Name:____________________
Grade 10 Science Related Reading/Biology
Class:____________________
Biology Gr10
Date:____________________
DNA and Protein Synthesis
Double take
By studying twins, scientists help us understand what makes people who they are. There
are two types of twins; identical and fraternal twins.
Identical twins begin life in the womb as a single fertilized egg. The egg begins to grow
normally into a single embryo. Then, for unknown reasons, the embryo splits in two. This
usually happens during the first two weeks of growth. About nine months later, two
babies are born that often look so similar even their parents can have trouble telling them
apart.
Reading Check
What are the two types of
twins ?
_____________
_____________
Identical twins form when a fertilized embryo splits into two embryos
early in development. These twins get the same genes from their parents,
but such siblings aren’t the same people.
The second type of twins is called fraternal. These twins develop when two eggs are
fertilized. Fraternal twins are much like regular siblings. They just happen to grow
together inside their mother. These twins can be boys, girls, or one of each. Identical
twins, on the other hand, always belong to the same gender.
What makes twins interesting to scientists is their DNA. This molecule acts like the
instruction manual for life. Stretches of DNA are called genes. And genes determine the
color of your eyes, how tall you are, which diseases you might be likely to develop and
more.
DNA directs the cell’s activities by telling it what proteins to make and when. These
proteins form structural elements in the cell and regulate the production of other cell
products. By controlling protein synthesis, DNA is hugely important in directing life.
1
Grade 10 Science Related Reading/Biology
Protein synthesis is a two-step process. DNA resides in the nucleus, but proteins are made
in the cytoplasm. The cell copies the information held in DNA onto RNA molecules in a
process called transcription. Proteins are synthesized at the ribosomes from the codes in
RNA in a process called translation.
Looking closer
Where exactly in the cell does
transcription take place?
_________________________
_________________________
__
Vocabulary Development
What key vocabulary terms are contained in this
passage?
___________________________
___________________________
___________________________
People have billions of cells in their bodies. In every cell, DNA is grouped into 23 pairs
of threadlike structures called chromosomes. One chromosome in each pair comes from
your mother. The other chromosome in each pair comes from your father.
During reproduction, genes from both parents get scrambled into a new combination of
chromosomes in the child. In ordinary siblings and fraternal twins, each person gets a
different mixture of genes from mom and dad. That explains why you might have your
mother’s mouth and your father’s eyes, while your brother has the opposite combination.
In identical twins, on the other hand, each person gets exactly the same genes from each
parent. Genetically, these siblings are like clones of each other.
Ever since the discovery of DNA in the 1950s, scientists have wondered how important
genes really are. Do these microscopic snippets determine whether we like sports, are
good at art and everything else about us? Or are our personalities a result of the way
we’re raised and the experiences we have?
2
Grade 10 Science Related Reading/Biology
Researchers now know that the answer lies somewhere in the middle. Genes determine
our potential. But the environment often determines whether genes are turned on or off.
Identical twins illustrate that concept perfectly. If genes, or nature, alone determined
everything about us, you’d expect identical twins to be identical in every way. Despite
their similar looks, however, twins often prefer different types of music, friends, clothes
and more.
Tracking twins
Researchers at the University of Minnesota found that, in many ways, identical twins are
far more alike than fraternal twins, even when those identical twins are raised apart.
These similarities are true for a large number of personality traits, such as how outgoing
people are, how aggressive they are and what types of decisions they tend to make. These
results suggest that genes play important roles in determining our personalities.
At the same time, researchers want to know why sometimes only one twin develops a
serious disease. What is it about the environment that pushes certain genes to turn on or
off?
One possibility is that what happens in the womb influences how genes end up behaving
many years later. This is something scientists are currently investigating. One day, the
work might lead to simple but life-changing advice, like what moms should eat when
pregnant.
These days, scientists are using twin studies to investigate everything from the
complexities of genetics to the reasons why people vote the way they do.
Questions
Choose the right answer:
1. Identical twins develop from ---------------------------------a. One fertilized egg
c. two fertilized eggs
b. One unfertilized egg
d. two unfertilized eggs
2. What makes twins interesting is their ------------------------a. Gender
c. DNA
b. Behavior
d. diseases
3
Grade 10 Science Related Reading/Biology
3. The process of translation takes place in the ----------------------a. Nucleus
c. mitochondria
b. Ribosomes
d. lysosomes
4. The number of human chromosomes is ----------------------------a. 23
c. 23 pairs
b. 47
d. 22 pairs
5. What makes twins so similar?
a. Having similar genes
b. Growing up in the same household at the same time.
c. sharing all household experiences at the same age
d. having the same quality of education
Compare between the following terms: chromosome - DNA – Gene
Chromosome
DNA
Gene
Answer the Following Questions:
1. What distinguishes twins from other pairs of brothers and sisters?
__________________________________________________________________
_________________________________________________________________
2. What do you think scientists hope to learn by studying twins?
__________________________________________________________________
__________________________________________________________________
3. What’s the difference between fraternal and identical twins? And what
happens differently in the womb to give rise to one type of twins or the other?
4
Grade 10 Science Related Reading/Biology
________________________________________________________________________
________________________________________________________________________
_______________________________________________________________________
4. Why do people have chromosomes in their cells in the form of pairs ?
______________________________________________________________________
_______________________________________________________________________
5. What kinds of information can the study of twins offer that might apply to
non-twins?
________________________________________________________________________
_______________________________________________________________________
6. When women go to fertility clinics and end up having multiple babies — what
kinds of twins or triplets or quadruplets do these tend to be: fraternal or
identical?
________________________________________________________________________
_______________________________________________________________________
7. Even identical twins can have different traits — from height and health to
personality. What factors can lead to such differences?
_______________________________________________________________________
________________________________________________________________________
8. Briefly compare the processes of transcription and translation.
________________________________________________________________________
_______________________________________________________________________
9. Explain why was the DNA described in the passage as being the instruction
manual for life ?
______________________________________________________________________
________________________________________________________________________
5