首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
In the 1960s scientists begin to recognize that environmental contaminants could not only affect the health and survival of indi
In the 1960s scientists begin to recognize that environmental contaminants could not only affect the health and survival of indi
admin
2014-01-09
49
问题
In the 1960s scientists begin to recognize that environmental contaminants could not only affect the health and survival of individual animals but also alter the prospects for their off-spring and thereby potentially change the genetic makeup of entire populations.
Researchers were first altered to problems in wildlife in the 40s after the populations of eagles, falcons, and the other fish-eating birds in Britain plummeted. In nest after nest the birds’ eggshells were so thin that they cracked under the weight of the adults during incubation. In the 1960s David Peakall and other wildlife toxicologists demonstrated that the accumulation of very high levels of such pesticides as DDT in the birds’ tissues had seriously impaired their productive capabilities. Some of these declines resulted in the complete disappearance of populations from large portions of their former range. In North America, for example, the eastern population of the peregrine falcon was virtually wiped out. More recently, the Golf Coast population of the brown pelican disappeared as a result of eggshell thinning thought to be caused by the organochlorine pesticides dieldrin and endrin.
Since then, researchers have provided additional evidence that environmental pollution can affect future generations. For example, exposure to high levels of PCBs has been shown to affect the learning and behavior of children. In the 1980s Snadra W. Jacobson and Joseph L. Jacobson of Wayne State University, Detroit, Michigan, studied a group of children whose mothers had eaten PCB—contained fish from Lake Michigan. The researchers found that the children’s prenatal exposure to these compounds resulted in neurological anomalies at birth and developmental delays in motor function during infancy. The Jacobson retested the children at age 11. In a 1996 report they noted that the children exhibited significantly poorer intellectual function, amounting to a 6.2 point deficit in the IQs of the most highly exposed subjects.
Contaminants also have been linked to a critical loss of genetic variability in populations of living organisms. One of the best studies of this phenomenon was published in 1994 by M. H Murdoch and P.D.N. Hebert of the University of Guelph, Ontario. The study measured the variations in the mitochondrial DNA (mtDNA) of populations of brown bullhead catfish in the Great Lakes, comparing bullheads from pristine reference areas with bullheads living in heavily contaminated with such pollutants as organochlorines and petrochemicals. The two researchers used one of the most powerful tools of modern molecular population genetics-molecular analysis of DNA. By revealing differences in the specific code, i.e., in the sequence of nucleotides, contained in the DNA of a particular gene, the technique can help identify and quantify genetic variety within and among populations. For their study, Murdoch and Hebert examinated variations in genes of the cellular mitochondria, which possess their own DNA (mtDNA) that is distinct from the DNA found in the cell nucleus. Because mitochondrial genes are not "shuffled" in the production of sperm and egg cells, as are nuclear genes, and because they are transmitted to offspring only by the mother, they are ideal for charting the relatedness and evolutionary history of spaces.
The researchers found that although the numbers of fish were abundant in both types of sites, the levels of genetic variability were always significantly higher in the pristine areas. The most likely explanation is that bullheads populations in polluted waters crashed after their initial contact with contaminants, but the remaining fish were able to repopulate because a few individuals possessed rare genes that allowed them to adapt and survive. Thus, even though the bullhead populations appeared to be thriving in contaminated areas, the genetic makeup of their populations had undergone a damaging simplification, a depletion of the storehouse of adaptations that animals can draw upon to surmount environmental challenges such as the introduction of a new disease of fluctuations in climate. Their genetic diversity potentially could be quickly increased by the influx of new genes from migrant fish, but most fish from other populations might survive in the polluted sites long enough to contribute to the gene pool.
From the passage, we know that dieldrin is ______.
选项
A、a kind of falcon
B、a kind of pesticides
C、a kind of catfish
D、not mentioned in the passage
答案
B
解析
是一种杀虫剂。A.猛禽与C.catfish均不正确。
转载请注明原文地址:https://jikaoti.com/ti/bR7YFFFM
0
专业英语八级
相关试题推荐
Whichofthefollowingreasonsdoscientistssupportthatcanexplaintheextinctionofdinosaurs?
Scientistshavelongbelievedthatconstructingmemoriesislikeplayingwithneurologicaltoys.Exposedtoabarrageofsensati
Scientistshavelongbelievedthatconstructingmemoriesislikeplayingwithneurologicaltoys.Exposedtoabarrageofsensati
Scientistshavelongbelievedthatconstructingmemoriesislikeplayingwithneurologicaltoys.Exposedtoabarrageofsensati
Fast-foodfirmshavetobeathick-skinnedbunch.Healthexpertsregularlylambastethemforpeddlingfoodthatmakespeoplefat
随机试题
原发性不孕症的定义是:
医师在执业活动中,有下列行为之一的,予以警告或责令暂停六个月以上一年以下执业活动,情节严重的,吊销其执业证书,构成犯罪的,追究其刑事责任,除了
5月19日,某教学楼工程施工现场在混凝土浇筑过程中,发生模板坍塌事故,造成6人死亡、18人受伤,直接经济损失357万元。该教学楼为框架结构,建筑面积11800m2,事故发生的部位是教学楼中部的共享大厅,该大厅是一个高度为16.5m,进深为15m,长边
(1)请说明企业人力资源管理费用包括哪些基本项目?(2)说明编制人力资源管理费用预算的基本程序和方法。
某市卫生防疫站经市卫生局批准以后,以该站名义对某饭店做出了处罚决定.该饭店不服处罚决定向人民法院提起行政诉讼。下列说法正确的是()。
许多孕妇都出现了维生素缺乏的症状,但这通常不是由于孕妇的饮食中缺乏维生素,而是由于腹内婴儿的生长使她们比其他人对维生素有更高的需求。为了评价上述结论的确切程度,以下哪项操作最为重要?()
It’spossiblethatwhileyouareatwork,youmaydreamaboutamonthofSundays,butyourbosswishesforaweekofTuesday.
在社会公共生活中,衣着整齐得体,不袒胸赤膊;礼让老幼病残,礼让女士;不讲粗话;不在公共场所大声喧哗等。这体现了社会公德中
Thisspecialcommitteewasestablishedforwell-integratedmembersofthesocietyandnotfor______individuals.
Intheearly1970’s,CitibankofNewYorkCitybecameoneofthefirstfinancialinstitutionstoinstallATM’sonalargescale.
最新回复
(
0
)