Cyclical sectors such as mining and oil services were bearing the brunt of the market sell-off on Friday as fears about a global economic slowdown prompted investors to scale back risk appetite.Mining heavyweights such as Antofagasta, Glencore, Fresnillo and BHP Billiton were all under pressure as markets showed concerns with how subdued growth would affect the demand for natural resources.Meanwhile, a continued slump in the price of crude was affecting stocks in the oil services sector with Brent trading near a four-year low amid slowing demand and expanding output. Amec, Petrofac, Lamprell and Wood Group were all suffering heavy losses.Wood Group, which delivered a well-received trading update on Thursday, was among the worst-performers after Numis Securities downgraded the stock from 'add' to 'hold', saying it has become "much more levered to oil prices than we had appreciated, particularly in the US onshore market".The broker said that visibility of client spend in the US shale market is low, and with oil prices so depressed there is an increased risk of a reduction in US onshore rig count associated capital expenditure.In contrast, shares in defensive categories such as telecoms and real estate were bucking the trend with stocks such as BT Group, Kcom, Talktalk, Hammerson, British Land and Land Securities registering gains.Defensives are companies whose earnings and dividends tend to be relatively stable in times of market and economic volatility.Utility services group Telecom Plus meanwhile jumped 7% after delivering an impressive trading update. The company said it was "comfortable" with consensus forecasts after a strong pick-up in growth in the second quarter. Top performing sectors so far todayFixed Line Telecommunications 4,207.35 +0.33%Real Estate Investment Trusts 2,729.39 +0.23%Forestry & Paper 10,308.19 +0.10%Bottom performing sectors so far todayTechnology Hardware & Equipment 1,015.20 -3.11%Mining 15,082.57 -2.62%Industrial Engineering 8,951.34 -2.40%Oil Equipment, Services & Distribution 20,704.13 -2.32%Industrial Metals & Mining 1,272.71 -2.13%