of genes to new sites in the genome.

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#Id: 2246

#Unit 11. Evolution and Behavior

Some people have an allele called Δ32 at the CCR5 locus in which 32 bp are deleted.

CCR5 that plays a role in inflammatory response. Unfortunately, this protein is also a key to human immunodeficiency virus (HIV) infection. The virus binds to a loop of the CCR5 protein and then enters the cell.

The missing part of the gene codes for the loop in the protein to which the virus attaches. 

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#Id: 2247

#Unit 11. Evolution and Behavior

People who are Δ32 homozygous for the deletion are highly resistant to HIV, while heterozygotes are partly resistant.

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#Id: 2248

#Unit 11. Evolution and Behavior

These pieces— the exons —are separated by stretches of noncoding DNA— the introns

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#Id: 2249

#Unit 11. Evolution and Behavior

Chromosome Evolution

Fissions and fusion is the most common way for the number of chromosomes to change.

Humans have 23 pairs of chromosomes, but all of the other great apes have 24 pairs. At some point since our lineage split from that of chimpanzees, two chromosomes fused

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#Id: 2250

#Unit 11. Evolution and Behavior

A phenotypic distribution is determined by genetic and environmental factors.