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.