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  • pg 1
									The patterns of
               inheritance                                    By Professor Valerie Corfield

Where did
you get
                            G    enes come in pairs
                                 because they are carried
                            in paired chromosomes. Only
                                                              grandpa’s or your grandma’s
                                                                 • The same is true for the

those eyes,                 one gene of each pair goes
                            into the sperm or egg that
                                                              genes you inherited from
                                                              your dad. You have either the
that nose?                  fuse together (at conception)
                            to make a baby.
                                                              version that came from his
                                                              mom or his dad (your other
                               New technology showns          grandma or grandpa).
                            us that very small differences       • If you have brothers or
                            in the DNA code in our genes      sisters, chance will deter-
                            result in different versions of   mine whether they got the
                            genes. These genetic differ-      same version of each gene as
                            ences make us look different      you, or whether they got the
                            from each other, for example      other version. That is why
                            whether we have blue or           you look different from each
                            brown eyes. How does this         other.
Designer babies                • One of every pair of         What happens if you
                            genes that your mom has           inherit two different
New DNA technology
                            came from her dad (your           versions of a gene?
that allows scientists to
                            grandpa)                             What happens if you
read genes raises the
                               • The other pair of genes      inherit two slightly different
question of whether
                            came from her mom (your           instructions, for example,
they can use the            grandma).                         the one to make blue eyes
information to produce         • When these genes were        and the one to make brown
designer babies. Will       separated into the egg that       eyes? Inheritance follows
parents be able to          made you, you inherited           its own laws and often one
order a baby boy with       either the version of your        gene version ‘wins’ over the

       an IQ of 200, with the                      other one. The feature (trait)     Following the                                                         in genetic counselling                             Grandparents
       ability to be a gold                        controlled by that particular      patterns and laws of                                                  in families who suffer
       medal winner in the                         gene is called dominant. The       inheritance                                                           from inherited dis-
       sport of choice, with                       one that ‘loses’ out is called        The laws that govern                                               eases.
       blue eyes or brown                          recessive.                         inheritance were first studied
       eyes and with model                            Brown eye colour is domi-       by an Austrian monk called                                     re         An experiment in
                                                                                                                                                 xtu                                                             Features
                                                                                                                                     r       r te                 genetics
       good looks?                                 nant over blue eye colour,         Gregor Mendel in the 1800’s.             olo
                                                                                                                                   u     hai
                                                   so if you have one gene ver-                                            ye c olour; ; chin
       As scientists begin to                                                         He worked with peas but his       • E air c mple                                   You can do an
       understand all the                          sion instructing your body to      discoveries apply to humans        • H hin di            s        st ril        experiment to
                                                   make blue eyes and the other                                           • C ape imple ze, no                           check the laws of
       information written                                                            and animals too. They have              sh er d e, si
                                                   telling it to make brown           helped people who study                  Oth e shap
                                                                                                                             • os                       h ape              inheritance in
       in our DNA, they                                                                                                                            ps
                                                   eyes, the brown-eye gene           genetics to understand how               • N ape and li                     e,         your own fami-
       will certainly be able                                                                                                     sh th                        tur
                                                                                                                                        u                  tex
                                                   will ‘win’. Recessive traits are   individual traits are inherited            • ndMo size hape,                            ly. Many facial
       to tell which genes                                                                                                             a brow s
                                                   only seen if you inherit two       and the patterns seen are                                                       r.
       specify desirable or                                                                                                              ye                       hai
                                                   copies of the gene that codes      called Mendelian inheritance.                   • E lour ape             ht                follow sim-                    Features
                                                                                                                                         co e sh         raig
       undesirable traits.                         for it, for example, if you get    Mendel’s laws are applied in                          ac or st                        ple Mendelian             Dad                     Mom
                                                                                                                                        • F rly
       (Continued on page 16)                      the blue-eye gene from both        plant and animal breeding                           •C                       patterns of inherit-
                                                   your mom and your dad.             programmes and are used                                               ance, and you will be

                                                                                                                                                                                                & sisters       Features

                                                                                                                                                                                                       able to see if they show a
Public Understanding of Biotechnology programme.

                                                                                                                                                                                                       dominant or a recessive pat-
From a poster by Rapid Phase (Pty) Ltd for the

                                                                                                                                                                                                       tern of inheritance. However,
                                                                                                                                                                                                       some inherited features are
                                                                                                                                                                                                       more complicated, so do not
                                                                                                                                                                                                       be surprised if some of the
                                                                                                                                                                                                       features you choose do not
                                                                                                                                                                                                       fit a straight forward pattern
                                                                                                                                                                                                       of inheritance.
                                                                                                                                                                                                           1) Make a list of what
                                                                                                                                                                                                       features you want to study
                                                                                                                                                                                                       in your family. Look at some
                                                                                                                                                                                                       ideas on the note.
                    14                                                                                                                                                                                                              15
Recently, for exam-         Any other feature char-
                                                           Extract DNA                                                         By Professor Valerie Corfield

                                                             from wheatgerm
ple, they identified a   acteristic of your family
version of a gene
that encourages peo-
                         (remember the story of the                                                                                                            DNA fact file
                         Hapsburg lip in the previous
ple to overeat and       issue?). What about other                                                                                                             • DNA stands for
                                                                                                                                                               deoxyribonucleic acid.
become fat.              body parts, e.g. hand and
They also know of
two genes that give
                         foot shapes? You can look at
                         photographs or ask your par-      T    his experiment will allow
                                                                you to extract one of the
                                                           building blocks of life – iso-
                                                                                              in 300 ml of tap water. Add
                                                                                              four squirts of lemon juice.
                                                                                              Now add half a cup of wheat-
                                                                                                                              stir the mixture until the
                                                                                                                              salt is dissolved and add six
                                                                                                                              teaspoons of alcohol. Add
                                                                                                                                                               • It is a chemical
                                                                                                                                                               substance made from
                                                                                                                                                               building blocks that
a person greater         ents about their grandparents                                                                                                         form long, thin strings.
                         and even their great grand-       lated DNA – from plant cells.      germ to the solution and        nine large drops of the wash-
athletic ability and                                       Although each DNA molecule         stir gently for 15 minutes.     ing-up liquid and stir gently.   • The DNA strings,
they can tell if that    parents. Don’t forget your                                                                                                            called molecules, are
                         aunts and uncles and your         is too small to see, if you fol-   The lemon juice will break      Add the soggy pulp from
person is likely to be                                                                                                                                         packed very tightly into
                         cousins.                          low the instructions, you will     down the cell walls of the      step one and stir it gently
                                                                                                                                                               the nucleus of cells.
a good sprinter or a                                       end up with visible DNA.           wheatgerm. Press this mix-      for about 20 minutes. During
                            2) Draw a pedigree show-                                                                                                           • The DNA molecules
long distance runner.                                                                         ture through the sieve and      this period, the detergent in    twist around each
                         ing all the relatives that you
However, changing        can investigate. Here is an                                          discard the liquid. You will    the washing-up liquid will       other and form a spi-
the DNA code to          example of how geneticists                                           be left with a soggy pulp. Do   dissolve the DNA into the        ral ladder – the DNA
put new forms of         draw a pedigree. You can                                             the same for the other half a   mixture. Now add about 10        double helix.
                                                               • A cup of wheatgerm
designer genes into      change this to fit your family.                                      cup of wheatgerm. The pulp      level teaspoons of salt and      • DNA double helixes
                                                                 (from health shops or
                                                                                              you now have contains the       stir gently for 10 minutes.      are organised into 23
a baby who hasn’t           3) Write the version of              some grocery stores)
                                                               • Table salt (about 8          cell contents without the                        Separate the    pairs of chromosomes
inherited them from      each chosen trait (such as              heaped teaspoons full)       cell walls.                                      DNA solution    in every cell in your
one of the parents is    curly or straight hair) under         • Clear alcohol (cane spir-                                                                     body.
not yet possible.        each relative on the pedigree.          it, gin or rubbing alcohol
                                                                                                                                                               • This set of chromo-
                         If you have studied a lot of            from the chemist)            Dissolve the DNA
In the end these                                               • Green dishwashing liq-                                                                        somes is the instruction
                         different traits, you might                                             Put one level tablespoon                                      manual to make YOU.
are issues of right                                              uid (not the gel type)
                         want to use abbreviations so          • Lemon juice (fresh or        of salt in 300                                                   • Each different
and wrong that
                         that you can list them under            bottled)                     ml of                                                            instruction is called a
will guide scientists                                          • Two glass bottles or         water,
                         each person on your pedi-                                                                                                             gene.
as to how far they                                               large glasses
                         gree.                                 • A sieve or strainer                                                                           • The gene instruc-
should interfere with                                          • Clean water                                                                                   tions are written in
                            4) What features ‘run’ in
nature to produce        your family? Can you see                                                                                                              a DNA code – the
designer babies.                                                                                                                                               genetic code.
                         examples of dominant traits
It is up to you, the                                                                                                                                           • New coded copies
                         (e.g. dark eye colour, dark          Break down the cell walls
                                                                                                                                                               are made when the
younger generation,      hair colour)? Can you see         of the wheatgerm
                                                                                                                                                               DNA double helix
to understand and        examples of recessive traits         In a large glass, dissolve                                                                       unzips down the
debate such issues.      (e.g. red hair, chin dimple)?     one level tablespoon of salt                                                                        middle.
                          from the mixture.                 Extract the dissolved
                             This step is easy. Just let    DNA from the solution
                          the mixture stand and allow          Take the quarter-filled
                          the solids to settle out.         glass, fill it up with alcohol
                          Then gently pour the liquid       and stir very gently. As you
                          into another glass, until it      stir, you will notice that the
                          is about a quarter full. Take     DNA precipitates out as very
                          care that the solids do not       fine white threads. You can
                          mix with the solution. The        leave this mixture to further
                          solution in the new glass         allow the DNA to settle.
                          now contains the DNA in a         Gently pour the liquid off and
                          dissolved form.                   there … you have DNA!

                          When DNA is
                          By Professor Valerie Corfield, US/MRC Centre for Molecular
                          and Cellular Biology, Faculty of Health Sciences, University
                          of Stellenbosch
                          J  ust like fingerprints, every
                             human has unique DNA.
                          Scientists have found ways to
                                                            body. DNA can be extracted
                                                            from hairs, skin cells, blood,
                                                            skeletons, bits of bone, teeth
Forensic science is the   tell one person’s DNA from        and body fluids left after a
study of objects that     another person’s; but unlike      crime. So when traditional
relate to a crime. This   fingerprints, which can be        fingerprints are fuzzy and not
evidence is analysed      changed using surgery, you        much help, DNA fingerprints
by the forensic scien-    can’t change your DNA. Also,      can speak out loud and clear.
tists, who observe,       unlike fingerprints, which are       DNA can last for a long
                          only left at a crime scene if     time, especially when it
classify, compare,
                          a person touches a suitable       is protected inside bones
count, measure,
                          surface with bare fingers,        and teeth. Scientists have
predict, and interpret
                          DNA is tucked away in the         developed ways to extract
data.                     centre of every cell in your      DNA and to do DNA fin-
Things have come a long way since
the days of Sherlock Holmes, when
the only tools a detective had were a
sharp eye, a magnifying glass and a
logical mind. Now police and scientists
have many new tricks to help solve
mysteries and crimes (forensic
science). These include:
•   autopsy (examining the dead body for evidence)
•   “traditional” fingerprinting
•   matching blood types (Are you O, A, B or AB?)
•   dental records
•   ballistics (study of guns)
•   chemical and fibre analysis (clothing etc)
•   x-rays
•   computer modelling
•   forensic entomology (study of insects)
•   DNA fingerprinting.

gerprinting tests from very        to be set free
small amounts of material,         when DNA tests
like a dried blood spot or         showed that they
even from cells in saliva left     did not commit the crime.
over from a person licking a       DNA fingerprinting was also
stamp.                             indispensable in identifying
   DNA fingerprinting has          victims of the September 11,
provided evidence used to          2001 bombing of the World
convict thousands of crimi-        Trade Centre in the United
nals. It also enables scientists   States, when scientists only
to look at old cases using         had scraps of tissue or shards
stored samples and evidence.       of bone or teeth to work
This has allowed many pris-        with.
oners who were found ‘guilty’         DNA fingerprinting has
                          also been used to solve long-    how are these DNA finger-
   FACT FILE              standing mysteries and iden-     prints made?
                          tify people who pretended to        When police have a sus-
                          be someone else (imposter).      pect, they take a blood
                          It can also be used to iden-     sample from that person and
Forensic scientists       tify how people are related      take the DNA from the blood
work in the labora-       (parentage), such as in the      cells. The forensic scientists
tory, in the field and    case of Happy Sindane. In        then focus in on specific
in the courtroom. To      addition, mummies and skel-      areas of the DNA that show
become a forensic         etons that are hundreds and      small differences between
scientist you will need   thousands of years old can       two people. The differences
a bachelor’s degree in    now “tell us” if they are male   between these different
science (chemistry and    or female, healthy or sick,      parts of the DNA generate a
biology); good speak-     related, even what they had      pattern, like a supermarket
                          for dinner, helping scientists   barcode, that is unique to
ing skills; good note-
                          to reconstruct the details of    the person the scientists are
taking and writing
                          how these people lived. If       investigating. This ‘barcode’
skills; curiosity and
                          only they’d tell us where they   is called a DNA fingerprint.
personal integrity.       hid the treasure...              Sometimes at crimes scenes,
                                                           only a very small amount of
                          But what exactly is a            DNA, such as one hair, is left
                          DNA fingerprint?                 behind. In cases like these,
 From a poster by           A DNA fingerprint looks        the target areas of the DNA
 Rapid Phase (Pty)
 Ltd for the Public       very different from an inky      can be ‘copied’ so scientists
 Understanding of         thumbprint on a page. So
                                                           then have enough to make a
 programme.               what does it look like and       DNA fingerprint.


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