FCH 532 Lecture 1: intro to DNA and
genetics
Webpage:
http://www.esf.edu/chemistry/nomura/fch532/
Genetics review
Chapter 1
Figure 2.1 The storage and
replication of biological
information in DNA and its
transfer to RNA to
synthesize proteins that
direct cellular function.
Molecules that carry cellular
information/instructions:
1. DNA
2. RNA
3. Proteins
4. Carbohydrates
5. Lipids/fatty acids
Expression and Transmission of
Genetic Information
• Deoxyribonucleic acid (DNA) is the master
template for genetic information.
• Consists of two strands of linked nucleotides
• Nucleotides are composed of
– Deoxyribose sugar
– Phosphoryl group
– One of four bases: Adenine (A), Thymine (T),
Guanine (G), or Cytosine (C).
• Genetic information is encoded in the sequence of
the nucleotides.
Figure 1-16 Double-stranded
DNA.
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•Each DNA base is hydrogen
bonded to a base on the
opposite strand forming a base
pair.
•A bonds with T and G bonds
with C forming complementary
strands.
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Figure 1-17 Schematic diagram
of DNA replication.
•The division of a cell must be accompanied by
replication of DNA
•Enzymatically catalyzed
•Each DNA strand acts as a template for its
complementary strand.
•Each progeny cell has one parental strand
and one daughter strand.
•Mutations occur in copying errors or damage to
a parental strand-causes one or more wrong
bases to be incorporated into the daughter
strand
•Most mutations are innocuous or
deleterious.
Expression of Genetic Information
• Expression of genetic information takes place in
two-stages.
• Stage I: Transcription: DNA strand serves as a
template for the synthesis of a complementary,
single-strand of ribonucleic acid (RNA). RNA has
ribose instead of deoxyribose (Ch 5) and uracil (U)
replaces thymine (T).
• Stage II: Translation: Ribosomes translate the RNA
sequence to enzymatically assemble amino acids to
form polypeptides.
DNA  RNA  Protein
Cells store genetic information in
double-stranded DNA
• Double-stranded DNA is the carrier of genetic
information in all cells and most viruses.
• Viruses are extracellular packages of genetic
information-can store their genetic information in
double-stranded DNA, double-stranded and singlestranded RNA, and single-stranded DNA.
• Cellular DNA duplexes are organized into
chromosomes.
Circular chromosomes
• Procaryotic chromosomes contain a single circular
DNA duplex.
• Procaryotes are haploid (1N) meaning that they
have a single copy of their genetic information.
• Many procaryotes also have small, autonomous,
circular DNA duplexes called plasmids.
• Chromosomal DNA is complexed with basic proteins
and RNA molecules that fold it into a semicondensed state (nucleoid).
• Mitochondrial and chloroplast DNAs are also
circular.
Linear chromosomes
• Eucaryotic genomes are composed of several linear
DNA duplexes that are organized into several
chromosomes within the nucleus.
• Consist of long continuous DNA molecule
associated with small basic proteins called
histones.
• In eukarotic cells, there are normally two copies of
each chromosome (homologous pairs) in every
somatic cell.
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Figure 1-18
Chromosomes.
Eukaryotic cells
• Realization that all organisms are derived from
single cells set the stage for the development of
modern biology.
• Germ cells (sperm and ova) are directly descended
from germ cells of the previous generation.
• Somatic cells (all other cells) are derived from
germ cells but do not give rise to them.
• Most eukaryotes are diploid (2N) meaning they
have two homologous sets of chromosomes, one
from the female parent and one from the male
parent.
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Table 1-2
Number of Chromosomes (2N) in Some
Eurkaryotes.
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Figure 1-19 Mitosis, the usual form
of cell division in eukaryotes.
•Somatic cells divide by
mitosis.
•2N duplicates to 4N and
results in two daughter cells
with 2N
•During cell division, each
chromosome attaches by its
centromere to the mitotic spindle.
•Members of each are pulled to
opposite poles of the dividing cell
by the spindle to yield diploid
daughter cells.
Figure 1-20
Meiosis, which leads to the
formation of gametes (sex cells).
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•Germ cells are formed by meiosis.
•Requires 2 cell divisions.
•Before the first meiotic division, each
chromosome replicates but the resulting
chromatids are attached to the centromere.
•Recombination can occur between sections
of homologous chromosomes during
metaphase I (crossing-over).
•Results in four haploid cells (gametes).
Genetics and inheritance
• 1st reported by Gregor Mendel in 1866, he analyzed a series
of genetic crosses between garden peas.
• Characterized differences in physical traits: seed shape (round
vs. wrinkled), seed color (yellow vs. green) or flower color
(white vs. purple).
• Findings: crossing parents (P generation) with two different
traits results in progeny (F1-first filial generation) that are
similar to one of the parents.
• The trait appearing in the F1 generation is considered to be
dominant and the alternate trait is said to be recessive.
• If the F1 generation are crossed the resulting F2 generation
are 3/4 dominant and 1/4 recessive.
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Figure 1-21 Genetic crosses.
Genetics and inheritance
• If the F2 generation with the recessive traits are crossed,
all of the progeny will show the recessive trait.
• The F2’s showing a dominant trait fall into 2 categories:
1/3 breed true, whereas the remaining 2/3 fall into the
same 3:1 ratio of dominant to recessive traits.
• These are accounted for from genes with alternative
forms (alleles).
• Each plant has a pair of genes that code for each trait.
One gene each is inherited from each parent.
• Example RR for round seeds and rr for wrinkled seedsgenotypes.
• These are called homozygous for seed shape in
genotype.
• Plants with the Rr genotype are heterozygous for seed
shape and have the round phenotype.
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Figure 1-22 Genotypes and phenotypes.
Figure 1-23 Independent
assortment.
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•Some different traits are
independently inherited.
•Here 2 sets of alleles are
responsible for the phenotypes: R
for round, r for wrinkled, Y for
yellow, and y for green.
Figure 1-24 Codominance.
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•Some instances when the
dominance of both traits are
equal.
•In snapdragons a pure red (AA)
is crossed with a pure white (aa)
to yield and F1 generation that is
pink (Aa).
• Crossing the F1 generation
results in a 1:2:1 ratio of
red:pink:white.
•Codominance.
Figure 1-25 Independent
segregation.
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•Chromosomal theory of
inheritance-genes are parts of
chromosomes.
•First trait to be assigned
chromosomal location: sex
•Females: 2 copies of the X
chromosome (XX).
•Males have the Y chromosome
(XY).
•Explains the 1:1 ratio of males to
females in most species.
•X and Y chromosomes are
referred to as sex chromsomes.
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Figure 1-26 The fruit fly Drosophila melanogaster.
•Produce new generation every 14 days so genetic crosses can be seen
faster than with peas.
•1st mutant strain had white eyes instead of red eyes of the wild type
(occuring in nature). Through genetic crosses it was shown that the white
eye gene (wh) parallels the X chromosome. This means the wh gene is
located on the X chromosome and the Y chromosome does not contain it.
•Sex linked chromosome.
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Figure 1-27
Crossi
ng-over.
•Genes that are on the same
chromosome do not sort
independently.
•However, linked genes
recombine (exchange relative
positions with their allelic
counterparts on homologous
chromsomes) with a certain
characteristic frequency.
•Occurs in the start of meiosis
(metaphase I)
•Can be used to map relative
positions on different
chromosomes.
Figure 1-28 Portion of
the genetic map of
chromosome 2 of
Drosophilia.
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•Two genes separated by m map
units recombine with a frequency
of m%.
Nonallelic genes complement one
another
• To examine whether or not 2 recessive that traits
affect similar functions are allelic (different forms of
the same gene) you can do a complementation
test.
• Homozygotes for both traits to be tested are
crossed to each other.
• If the traits are nonallelic, the progeny will have the
wild-type phenotype since the two genes
complement one another.
• If not, then the genes are allelic.
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Figure 1-29a The complementation test indicates
whether two recessive traits are allelic. (a) Crossing a
homozygote for purple eye color with a homozygote for
brown eye color.
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Figure 1-29bThe complementation test indicates
whether two recessive traits are allelic. (b) Crossing a
female with white eye color gene with a male with
coffee eye color gene.