(Grade 7 Biology)
Study Guide: Variation, DNA & Genes
Part 1: What is Variation? (第一部分：什么是变异)
Variation means differences among living things of the same species.
变异是指同一种生物之间的不同之处。
Two main types:
两种主要类型：
Inherited Variation (遗传变异)
Environmental Variation (环境变异)
Passed from parents via DNA (通过 DNA 从父
Caused by lifestyle, climate, accidents, or diet (由生活
母遗传)
方式、气候、事故或饮食引起)
Example: natural hair color, blood type, chin
shape (例如：自然发色、血型、下巴形状)
Example: calluses on hands, pierced ears, tanned skin
(例如：手上的老茧、耳洞、晒黑的皮肤)
Cannot be changed by effort alone (无法单靠努
Can change during life (在一生中可以改变)
力改变)
✅ Remember:
✅ 记住：

You are born with inherited traits. (你天生就有遗传特征。)

You acquire environmental traits after birth. (你出生后获得环境特征。)
(Grade 7 Biology)
Part 2: DNA – The Molecule of Life (第二部分：DNA – 生命分子)
DNA carries all the instructions for building and running a living thing.
DNA 携带建造和运行生物体的所有指令。
Where is DNA found? (DNA 位于哪里)

In animals and plants, DNA is inside the nucleus (the control center of the cell).
在动物和植物中，DNA 位于细胞核内（细胞的控制中心）。

Bacteria also have DNA, but not inside a nucleus.
细菌也有 DNA，但不在细胞核内。
What shape is DNA? (DNA 是什么形状?)

Double helix – like a twisted ladder or spiral staircase.
双螺旋 – 像一个扭曲的梯子或螺旋楼梯。
What are genes? (什么是基因?)

A gene is one small section of DNA that gives a single instruction (e.g., “make brown
eyes”).
基因是 DNA 上的一个小片段，提供一条指令（例如：“制造棕色眼睛”）。

Genes work like a recipe book for your body.
基因就像你身体的食谱书。
(Grade 7 Biology)
Part 3: DNA Base Pairs (The "Alphabet" of DNA)
(第三部分：DNA 碱基对 – DNA 的“字母表”)
DNA has 4 chemical bases: A, T, C, G
DNA 有 4 种化学碱基：A、T、C、G
They always pair in a specific way:
它们总是按照特定方式配对：

A always pairs with T (A 总是与 T 配对)

C always pairs with G (C 总是与 G 配对)
Easy memory trick (简单记忆技巧):
Apple → Tree
Car → Garage
If one DNA strand has: A T C G
如果一条 DNA 链上有：A T C G
The matching strand will be: T A G C
那么配对的链就是：T A G C
(Grade 7 Biology)
Practice Questions (练习题 – 自己试一试！)
Question 1 – Variation (变异)
Which of these is inherited variation?
以下哪一个是遗传变异？
A. A scar from cooking accident (烹饪事故留下的伤疤)
B. Being able to roll your tongue (能够卷舌头 – 天生的能力)
C. Learning to ride a bicycle (学会骑自行车)
D. Growing bigger muscles from exercise (通过锻炼长出更大的肌肉)
Question 2 – DNA location (DNA 位置)
A scientist looks at a cheek cell under a microscope. Where should she look to find most of the
DNA? 科学家在显微镜下观察一个脸颊细胞。她应该在哪里找到大部分 DNA？
A. Floating in the cytoplasm (漂浮在细胞质中)
B. Inside the nucleus (细胞核内)
C. Attached to the cell membrane (附着在细胞膜上)
D. Inside a vacuole (液泡内)
Question 3 – Gene function (基因功能)
What is the main job of a gene inside a cell?
细胞内基因的主要工作是什么？
A. To store energy for later use (为以后储存能量)
B. To carry oxygen to all parts of the body (将氧气输送到身体各处)
C. To provide instructions for making a specific trait (为制造特定特征提供指令)
D. To digest food inside the cell (消化细胞内的食物)
(Grade 7 Biology)
Question 4 – True or false? (Correct the false ones) (判断对错 – 错误的
请改正)
a) If a mother dyes her hair blonde, her children will be born with blonde hair.
如果母亲把头发染成金色，她的孩子天生就会长金色头发。
__________________________________________________________________________
b) Identical twins have very similar DNA because they come from the same egg and sperm.
同卵双胞胎拥有非常相似的 DNA，因为他们来自同一个卵子和精子。
__________________________________________________________________________
c)
What you eat for breakfast can change the color of your eyes.
你早餐吃什么可以改变你眼睛的颜色。
__________________________________________________________________________
d)
A dog’s fur color is an example of inherited variation.
狗的毛色是遗传变异的一个例子。
__________________________________________________________________________
Question 5 – DNA shape (DNA 形状)
Describe the shape of a DNA molecule using only two words.
仅用两个词描述 DNA 分子的形状。
Answer: _______________________________________________________
(Grade 7 Biology)
Question 6 – Base pairing (碱基配对)
Complete the matching DNA strand for each sequence.
完成每条序列的配对 DNA 链。
Sequence 1 (序列 1):
ACTGGCGGCGCAT
__ __ __ __ __ __ __ __ __ __ __ __ __
Sequence 2 (序列 2):
TGCAGGCTACTGC
__ __ __ __ __ __ __ __ __ __ __ __ __
__ __ __ __ __ __ __ __ __ __ __ __ __
Question 7 – Thinking deeper (深入思考)
Mia has attached earlobes (a trait she was born with). Her friend Ben has pierced ears.
米娅有贴附耳垂（她天生的特征）。她的朋友本打了耳洞。

Which trait is inherited? (哪个特征是遗传的？)
______________________________________________

Which trait is environmental? (哪个特征是环境的？)
______________________________________________

If Mia has a baby, will the baby definitely have attached earlobes? Why or why not?
如果米娅生一个宝宝，宝宝一定会有贴附耳垂吗？为什么？
______________________________________________