问题 单项选择题

耳廓多毛症总是由父亲传给儿子,又由儿子传给孙子,决定这个性状的基因最可能在()

A.常染色体上

B.Y染色体上

C.X染色体上

D.X、Y染色体上

答案

参考答案:B

解析:

人的体细胞中有23对同源染色体,其中有一对与人的性别有关,叫做性染色体;男性的性染色体组成是X和Y,女性的性染色体组成是X和X。男性的Y染色体只能在男性之间逐代传递,而不会由男性传给女性;如果一个性状总是从父亲直接传给儿子,再由儿子直接传给孙子,那么控制这个性状的基因最可能位于Y染色体上,因此,A、C、D三项均错误,B项正确。

考点:本题考查性别决定和伴性遗传的相关知识,意在考查学生能理解所学知识的要点,把握知识间的内在联系,能运用所学知识对某些生物学问题进行解释、推理,做出合理的判断或得出正确结论的能力。

填空题


A How to Use a Painting Knife 使用画刀的方法
Painting with a knife is a bit like putting butter on bread and produces quite a (1) result to a brush. Painting knives are excellent for producing textured, impasto work and (2) areas of flat colour.
What’s the difference between a palette knife and a painting knife
A palette knife is a long, straight spatula that is used (3) mixing paints and scraping a palette clean. They’re made from metal, plastic, or wood and (4) either be completely straight or have a slightly bent handle. A painting knife has (5) large crank in the handle, which takes your hand away from the painting surface. They (6) in numerous shapes(for example pear-, diamond-, or trowel-shaped) and are used for painting (7) of a brush. The edge of the knife is blunt, so that it doesn’t cut the (8) .
·What shape of painting knife should I use
Different shaped painting knives produce different effects. For example, a short blade produces angular strokes (9)a long blade makes it easy to put down sweeps of colour.
·Why can’t I use a palette knife to paint with
You can. Painting (10) just have the advantage of coming in more angular shapes and with sharper points. And (11) larger crank in the handle means there’s less chance of rubbing your knuckles into wet (12) . If you’re unsure whether you’re going to enjoy painting with a knife, first buy a (13) , plastic palette knife and experiment a bit with this before upgrading to a wood-and-metal knife.
·How do I use painting knife
(14) the handle firmly so you’re got good control. Pick up some paint off your palette (15) the tip, as you’d pick up some butter with a knife. Use the side of the (16) to spread paint across your canvas, or press it onto the canvas, as you (17) spread butter across a slice of bread.It’ll seem strange at first as it’s quite (18) to using a brush. Using just the tip of the blade will produce small dots. (19) the edge of the knife down will produce fine lines. Pressing the blade flat down (20) the paint will produce ridges. Scrape back into the paint to reveal underlying layers (called sgraffito).

单项选择题