Review of Literature
Do you know that by using your own DNA, you can trace your ancestry as far
back as thousands of years ago? It can be done using a process known as DNA
genotyping, which has many pros and cons. Today, many scientists have created
genotyping companies such as 23andMe and Illumina. These companies both genotype
individuals and create equipment necessary to the genotyping process. The kind of
information sent back to people who have been genotyped is known single nucleotide
polymorphisms in your DNA that define certain haplotypes. By knowing your own
haplotype, you are able to compare it to known populations that have been genotyped to
determine your ancestry. Also, DNA that has been collected from ancient human
remains has been genotyped over the years and put into genetic databases. All of this
information about genetics would not be possible without scientists such as Gregor
Mendel, Thomas Hunt Morgan, and many others. The scientists discovered many
different facts about genetics such as the DNA structure and they also defined what
alleles, haplogroups, and haplotypes are.
The history of genetics began with a time period known as the spontaneous
generation. During this generation, “people believed that living organisms could
spontaneously arise from a non-living matter” (Gonick and Wheelis 20). Maggots
supposedly came from decaying meat, horsehair turned into worms, and frogs, mice, and
bugs were slime coming to life. Many people attempted to prove the spontaneous
generation wrong by experimenting on animals such as bugs, worms, flies, and maggots.
In the seventeenth century, Francesco Redi was one of the scientists to challenge the
Spontaneous Generation. Redi placed pieces of fresh meat in two jars. One jar had a cap
on the top tightly sealed and the other jar had no cap allowing anything to enter. After
time passed, maggots were only forming in the jar that had no cap on it. Redi’s
experiment proved that maggots only form from flies, not meat. Even though Redi
proved the spontaneous generation false, people continued to believe that the generation
was true (Gonick and Wheelis 20-23).
Some of the scientists who are very important in the history of genetics are Anton
Leevwenhoek, Camerarius, Thomas Hunt Morgan, Francis Crick, James Watson, and
Maurice Wilkins. Anton Leevwenhoek was the first scientist to make use of the
microscope. Anton followed life histories of many small organisms such as fleas. By
tracing the life histories, he found that fleas are sexual beings just like dogs and cats.
Anton also discovered bacteria, which is very important today in the researching of
genetics. One other important aspect in genetics that Anton discovered is the existence of
sperm cells. By examining the semen, he saw millions of sperms. Anton believed that
each sperm contained a small organism inside, which is false but lead to further study by
other scientist to discover sperms’ key role in reproduction. Another scientist that is
important in the history of genetics is Camerarius. He proved flowers contain organs
similar to animals’ reproductive organs. The process of discovering this included
studying the anthers and stigma. This showed that pollen from the anthers penetrated to
the ovary causing seeds to develop. The third scientist who is very important in the
history of genetics is Thomas Hunt Morgan. Thomas was a biologist, geneticist,
embryologist, and a science author. Because he made important discoveries with the
chromosomes’ role in heredity, Thomas won a Nobel Prize in Medicine in 1933 (Gonick
and Wheelis 19-31). The scientists James Watson, Francis Crick, and Maurice Wilkins
won a Nobel Prize in physiology or medicine in 1953 for the discovery of the DNA
structure. These scientists found that DNA contains special structures that are needed for
producing proteins in a human. They also found that DNA contains two chains twisted
around each other, or double helixes. The four bases, Adenine, Thymine, Guanine, and
Cytosine hold the double helixes together (www.chemheritage.org). In conclusion, the
history of genetics includes the spontaneous generation and many important scientists
who studied many important aspects in genetics.
Another influential scientist in genetic history was an Augustan monk named
Gregor Mendel. Gregor Mendel lived from 1822 to 1884 in a monastery in Brunn,
Austria. In his spare time, Mendel bred pea plants in the garden of his monastery. He
crossed many different pea plants with various results. Medel observed that pea plants
with round and wrinkled seeds produced a round seeds; a yellow and a green seed,
produced a yellow seed and a red and white flower produced a red flower. These
crossings led to the discovery of dominant against the recessive traits. For example,
Mendel crossed the red and white flower and the resulting offspring yielded a red flower.
The red flower was dominant over the recessive white flower so the offspring carried the
red trait. This is called dominance, or a trait that does not hide in the alleles when a
recessive trait is present. Heredity also includes recessive traits, incomplete dominance,
and co-dominance. A recessive trait is a trait that is masked when a dominant allele is
present. Incomplete dominance is when neither trait is dominant because the offspring is
totally different from its parents. Co-dominance is when the offspring is a mixture
between the parents. For example, a red and white flower’s off spring that is both red and
white is co-dominant because neither trait is recessive or dominant (McClean).
From his experimenting, Mendel made many conclusions and helped contribute
more knowledge to genetics. Mendel made two main conclusions from his experimenting.
The first conclusion he made is that “heredity determinants are of a particular nature.
These determinants are called genes” (McClean). The second conclusion Gregor made is
that each parent has a gene pair in every cell for the traits that were studied. From his
conclusions, Mendel made two main contributions to genetics. The fist contribution he
made is developing pure lines, or a population that truly breeds for a particular trait. This
is important because any non-pure generation would confuse the results of genetic
experiments. The second contribution to genetics that Mendel made is that he counted his
results and kept statistical notes for future proof and referral. His notes recorded the
results of breeding two different or the same pea plants. He also recorded the ratio of
those two plants resulting progeny. Then Mendel made his first law based on all of his
researching and experimenting. This law is known as the law of segregation. The law of
segregation states, “During gamete formation, each member of an allele separates from
the other member to form the genetic constitution of the gamete” (McClean). In
conclusion, Mendel is a very important person in the history of genetics and he has
experimented on pea plants, made conclusions form his experimenting, and then made
two main contributions to the field of genetics.
One other essential discovery in genetics is the structure and function of
DNA, or deoxyribonucleic acid. DNA is made up of four base pairs known as ATGC or
Adenine, Thymine, Guanine, and Cystine. Adenine and Thymine only pair together and
Guanine and Cystine only pair together. A group of three continuous bases known as
codons code for a very specific amino acid. There are twenty-six possible codon
combinations, but only twenty amino acids. Each amino acid is like a word in the English
language and the different bases that make up each amino acid are like a letter in the
alphabet. If one letter in a word is changed, it will have a whole new meaning. This is the
same for codons: if one base is changed it may code for a whole new amino acid. The
base pairs do not only form amino acids, they also help to form the DNA duplex. This
duplex is made up of a phosphate backbone, which contains a pentose sugar, a phosphate
base, and a phosphate group. Each duplex is able to replicate millions of times. This
process is known as DNA replication. In replication, two DNA strands unwind into two
distinct pieces. Then each of those two pieces replicates itself and winds back up linking
with the correct base along the way. When this process is completed, the DNA winds up
into a ball shape that is small enough to fit inside of the nucleus of a cell. One of the two
sex-determining chromosomes is the Y chromosome. This chromosome is composed of
fifty-eight million base pairs but surprisingly only makes up one percent of the DNA in
males (Bruce 867). The Y chromosome is passed on from father to son. The traits in the
chromosome are called holandric traits, which are used to trace the paternal side in
genetic genealogy. The second sex-determining DNA is mitochondrial DNA. The mother
only contributes this DNA to her daughter and son. It is located in the mitochondria of a
cell and is composed of sixteen thousand base pairs and codes for thirty-seven genes, and
that makes it the smallest chromosome (Bruce 850-854). In conclusion, DNA is a very
important aspect in the human body by coding for all of its essential components but it is
also essential to discovery your family history via genetic genealogy.
In genealogy, having the knowledge of what haplotypes and specific traits you
have is the cornerstone of understanding your ancestry. A haplotype is a combination of
alleles on a chromosome that is inherited all together. An allele is an alternate form for a
gene. It can either be dominant or recessive. When an allele is dominant it is fully
expressed. When it is recessive, on the other hand, it is the one gene that is completely
masked or blocked by a dominant allele (Bruce 839-840). One to two genes control most
alleles but three to four genes control others. If three to four genes control a trait, it is
called a polygenic trait. One example of a polygenic trait is skin color because three to
four genes, each of which has two alleles, control it. One other important part in
understanding genetics is knowing the difference between homozygous and heterozygous,
genotype and phenotype and male and female. Homozygous is when an organism’s two
alleles are the same, not different. Heterozygous is when an organism’s two alleles are
different, not the same. A genotype is an organism’s actual genetic makeup. For example,
and organisms alleles can be Ss, SS, or ss. A phenotype, on the other hand, is an
organism’s expressed traits, physical features, of how the genes are expressed physically
in a person. For example, some phenotypes of a person could be long blond hair or short
dark hair, tall height or short height, or brown or blue eyes. The difference between a
male and female is that a female has an XX chromosome and a male has an XY
chromosome (Carter). In conclusion, one essential part of learning genetics is
understanding what haplotypes and other specific traits mean.
Genetic genealogy is the study of DNA and it’s inheritance through many
previous family members and distinct populations. Scientists can trace a person’s
ancestry back many generations by analyzing DNA. There are four main uses of genetic
genealogy. First, genealogy helps people find their original ancestors’ origin and where
they are really from. Second, genetic genealogy allows people to trace their ancestors’
major migrations in their specific haplogroup. Third, genealogy helps people identify
their maternal and paternal lineages. Lastly, it helps people to find out specific
geographical location of their ancestors and how they lived and migrated throughout their
lifetime. Ancestry is a person’s family or ethnic past. It is very important to know your
ancestry in order to get to know yourself better. Many companies specialize in genetic
genealogy today. They help you to find out about your ancestors and at the same time,
identify your own specific haplogroup. DNA studies from genetic ancestry companies
show that everyone shares a common ancestor who lived in Africa many years ago. As
people migrated out of Africa, small mutations occurred in DNA. Each mutation is linked
to a specific ancestor at a specific time and place in history. These mutations tell a story
of our past (www.dnaancestryproject.com). To summarize, genetic genealogy uses DNA
to trace someone’s own ancestry and past.
Genotyping is the process of determining differences in the genetic makeup of a
person. It shows alleles a person has inherited, but it does not identify all of a person’s
genome. Genotyping only shows certain points on a person’s genome where a mutation
has occurred. Many people think genotyping and sequencing are the same process, but
they are very different. Genotyping identifies what variants a person has, it can be
preformed in various ways, and it is very cost efficient (Velarde). Sequencing, on the
other hand, shows the exact sequence of a certain length of DNA. It can be a short piece,
a long piece, a whole genome, or parts of a genome. Sequencing is also not as cost
efficient because it is analyzes more of a person’s DNA compared to genotyping.
Another benefit of a person having their DNA genotyped or sequenced, they can discover
if they are prone to a disease or illness. Doctors will then be able to be proactive and
instruct their patient on what to do in order to increase their wellness. This kind of gene is
called an actionable gene because people are able to take action with their disease or
illness. Your own genetic code has over six billion letters and it is what makes you
unique and the way you are (Holt).
Genotyping can have endless pros and cons but in the end, it makes a big impact
on people’s lives. The pros of genotyping include curing a person’s disease if it is caught
early enough, and it also allows that person to make the right decisions in their own
lifestyle. Also, genotyping allows people to become more aware of their own self and
past ancestral history. The cons of genotyping include affecting a person’s life negatively
if they discover they have a disease or illness that is incurable. This is why genotyping
and genetic interpretation should always involve medical counseling when it involves
health related discoveries. Also, if genotyping result is wrong and a person adjusts their
lifestyle accordingly it could lead to bad choices. Genotyping has made a great impact on
many people’s lives. For example, if you diagnose early a disease that can be cured or
managed you can positively impact the quality of your life. So they get to enjoy life even
longer with less worries of their sickness. Also, people become more aware of themselves
and where they came from. Therefore, people become confident in whom they are and
they adjust their lifestyle to fit their needs (Holt). In conclusion, genotyping has many
pros and cons and it is able to make a great impact on a person’s life.
Today, many genotyping companies are helping people become more aware of
their own genetics and what specific traits they possess. One major genotyping company
is called 23andMe. 23andMe will send a specimen tube to those who want to be
genotyped and the person will spit into it and send it back to their lab. At the lab, the
person’s saliva is genotyped and once the process it complete, the company will send the
person a username and password to 23andMe website. There, people are able to access
the results from their DNA being genotyped. The founders of 23andMe are Linda Avey,
Paul Cusenza, and Anne Wojcicki (Avey, Cusenza, Wojcicki). One other major
genotyping company is Illumina. Illumina develops, manufactures, and markets life
science tools. The company also sequences and genotypes genomes with their own
developed machines (Velarde). Both of the genotyping companies and many others go
through a very specific process. First, either a medical professional draws the patient’s
blood or the consumer spits into a specimen tube to collect saliva. The next day, the
blood or saliva arrives at a genotyping company. In the case of 23andMe the saliva is
processed and the DNA is sheered into fragments. Once that step is completed, the
laboratory places the sample on the genotyping chip which determines the genotypes of
your DNA in specific regions of interest such as health related alleles or haplotypes
associated with inheritance. The results from the testing are then sent back to the
individual (Holt). To summarize, many genotyping companies today are helping people
become more aware of their own genetics and what specific traits they possess.
The main reason to why people have their DNA genotyped or sequenced is
because they are worried that a bad mutation might have occurred within their body. A
mutation is a change of genes within a chromosome. Sometimes mutations can be bad
and the result will be a disease that will make things worse in a person’s body and life.
But, sometimes mutations can be good and the result will be even better than before and
possibly give benefits to the person in their daily life. For example, some mutations are
known to increase your resistance to certain viral infections or infectious diseases. Or, a
mutation can neither help nor harm a person. Instead, there is really no result from it.
Some mutations that can occur within someone include medical conditions caused by a
mutation in a protein, genetic disorders caused by mutations within the cell, and heredity
disease, which is caused by mutations in a germ cell. In conclusion, mutations can make a
person’s life worse, better, or do absolutely nothing to help or harm a person (Holt).
To summarize, tracing your ancestry can be done using a process known as DNA
genotyping, which has many pros and cons. Many modern day scientists have created
genotyping companies such as 23andMe and Illumina. Genotyping companies both
genotype individuals and create equipment necessary to the genotyping process. The kind
of information sent back people who have been genotyped is known polymorphisms in
your DNA that define certain haplotypes. By knowing your own haplotype, you are able
to compare it to known population studies to determine your ancestry. All of this
information about genetics would not be possible without scientists such as Gregor
Mendel, Thomas Hunt Morgan, and many others. The scientists discovered many
different facts about genetics such as the DNA structure and they also defined what
alleles, haplogroups, and haplotypes are. Each person can have his or her own unique
DNA genotyped and sequenced today thanks to all of the past studies in genetic history.