Non-human primate chromosomes mapped for the first time

Chromosome sequences from non-human primates have been completely mapped for the first time, marking a significant advancement in genetic research.

Scientists funded by the National Institutes of Health achieved this milestone, uncovering new insights into primate genetics.

Published in a recent edition of Nature, this study reveals a surprising degree of variation between the Y chromosomes of various primate species, underscoring a rapid evolutionary process.

This research not only fills in gaps in our understanding of great ape genomes but also enhances our insights into human evolution.

Chromosome sequences of non-human primates

The focus of the study was the X and Y chromosomes, which are crucial for sexual development and fertility.

The team successfully sequenced these chromosomes from five great ape species — chimpanzees, bonobos, gorillas, and both Bornean and Sumatran orangutans — as well as from the siamang gibbon, a primate more distantly related to humans.

Brandon Pickett, Ph.D., a postdoctoral fellow at the National Human Genome Research Institute (NHGRI), part of NIH, and a contributor to the study, emphasized the significance of this research.

“These chromosome sequences add a significant amount of new information. Previously, only the chimpanzee genome sequence was nearly complete, yet it contained large gaps, especially in regions of repetitive DNA.”

Decoding the DNA puzzle

This new data estimates that 62 to 66% of the X chromosomes and 75 to 82% of the Y chromosomes consist of repetitive DNA sequences.

Such sequences pose substantial challenges for genetic characterization, a task made feasible only recently through advanced DNA sequencing technologies and analysis methods.

By comparing the ape chromosomes with human ones, researchers could trace their evolutionary histories.

Interestingly, while the great ape Y chromosomes have far fewer genes than the X chromosomes, their structure showed high variability.

For instance, over 90% of the ape X chromosome sequences aligned with the human X chromosome, indicating little change over millions of years.

However, only 14% to 27% of the ape Y chromosome sequences showed alignment with the human Y chromosome.

Chromosome evolution in non-human primates

“The extent of the differences between the Y chromosomes of these species was very surprising,” noted Kateryna Makova, Ph.D., a professor and the study’s leader.

She explained that some primate species diverged from the human lineage as recently as seven million years ago. “This shows that the Y chromosomes are evolving very fast.”

One interesting aspect discovered was the variation in chromosome length among species, influenced by the number and types of DNA repeats. For example, the Y chromosome of the Sumatran orangutan is twice as long as that of the gibbon.

Another unique feature highlighted was the presence of palindromic DNA sequences — stretches of DNA that read the same forwards and backwards, much like the word “racecar.”

These palindromes, often spanning over a hundred thousand letters, contain genes that repeat many times, providing a backup to protect genes, particularly on the Y chromosome.

“Having these genes in palindromes is like keeping a backup copy. We expected to see the same genes in palindromes across different species, but this doesn’t seem to be the case,” added Adam Phillippy, Ph.D., a senior investigator at NHGRI and the study’s senior author.

Genetic diversity

Researchers also studied various genes within these palindromes on the chromosome sequences, many of which are crucial for sperm production and hence, fertility.

While palindromes appeared on all studied primate Y chromosome sequences, the specific palindrome sequences and the genes they contained often varied between species.

“There may be even more variation we’re not yet seeing. On the human Y chromosome, some genes can vary in number between individuals. For each of these other primate species, we’re only looking at a single individual. We don’t know what the rest of the population looks like yet and what other variations we might find,” Dr. Phillippy mentioned.

Conservation and evolutionary insights

These findings related to the chromosome sequences of non-human primates have practical implications for conservation efforts, especially since all studied great ape species are endangered.

“Not only can we learn about human evolution from these sequences, but we can also apply what we know about their genomes and human genomes to better understand the biology and reproduction of these endangered species,” Dr. Makova concluded.

This study, therefore, opens new avenues for exploring great ape genomes, offering a clearer picture of our closest living relatives and their evolutionary journeys.

The full study was published in the journal Nature.

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