Download GENETICS

GENETICS
INHERITANCE AND CONTINUITY
Genes (instructions)
 A set of chemical instructions that determines an
organism’s features and characteristics.
 Passed from parents to offspring during
reproduction in the form of DNA (chemical code).
 Genes can be changed through recombination,
mutation, and genetic engineering.
Historical Genetics
Gregor Mendel
 Austrian Monk in the 1850’s worked with garden
pea plants and developed the basic principles of
heredity.
 Cross-pollinated plants with contrasting features
and mathematically analyzed large numbers of
offspring.
 He proposed that pea plant’s characteristics were
inherited as a result of the transmission of gene
determiners. He wasn’t aware of “genes” or
“chromosomes”.
 He is noted for:
- Dominance
- Segregation
- Independent Assortment
Basics Of Genetics
Genes
 Exist at definite loci (permanent locations) on
chromosomes.
Alleles
 Two genes for every characteristic. One gene
comes from the father and one gene comes from
the mother.
Homologous Chromosomes
 Allelic pair of genes of the same characteristic
on the same chromosome.
Human Genome (year 2000)
 30,000 genes spread over 23 pairs of
chromosomes. 15,000 from the mother and
15,000 from the father.
 1,000 DNA units on a single gene. 3.2 billion
DNA units in total.
 Location and kind of gene is identified. A 10
year project.
Diagram of a Chromosome
Gene-Chromosome Theory
 Genes exist at certain locations on chromosomes.
Dominance
 When only one of the genes of an allele pair is
expressed (shown) for a particular feature.
 The dominant gene masks the other gene
characteristic.
 Appear more frequently in a population.
 Symbolized by a capital letter.
Recessive
 The gene that is present but not expressed. Two
recessive genes are needed for the expression of
a particular feature.
 Appear less frequently in a population.
 Symbolized by a lower case letter.
Gene for height in pea plants is written:
T – Tall pea plants, dominant
t – short pea plants, recessive
Tall pea plant genes are found in two ways:
TT – homozygous dominant, purebred
Tt – heterozygous dominant, hybrid
Short pea plant genes are found in one way:
tt – homozygous recessive, purebred
Genotype
 Genetic make up of a characteristic.
 TT, Tt, or tt for height of pea plants.
Phenotype
 Physical appearance of a gene for that
characteristic.
 Tall or short for height.
F1 Generation (Filial)
 Resulting offspring from parents of first cross of
genes.
F2 Generation (Filial)
 Offspring resulting from the cross between
members of the F1 generation.
Punnet Square Method Of Crossing Genes
Genotype:
Phenotype:
Genotype:
Phenotype:
Genotype:
Phenotype:
Segregation and Recombination
 Separation of homologous chromosomes during
meiosis (segregation).
 Recombination of genes during fertilization.
 New genetic varieties occur from recombination.
Diagram of Segregation and Recombination
Incomplete Dominance




Traits are not clearly dominant or recessive
Features are a result of a blend.
Pink Snap-Dragons.
Offspring should be 3:1 phenotype (3 red, 1 white)
but tend to be 1:2:1 phenotype (1 red, 2 pink, 1
white).
Co-Dominance
 Expression of two dominant alleles. Both features
show up in an organism.
 Roan cattle. Equal distribution of red and white
hair.
 Red hair is dominant.
 White hair is dominant.
Sickle cell anemia is a co-dominant inheritance.
Multiple Alleles
 A, B, and O blood types are an example of
expression of “3” alleles.
 Type A and B are co-dominant.
 Type O is recessive to A and B.
Sex Determination
 XX female
 XY male
 Sex of offspring is determined at fertilization by
male parent.
 Always a 50% chance for a boy or a girl.
Gene Linkage
 Genes of 2 different traits are located on the
same chromosome pair.
 Linked and inherited together.
 Red hair and freckles.
 Black hair and brown eyes.
Sex Linkage
 Genes for certain traits are on the “X”
chromosomes and do not have corresponding
alleles (genes) on the “Y” chromosome.
 Many of these genes are recessive.
 Expressed more in males due to having only one
“X” chromosome. They only need one recessive
gene for expression of the trait.
 Female is carrier for the same gene if she is hybrid
recessive.
 Hemophilia and color-blindness are sex linked.
Material Of Genetics
 Characteristics are determined by inherited genes
and their expression can be modified by their
interaction with the environment.
DNA Structure
 Deoxyribonucleic acid replicates itself and is
passed from generation to generation.
 Controls cellular activity by influencing the
production of enzymes.
 Found in the nucleus of cells.
Watson-Crick Model
 Used to explain the principle action of genes.
 Genes act in two basic ways:
1. Maintain genotype from generation to generation
by replication of genetic code.
2. Control cellular activity by controlling the
production of enzymes which determine
phenotype.
Nucleotides
 DNA is made up of thousands of smaller
repeating units
 Composed of 3 parts:
1. Phosphate group – oxygen, hydrogen,
phosphorus.
2. Deoxyribose – 5 carbon sugar.
3. Nitrogen Base – total of 4
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
 Nucleotides pair up with their nitrogen bases.
 A-T combo and C-G combo.
 A twisted ladder is formed – “Double Helix”.
1. Uprights are composed alternating phosphate and
deoxyribose groups.
2. Each rung is composed of a pair of nitrogen
bases.
DNA Replication
 Self-duplication of genes by DNA replication
during mitosis and meiosis.
 Double stranded DNA “unzips” along weak
hydrogen bonds between base pairs.
 Free nucleotides in the nucleus are attached to
the unwound strands of DNA, in sequence.
 Two new double strands of DNA are formed.
They are identical to each other and the
original DNA.
Gene Control Of Cellular Activities
 Involves DNA and RNA (ribonucleic acid)
 DNA provides the information to produce
specific enzymes to run the cell’s activities.
 RNA functions to carry this information from the
nucleus to the cytoplasm and helps in protein
production.
RNA like DNA contains nucleotide building blocks.
Three Major Differences Between DNA and RNA
1. Ribose is substituted for Deoxyribose.
2. Uracil (U) is substituted for Thymine (T).
3. There is a Single chain of nucleotides.
There Are Three Types Of RNA:
1. Messenger RNA (mRNA) – “carries” the DNA
message from the nucleus DNA to the ribosomes
(sites of protein synthesis).
2. Transfer RNA (tRNA) – “transfers” amino acids
to the ribosomes.
3. Ribosomal RNA (rRNA) – makes up the
“identification code” of each ribosome for specific
protein production.
Genetic Code
 Contains information for the sequence of amino
acids for a specific protein.
 Present in mRNA.
 RNA code is a Triplet Code (codon) having just
three nitrogen bases based on sequences of three
nitrogen bases in the DNA.
Protein Synthesis
 An enzyme and the characteristic it expresses is
dependent on its protein make-up.
 Enzymes control and coordinate all the cell’s
activities. Including growth, cell division, and
development.
 The type and function of enzymes a cell possesses
defines the individuality of a cell. DNA directs the
type of enzyme produced.
Steps Of Protein Synthesis
1. In the nucleus: DNA unzips and forms a
template for the synthesis of mRNA from free
nucleotides .
2. Moving out of the nucleus: mRNA carrying a
specific code from the DNA template move to
ribosomes in the cytoplasm.
3. At the site of ribosomes: Translation occurs.
rRNA temporarily binds mRNA to the
ribosomes. A specific protein will be made.
4. In the cytoplasm: tRNA (anticodons) pick up
specific amino acids.
5. A the site of ribosomes: tRNA bond to a
particular codon. Amino acids attached to tRNA
are bonded in sequence to the base sequence of
mRNA. Protein (peptide) chains are formed
from this sequencing.
Interaction Of Heredity And Environment
 Environment interacts with genes in the
development and expression of inherited traits.
Examples:
 Effect Of Light On Chlorophyll Production – in
the presence of light the plant makes
chlorophyll, turn green, and carry on
photosynthesis. Without light most plants only
produce a yellow pigment.
 Effect Of Temperature – on hair color in the
Himalayan rabbit. Hair is normally white in
warm climates. In Artic climates, paws are black
where body is in continual contact with cold
surface. Ice applied to the body causes hair to
turn black.
 Identical Twin Studies – identical twins with the
same DNA should develop in the same identical
manner. However, identical twins often shoe
changes in their phenotype as they mature.
Changes are dependent on the environment.
Genetic Applications
 Gene Mutations – any change in the base
sequence of DNA. Include the addition or
deletion of bases in the DNA sequence or the
substitution of one base for another.
 When it occurs in the sex cells the mutation is
passed on.
 When it occurs in a body cell the mutation can
multiply in the organism but its not passed on.
 Most occur spontaneously.
Examples:
1. Chromosome Alteration in number and structure.
During disjunction of meiosis. Pair of sister
chromatids fail to separate. Zygote often dies.
Down’s Syndrome can occur (extra chromosome
on the 21st pair. Polyploid is common in plants.
Offspring get an extra whole set of
chromosomes. Larger and more vigorous plant
but seedless (watermelon, cucumbers).
2. Turner’s Syndrome – only one sex chromosome
in cells. Female is underdeveloped in sexual
characteristics.
3. Klinefelter’s Syndrome – 2X’s and a Y in each
cell. Male is underdeveloped in sex organs.
4. Albinism – loss of eye pigment due ton random
change in chemical nature of DNA.
Genetic Research
 Cloning - producing genetically identical offspring
from the body cells of an organism.
1. Plants with desirable qualities can be rapidly
produced from the cells of a single parent.
2. Cloning combined with genetic engineering has
produced pigs, cows, and sheep that make
therapeutic proteins.
 Genetic Engineering - new genes can be
transferred from one organism to another,
resulting in the formation of Recombinant DNA.
The cell can then make the chemical coded for by
these new genes.
1. Bacteria have been genetically engineered to make
hormones for hormonal deficiencies and diabetes.
Human growth hormone and interferon have also
been made in this manner. Interferon is used for
treating auto-immune diseases. Aspartame
(Nutrasweet), an artificial sweetener, and nail
polish remover (acetone) are both made in the
same manner.
Medical Genetic Research
Genetic Counseling
 Discussions between Doctor and Family on
probability of inheritance patterns, predictions of
genetic disorders, and family planning.
 Genetic Disorders can be detected before or after
birth.
 Genetic disorders can be detected through genetic
counseling or by:
1. Screening – chemical analysis of blood or urine
that may indicate the presence of chemicals related
to the genetic disorder.
2. Karotyping – a photograph showing paired
homologous chromosomes from a cell. May show
a missing or extra chromosome.
3. Amiocentesis – removal of amniotic from the fetus
for chemical and/or cellular analysis. Chromosome
content of the cell can be seen. Down Syndrome
may be identified by this technique.
Selective Breeding
Artificial Selection
1. Inbreeding and hybridization (cross breeding) is
used to produce and maintain desirable traits.
 Breeders of dogs, cattle, and horses often use this
technique.
 Seedless oranges, apple varieties, and hybrid roses
are produced in this manner.
Vegetative Propagation
 Maintenance of desirable mutations.