Genetics is the science of heredity dealing with resemblances and differences between organisms resulting from gene interaction and environment. DNA contains the genetic code in chromosomes which are passed from parents to offspring during meiosis and fertilization, determining characteristics. Inheritance of single and multiple genes can be predicted using Punnett squares and determines traits like eye color, disease susceptibility, and more. Mutation and selection, whether natural or artificial, can introduce variation that natural selection acts upon over time.
2. Definitions
• Genetics is the science of heredity, dealing with
resemblances and differences of related organisms
resulting from the interaction of their genes and the
environment.
• Most of our characteristics as humans are determined
by our genes as they interact with the environment.
• Being products of sexual reproduction we obtain
characteristics from both of our parent. These
characteristics are coded by our parents’ genes, which
they transfer to us via gametes. This is called
inheritance.
3. DNA
• “Short for deoxyribonucleic acid. The nucleic acid that is the genetic
material determining the makeup of all living cells and many
viruses. It consists of two long strands of nucleotides linked
together in a structure resembling a ladder twisted into a spiral.” –
thefreedictionary.com
• deoxyribonucleic acid: an extremely long macromolecule that is the
main component of chromosomes and is the material that transfers
genetic characteristics in all life forms, constructed of two
nucleotide strands coiled around each other in a ladder-like
arrangement with the sidepieces composed of alternating
phosphate and deoxyribose units and the rungs composed of the
purine and pyrimidine bases adenine, guanine, cytosine, and
thymine: the genetic information of DNA is encoded in the
sequence of the bases and is transcribed as the strands unwind and
replicate. dictionary.reference.com
4. DNA
• DNA consists of a series of bases which can form a code.
• Three bases form a specific sub-code and codes for a specific
amino acid. This group of three bases is call a Codon.
5.
6.
7. Chromosomes
• A structure within the cell [nucleus] that bears the genetic
material as a threadlike linear strand of DNA bonded to
various proteins in the nucleus of eukaryotic cells. biology-
online.org
• A long thread- like structure containing one molecule of DNA
and binding proteins.
8. Chromosomes
• Each cell within an organism’s body contain the same number of
chromosomes, except the gametes.
• This standard number of chromosomes is called the Diploid Number (2n). For
humans the diploid number equals 46.
• Since we have two parents, we obtain half our chromosomes (via their gametes)
from each parent. The gametes therefore have half the diploid number of
chromosomes.
• This standard number of chromosomes is called the Haploid Number (n). For
humans the diploid number equals 23.
Egg(n) Sperm(n)
Zygote(n)
9. Genes
• A unit of heredity that is transferred from a parent to
offspring and is held to determine some characteristic of
the...: "proteins coded directly by genes.“ -
dictionary.reference.com (dr.com)
• A distinct sequence of nucleotides forming part of a
chromosome. - dr.com
• The Section of a DNA which codes for a specific type of
characteristic or protein.
10. Meiosis and Mitosis
• In order for an organism to grow, develop and
multiply cells must divide.
• There are two main types of cell division:
Mitosis and Meiosis.
• Mitosis is used for growth, repair and asexual
multiplication(reproduction).
• Meiosis is used for sexual reproduction.
11. Meiosis and Mitosis
• Mitosis
– Purpose:
The purpose of mitosis is to create new body cells for
growth and repair.
– Properties
• Two new cells are produced.
• Identical number of chromosomes as the parent cell.
14. Meiosis and Mitosis
• Meiosis
– Purpose:
The purpose of meiosis is to create gametes (sex cells)
for sexual reproduction.
– Properties
• Four new cells are produced.
• Half the number of chromosomes as the parent cell.
17. Introduction to Inheritance
• Inheritance deals with the passing on of characteristics from parent to
offspring. This is done by genes which are stored in chromosomes.
• Here are some definitions that are key to understanding inheritance.
Alleles alternate forms for genes. Remember that the gene for one
characteristic may have a variety of forms to code for the different traits.
For example the gene for tongue-rolling has to forms (alleles) the tongue
rolling allele and the non- tongue-rolling allele.
Dominant Allele: the one that’s fully expressed when the two alleles are
present; symbolized by a capital letter, often the first letter of the word
for which it stands. Eg: The tongue-rolling allele is dominant and is
usually represented by ‘R’.
Recessive Allele: the one that’s completely masked when the two allele
are present; symbolized by the SAME letter, but lower case. Eg: The non-
tongue-rolling allele recessive and is usually represented by ‘r’.
18. Introduction to Inheritance
Now remember that each individual has two genes for each for
every characteristic.
Homozygous: an individual has a pair of two of the same allele.
Eg: RR or rr.
Heterozygous: an individual has a pair of two different alleles. Eg:
Rr.
Genotype: the organism’s actual genetic make-up. Eg: For tongue
rolling there are three(3) possible genotypes – RR (Homozygous
Dominant), Rr (Heterozygous) and rr (Homozygous Recessive)?
Phenotype: the organism’s physically expressed traits as an
interaction between its genotype and the environment – what it
looks like, etc; how the genes are expressed. Eg: The ability to roll
one’s tongue – RR = tongue rolling; Rr = tongue rolling; and rr =
non-tongue rolling.
19. Introduction to Inheritance
• Inheritance has two basic phases:
i. Meiosis: the passing of one of each type of gene to
the gametes.
ii. Fertilization: the meeting of one gene from each
parent to form a total of two of type.
• Though thousands of genes are passed on, it is very
difficulty to study them all at the same time. So few
genes are considered at a time.
• Mono hybrid crosses deals with the consideration of
the inheritance of a single gene.
• Di hybrid crosses deals with the consideration of the
inheritance of a two genes.
20. Introduction to Inheritance
• The diagram below shows one of the possible
inheritance of the tongue-rolling gene.
Parents’ Genotype Gametes Offspring’s Genotype
Meiosis Fertilization
RR R
Rr
R
Rr
r
21. Mono-Hybrid to Inheritance
• Crosses are used to determines the possible
genotypes and phenotypes of offspring or
even parents.
• They are usually done with a flow chart or
Punnett square.
• Example & Exercises.
22. Codominance
• Codominance occurs when one both allele are
expressed in the phenotype.
• No gene is dominant and therefore the
phenotype is a mixture of the to pure phenotype.
Eg: in certain flower the gene for petal colour
expresses codominance. If R is the gene for red
petals and W for white the genotypes and their
corresponding phenotypes are – RR = red
petals, WW = white petals and RW = pink petals.
• Example & Exercises.
24. Sex Determination and Sex Linked
Genes
• Sex is determined by the pair of sex chromosomes called the X and
Y chromosome pair.
• XX = Female and XY = Male.
• The Y chromosome is shorter than the X and carries less genes so
some genes on the X has no matching genes on the Y.
• Males therefore carry only one gene for some genes found on the Y.
• Haemophilia is a gene found on the X but not the Y. Males therefore
carry one gene for haemophilia.
• Whereas females can be haemophiliac(hh), Non- Haemophiliac(HH)
or Heterozygous (Hh) (carrier); males can only be haemophiliac(h-),
Non- Haemophiliac(H-).
• Example & Exercises.
25. Mutation
• A Mutation occurs when a DNA gene is damaged or changed in such a way
as to alter the genetic message carried by that gene.A Mutagen is an
agent of substance that can bring about a permanent alteration to the
physical composition of a DNA gene such that the genetic message is
changed.
• Once the gene has been damaged or changed the mRNA transcribed from
that gene will now carry an altered message.
• The polypeptide made by translating the altered mRNA will now contain a
different sequence of amino acids. The function of the protein made by
folding this polypeptide will probably be changed or lost. In this example,
the enzyme that is catalyzing the production of flower color pigment has
been altered in such a way it no longer catalyzes the production of the red
pigment.
• No product (red pigment) is produced by the altered protein.
• In subtle or very obvious ways, the phenotype of the organism carrying
the mutation will be changed. In this case the flower, without the pigment
is no longer red.
26. Mutation
Mutagens
• Chemical Mutagens change the sequence of bases in a DNA gene in a number of ways; mimic the
correct nucleotide bases in a DNA molecule, but fail to base pair correctly during DNA replication.
• remove parts of the nucleotide (such as the amino group on adenine), again causing improper base
pairing during DNA replication.
• add hydrocarbon groups to various nucleotides, also causing incorrect base pairing during DNA
replication.
• Radiation High energy radiation from a radioactive material or from X-rays is absorbed by the
atoms in water molecules surrounding the DNA. This energy is transferred to the electrons which
then fly away from the atom. Left behind is a free radical, which is a highly dangerous and highly
reactive molecule that attacks the DNA molecule and alters it in many ways.
Radiation can also cause double strand breaks in the DNA molecule, which the cell's repair
mechanisms cannot put right.
• Sunlight contains ultraviolet radiation (the component that causes a suntan) which, when absorbed
by the DNA causes a cross link to form between certain adjacent bases. In most normal cases the
cells can repair this damage, but unrepaired dimers of this sort cause the replicating system to skip
over the mistake leaving a gap, which is supposed to be filled in later.
Unprotected exposure to UV radiation by the human skin can cause serious damage and may lead
to skin cancer and extensive skin tumors.
• Spontaneous mutations occur without exposure to any obvious mutagenic agent. Sometimes DNA
nucleotides shift without warning to a different chemical form (know as an isomer) which in turn
will form a different series of hydrogen bonds with it's partner. This leads to mistakes at the time of
DNA replication.
27. Artificial Selection
• Artificial selection is the intentional reproduction of individuals in a
population that have desirable traits. In organisms that reproduce
sexually, two adults that possess a desired trait — such as two
parent plants that are tall — are bred together. In this example, the
mechanisms of heredity dictate that the next generation will consist
of more tall plants than previous generations. If artificial selection is
continued, all of the population will ultimately be tall. Also called
selective breeding, artificial selection is perhaps best understood as
a contrast to natural selection, where the random forces of nature
determine which individuals survive and reproduce. In both cases,
the outcome is the same: a population changes over time, so that
certain traits become more common.
28. Artificial Selection
What are some examples of artificial selection?
• Teosinte (left) and its modern
descendent, corn, a product
of artificial selection
• Artificial selection has generated untold diversity in both plants and animals. In agriculture, superior strains of
corn, wheat, and soybeans have resulted from careful breeding. The Brassicas described by Paul Williams in the
video are great examples of artificial selection. Cabbage, broccoli, cauliflower, Brussels sprouts, collards, and kale
are all members of the same species, Brassica oleracea. Gardeners have cultivated flowers such as roses and
orchids, carefully manipulating heredity to produce the “perfect” hybrid.
• A variety of vegetables of theBrassica oleracea species
• Some consider domesticated animals to be the ultimate products of artificial selection. Thoroughbred racehorses
are one example of artificial selection of animals. The meats we eat are the result of the careful selective breeding
of cows, pigs, sheep, and chickens. Our pets are a far cry from their “wild” ancestors. Cats and dogs, which were
originally domesticated for pest control, hunting, or shepherding, eventually were bred to become companion
animals. A glance at a group of dogs — all of the species Canis familiaris — reveals an astounding diversity of body
type, size, and coloration.
• There can be a down side to artificial selection. Because this process essentially removes variation in a
population, selectively bred organisms can be especially susceptible to diseases or changes in the environment
that would not be a problem for a natural population. Inbreeding — the mating of closely related individuals — is
also a problem. In dogs, this has resulted in breeds that have health issues ranging from decreased life span to hip
dysplasia.
