Navigation Links
Researchers peek at the early evolution of sex chromosomes

CHAMPAIGN, Ill. Two new studies offer insight into sex chromosome evolution by focusing on papaya, a multimillion dollar crop plant with a sexual problem (as far as growers are concerned) and a complicated past. The findings are described in two papers in the Proceedings of the National Academy of Sciences.

The research reveals that the papaya sex chromosomes have undergone dramatic changes in their short evolutionary histories (they are about 7 million years old; by comparison, human sex chromosomes began their evolution more than 167 million years ago). One of the two studies compares the papaya X chromosome with that of a closely related non-sex chromosome (called an autosome) in a sister species. The other looks at differences between the X and Y chromosomes.

The studies show that the papaya sex chromosomes are increasing in size mostly through the accumulation of repetitive sequences while also reorganizing themselves and losing some genes carried over from their days as autosomes. Some of the lost genes are gone without a trace, while other remnants of genes that are no longer functional called "pseudogenes" are still present. The papaya Y chromosome also has independently gained some genes from the autosomes, the researchers report.

Gene loss in the Y chromosome is well documented in ancient Y chromosomes, but gene loss in the X chromosome, particularly at this early stage, is unexpected, as is the expansion of the X chromosome, said University of Illinois plant biology professor Ray Ming, who led both studies.

"The pace of gaining repetitive sequences and losing genes is faster in the Y than in the X chromosome, however," he said.

"This is the first look at an early stage of sex chromosome evolution," said Andrea Gschwend, who conducted the research with Ming while she was a doctoral student in his lab. "Usually people will focus on the ancient sex chromosomes because they are the most relevant to us," she said. "So this is the first direct and complete look at a more recently evolved sex chromosome system."

Analyzing the X chromosome is vital to understanding the evolution of sex, said Ming, an affiliate of the Institute for Genomic Biology at Illinois. The new findings in papaya suggest that the human X chromosome, too, has undergone numerous changes since it first distinguished itself from the autosomes, Ming said. Such changes are not detectable because the ancestral autosomes are no longer available for comparison, he said.

Because the papaya sex chromosomes are young and can be compared to closely related autosomes in a sister species, they offer a view of the early events of both X and Y chromosome evolution, Ming said.

Studying papaya sex chromosomes is a complicated task, however. The papaya has male, female and hermaphrodite sexual types, with two kinds of Y chromosomes (the male Y and the slightly modified, hermaphrodite Yh). Papaya plants may produce combinations of male and female (from the XY system) or hermaphrodite and female (from the XYh system) plants.

This complexity causes problems for papaya growers, Ming said. Hermaphrodites are the most productive of the papaya sexual types and yield the best fruit, but the offspring of hermaphrodites are not all hermaphrodites. To aid growers, Ming and his colleagues aim to develop a "true-breeding" hermaphrodite papaya variety that consistently produces hermaphrodite offspring.

When the researchers compared the X chromosome and the hermaphrodite Yh chromosome, they discovered that two major sequence inversions in the sex-determining regions of the Yh had taken place. One of these inversions occurred about 7 million years ago, and led the sex chromosomes and the autosomes down very different evolutionary paths, Ming said. The second inversion occurred about 1.9 million years ago and led to further differentiation between them. Each inversion has also undergone numerous sequence rearrangements, he said.

All of the findings are significant and useful, Ming said, but the X chromosome, which is generally overlooked in models of sex chromosome evolution, offered the most surprises.

"These studies are changing our view of sex chromosome evolution, particularly X chromosome evolution," he said. "We now know that both the X and Y chromosomes are dynamic in the early stages of their evolution, not only the Y chromosome, as previously thought."

Contact: Diana Yates, Life Sciences Editor
University of Illinois at Urbana-Champaign

Related biology technology :

1. SRI International Researchers Developing Bioadhesive Gel to Protect Women from HIV and HSV Infections
2. Researchers create highly conductive and elastic conductors using silver nanowires
3. Researchers create rubber-band electronics
4. Cedars-Sinai researchers, with stem cells and global colleagues, develop Huntingtons research tool
5. Penn researchers study of phase change materials could lead to better computer memory
6. Researchers tune the strain in graphene drumheads to create quantum dots
7. WHEATON® Introduces a New Web Community for Scientists, Researchers, and Biopharmaceutical Packagers
8. Stevenage Bioscience Catalyst to Welcome Cambridge University Researchers
9. Syracuse University researchers use nanotechnology to harness power of fireflies
10. Researchers discover hereditary enzyme deficiency
11. JCVI Researchers, as Part of NIH Human Microbiome Project Consortium, Publish Papers Detailing the Variety and Abundance of Microbes Living on and in the Human Body
Post Your Comments:
Related Image:
Researchers peek at the early evolution of sex chromosomes
(Date:11/25/2015)... LOS ANGELES and HOLLISTON, Mass. ... Regenerative Technology, Inc. (Nasdaq: HART ), a biotechnology ... announced that CEO Jim McGorry will present ... Tuesday, December 1, 2015 at 2:30 p.m. PT. The ... (link below) for 30 days. Management will also be ...
(Date:11/25/2015)... ... November 25, 2015 , ... A long-standing ... Aerospace Professionals (OPBAP) has been formalized with the signing of a Memorandum of ... with OPBAP leaders Capt. Karl Minter and Capt. Albert Glenn Tuesday, November 24, ...
(Date:11/25/2015)... (PRWEB) , ... November 25, 2015 , ... ... company uBiome, were featured on AngelList early in their initial angel funding process. ... AngelList syndicate for individuals looking to make early stage investments in the microbiome ...
(Date:11/24/2015)... , Nov. 24, 2015 Cepheid (NASDAQ: ... speaking at the following conference, and invited investors to ... NY      Tuesday, December 1, 2015 at 11.00 ... NY      Tuesday, December 1, 2015 at 11.00 ... Conference, New York, NY      Tuesday, ...
Breaking Biology Technology:
(Date:11/2/2015)... , Nov. 2, 2015  SRI International has been ... provide preclinical development services to the National Cancer Institute ... will provide scientific expertise, modern testing and support facilities, ... preclinical pharmacology and toxicology studies to evaluate potential cancer ... The PREVENT Cancer Drug Development Program is an ...
(Date:10/29/2015)... -- Connected health pioneer, Joseph C. Kvedar , MD, ... and wellness, and the business opportunities that arise from ... of Healthy Things . Long before health and ... Kvedar, vice president, Connected Health, Partners HealthCare, was creating ... from the hospital or doctor,s office into the day-to-day ...
(Date:10/27/2015)... Calif. , Oct. 27, 2015 Synaptics Inc. ... solutions, today announced that Google has adopted the Synaptics ... touch controller solutions to power its newest flagship smartphones, ... by Huawei. --> ... like Google to provide strategic collaboration in the joint ...
Breaking Biology News(10 mins):