Genetics
20 Things You Didn’t Know About... DNA - Discover Mag
By Kirsten Weir|Monday, June 13, 2011
• 1 Sorry, Jimmy: James Watsonand Francis Crick did not discover
DNA. That honor goes to Swiss biochemist Friedrich Miescher, who
in 1869 found the molecule in the nuclei of white blood cells and
called it nuclein.
• 2 Nor did they figure out that DNA is our genetic blueprint;
bacteriologist Oswald Avery and his colleagues did that in the early
1940s.
• 3 What Watson and Crick did do, in 1953, was decipher the doublehelix structure of DNA. Their discovery ran as a single-page paper in
Nature.
• 4 Phosphorus is a key component of DNA, but late last year a team
of NASA scientists published a controversial study reporting that
they had found abacterium that could use arsenic instead. “What
else can life do that we haven’t seen yet?” wondered lead
researcher Felisa Wolfe-Simon.
• 5 Don’t try this at home: If uncoiled, the DNA in all the cells in your
body would stretch 10 billion miles—from here to Pluto and back.
• 20 Things You Didn’t Know About... DNA - Discover
Mag
• 6 Most of that DNA resides not in the cell nuclei,
which control heredity, but in our mitochondria, the
organelles (units within cells) that generate metabolic
energy!
• 8 Aside from bacteria, the smallest genome belongs to
the intestinal parasiteEncephalitozoon intestinalis, with
a trifling 2.3 billion base pairs.
• 9 Scientists are working to create vaccines against HIV,
flu, and hepatitis C from snippets of synthetic DNA; the
DNA tricks the body into producing harmless viral
proteins that train the immune system to attack real
viruses.
• 10 DNA vaccines for West Nile virus, melanoma, and
hemorrhagic disease are already available for horses,
dogs, and salmon, respectively.
• 11 At the Chinese University of Hong Kong, fetal DNA was extracted
from a pregnant woman’s blood plasma and tested for Down
syndrome. Prenatal DNA screening could someday replace
amniocentesis.
• 12 Telomeres, sequences of DNA at the tips of chromosomes, get
shorter every time a cell divides; when they get too short, the cell
dies. Some scientists are trying to extend life by extending the
telomere.
• 13 Good news if you’re a mouse: Researchers at Dana Farber
Cancer Institute in Boston engineered mice with telomerase (an
enzyme that adds DNA to telomeres) that could be switched on and
off. With the enzyme activated, the mice grew new brain cells and
lived longer.
• 14 Bad news if you’re a mouse: Scientists at Osaka University
recently developed mice that are especially susceptible to DNA
copying errors, seeking to increase the rate of mutations and see
what new traits appear.
• 15 The results so far include short-legged mice, mice with fewer
toes than normal, and mice that chirp like songbirds.
• 16 Guess who’s in your DNA? At least 8 percent of the human
genome originated in viruses, whose genetic code was integrated
with ours over roughly 40 million years of primate evolution.
• 17 Over the next five years, the International Barcode of Life
Project aims to establish genetic identifiers for 500,000 species—
short sections of unique DNA in the same location on the genome,
a bit like the UPC on your box of Froot Loops.
• 18 Already, forensic specialists can identify criminals from traces of
“touch DNA” left in fingerprints at a crime scene.
• 19 Next up: food forensics. British microbiologists sequenced DNA
to identify the bacteria in a round of Stilton blue. They found that at
least six microbial groups influence the flavor of the cheese’s “dairy
matrix.”
• 20 And scientists at the University of Guelph in Ontario showed
that DNA from the worm (actually an agave butterfly caterpillar)
traditionally placed in bottles of mescal leaches into the liquor. So
now we know: You don’t actually have to “swallow the worm” to
swallow the worm.
Inherited information is located in the nucleus of
every cell in the organism. The information is
coded in the huge DNA molecule. The huge
molecules are coiled into compact hot dog-shaped
structures called chromosomes. Chromosomes are
always present in almost identical pairs. Locations
on chromosomes that affect features of organisms
are called genes. A gene is composed of 2 alleles.
An organisms unique combination of genes is its
genotype. The traits produced by an organisms’s
genes is its phenotype. Alleles that have more
influence in determining traits are dominant alleles.
Alleles that have less influence in determining traits
are recessive alleles.
Chromosomes (Inherited information) are
located in the nucleus of every cell in the
organism.
The information is coded in the huge DNA
molecule.
The huge molecules are coiled into compact hot
dog-shaped structures called chromosomes.
• Chromosomes are always present in almost
identical pairs.
• Locations on chromosomes that affect
features of organisms are called genes.
• A gene is composed of 2 alleles.
• An organisms unique combination of genes is
its genotype.
• The traits produced by an organisms’s genes is
its phenotype.
Alleles that have more influence in determining
traits are dominant alleles.
Alleles that have less influence in determining
traits are recessive alleles.
Lab pg 55 – four boxes
•
•
•
•
Chromosome
Gene
Nucleus (nucleoplasm)
allele
Chromosomes
• Q1- Located in the nucleus of a eukaryotic cell
(prokaryotes just have DNA in the cytoplasm)
• Q2 - Made up of DNA (that is wrapped around
protein), genes and alleles.
• Q3- Chromosomes are an “X” shape in
metaphase (of mitosis). They are a cylinder
after mitosis.
• Q4- DNA is in the shape of a double helix.
(see pipe cleaner model).
DNA structure
• Q4 - It is wound in a double helix. (sugars and
phosphates making the “ladder” and
nitrogenous bases making the “rungs”)
• Rosalind Franklin’s crystallography structure
pictures of DNA helped Watson and Crick
determine that DNA was a double stranded
helix.
• DNA in one cell stretched out straight = about
59 inches. (5 feet tall!)
Metaphase chromosome
Traits
• Q5 - Traits are caused or “coded” by:
– RNA and proteins
– Genes (such as eye color)
– Alleles (a specific form of a gene such as blue or green
eyes)
• Q6- individuals have 2 alleles (one from each parent)
for each gene.
• Q7 – allele – a single gene, such as blue eye color.
• Q8- Genotype – the specific alleles one individual has
for one gene (usually designated by two letters) or
many genes.
For homework – to help you be able to make phenotypes from
genotypes and be able to determine an off-spring’s genotype
when given parental genotypes.
For help with questions 9 and 10 on study guide.
• 1. Do the 5 (practice mode) “Larkey offspring Genotype and
Phenotype” activity and PRINT OUT with your name class and
student # on it.
• 2. Use the Larkey Punnett Square practice 5 times to ensure your
understanding of possible ratios – nothing to print out here.
• 3. Use the Larkey “Impossible Traits” (practice mode) activity and
PRINT OUT with your name class– and student # on it. * if you
miss a lot the first time, redo until you have better understanding
(and/or come get help if you need it).
More vocab – q11
• Dominant – a form of a gene that is expressed as
a trait whenever it is present (in one copy or two
copies – homozygous or heterozygous)
• Recessive – a form of gene that is expressed as a
trait only when it is present in two copies (bb for
blue eyes)
• Codominant – A trait that is influenced by two
different alleles for the same gene (red and white
flowers make pink, or AA and BB blood type make
AB)
Who was Mendel?
• Gregor Mendel (1822-?) in Czech Republic in
central Europe.
• Researched at a monastery because too poor
for schooling.
• Famous for breeding pea plants and learning
some key genetic facts.
4 important things Mendel learned –
Q13
•
•
•
•
Two factors (alleles) determine some traits.
One allele comes from each parent.
Factors (alleles) can be dominant or recessive.
(Recessive alleles can be present without
being seen – no representation in the
phenotype)
More details – can read on your own - Through
creating F1 and F2 peas, Mendel learns:
• Mendel then let the F1 self pollinate to create the
F2 generation.
• Mendel learned that tall was a dominant trait or
allele in pea plants. (Tt and TT are both tall).
• He also learned that the short trait didn’t
disappear completely but showed up again in the
F2. The short trait or phenotype is recessive to
the tall trait. (only tt will be short).
• Height in the pea plant was controlled by 1 gene.
Mendel’s yellow and green pea pods
• Mendel’s genetic hypothesis explained how
traits could disappear in one generation and
appear in the next.
• Mendel’s ratios were easily represented by
Reginald Punnett who introduced Punnett
squares.
After Mendel’s discoveries
• Virtually ignored for about 35 years.
• 1875 Chromosomes were observed inside a
nucleus.
• When cells are going to divide (one cell into 2
cells), the chromosomes first duplicate
themselves.
• Humans have 46 chromosomes (23 pairs).
Famous genetic scientists – Q12+ Q 14
• 1902 Walter S. Sutton coined the term
homologues for nearly identical pairs of
chromosomes (homologous chromosomes)
– Homologous chromosomes are the same size and
similar structure. In their structure homologous
chromosomes have the same genes in the same
sequence but do not necessarily the same allele of
each gene. – we have them because each parent
donated one of each chromosome.
More scientists – Q12
Early 1900s - Reginald Punnett developed the
Punnett square to determine the probability of
the F1 generation “children” having different
alleles
1930 Phoebus A. Levene determined that DNA was
made up of 3 main parts (phosphate, sugar, and 4
nitrogenous bases – A,T,G,C)
More famous genetic scientists – Q 12
• (May 1952) Rosalind Franklin –
– Took crystalline x-rays of DNA which
helped to determine its shape eventually.
• (Late 1952) Watson and Crick –
– speculated that DNA is in the form of a double
helix – later confirmed.
This discovery allowed much more to be
learned about DNA.
Cell cycle – part of Q15
M is mitosis, G1 is growth phase one, S is DNA synthesis phase, G2 is growth
phase 2
Cell cycle – different picture
Mitosis
Q15 Mitosis
• Q 15 - Mitosis – the division of genetic material
when a single cell divides into 2 cells.
• Q 15 - Cells must undergo mitosis because old
cells die and each new cell must have its own
copy of DNA.
• When “normal” cells divide they first make copies
of their chromosomes (2n becomes 4n).
• Then the cell goes through the steps of mitosis.
• During mitosis the cell goes through interphase,
prophase, metaphase, anaphase, telophase and
cytokinesis.
BIG picture - Mitosis cont
• During mitosis normal cells reproduce their
DNA and then divide it in half, with each half
going to separate cells.
• One cell becomes two cells with the exact
same copy of DNA in each cell.
Human chromosomes (23 pairs)
Meiosis
• Q18 – meiosis is the division of one (2n) cell
into 4 sex cells (1n) that have only ½ the
genetic material.
•
• Q19 – meiosis happens for the purpose of
reproduction.
– (so that we don’t continue to get more and more
chromosomes every generation (if mom 2 of each
chromosome and dad gave 2, that would make 4
copies, and then 8, 16, etc. for the purpose of
reproduction.
More meiosis
When sex cells (sperm and egg in humans) are created they
are created through meiosis.
1 cell copies it’s DNA (becomes 4n) and then divides twice to
create 4 cells with 1 copy of genes each.
When two sex cells (sperm and egg) come together they
each bring one copy and once again make an individual with
homologous chromosome pairs. (2n)
What are chromosomes made of?
• 19 - Chromosomes are made up of DNA
(deoxyribonucleic acid).
• 20 - During the 1930s Pheobus Levene
analyzed DNA and found it is made of:
– Phosphate
– Sugar (ribose)
– 4 nitrogenous bases (A, T, G, C)
– Adenine, thymine, guanine, and cytosine
DNA
• Why is DNA important?
– It codes for all of the proteins in your body!
• Q21 - DNA makes RNA which makes protein.
• Q 22 – DNA doesn’t make proteins directly because it is
too easy to mutate (which can cause cancer).
• Q24 Why are proteins important?
– Proteins cause or help speed up every reaction that is
happening in our bodies.
– Proteins are structural.
– We could not live without proteins or DNA.
Alleles
• Homozygous – copies of two of the same
allele, aa or AA.
• Heterozygous – one cope if two different
alleles such as Aa.
Extra credit:
• DNA to RNA to protein
• DNA creates RNA (transcription) in the
nucleus – through the enzyme RNA
polymerase.
• RNA creates protein in the cytoplasm on a
ribosome (either free floating or attached to
the endoplasmic reticulum)
Homologous chromosomes
• Why not identical chromosomes?
• (they have genes for all of the same traits, but
one gene on one chromosome – called an
allele may code for blue eyes and the
chromosome from the other parent might
code for green eyes.)
• *** Homologous chromosomes have identical
traits but not necessarily identical alleles.
Chromosomes before and after mitosis
genes
• Genes are made of DNA.
• Genes cause our traits.
• If we have 2 copies of the same trait (Larkey has
AA for short legs) it is said the organism is
homozygous for that trait.
• If we have one of each possible allele, the
organism is heterozygous for that trait.
• Size of a gene (few hundred base pairs, to 2.4
million base pairs! – avg human gene 3,000 base
pairs)