The genomes of eukaryotes contain more genes than those of prokaryotes. Some of these “additional” genes encode functions associated with the compartmentalization of eukaryotic cells; others are needed to support multicellularity. The genome sequences of model organisms have been compared to identify common features of the eukaryotic genomes, including the presence of abundant regulatory sequences, repetitive sequences, and noncoding DNA. Some eukaryotic genes comprise gene families, which may include members that are mutated and nonfunctional.
learning outcomes
You should be able to:
Distinguish between the features of genomes or model organisms.
Predict why different plant species will differ in the features of their genomes.
Provide an evolutionary explanation for how gene families promote further evolution in vertebrates.
Summarize why the rRNA and tRNA genes involved in protein synthesis are present in multiple copies.
Describe the roles of a class of proteins found in Caenorhabditis elegans that has few counterparts in yeasts.
Genes for tissue formation are present in C. elegans but not in yeast.
What is the importance of gene families for evolution?
Gene families allow for evolutionary “tinkering.” If there are several copies of a gene in the genome, mutations in one copy of the gene may temper a harmful effect of the wild-
Why are there multiple copies of sequences coding for rRNA in the mammalian genome?
In some tissues, such as the egg cell, there is a need for massive protein synthesis (after fertilization) and therefore a need for a lot of ribosomes. The rate of transcription of the rRNA genes is not sufficient to meet the cell’s need for ribosomes, so there are multiple copies of the gene.
The genomes of rice, wheat, and corn are similar to one another and to that of Arabidopsis. What processes might explain why these four plants are nevertheless distinguished by unique proteins?
The four plants exist in different environments. For example, corn grows in drier and cooler regions than rice. Mutations of the basic plant genome allowed plants that carried them to adapt to the different environment to survive and reproduce.
The analysis of eukaryotic genomes has resulted in an enormous amount of useful information, as we have seen. In the next section we will look more closely at the human genome.