Humans are 99.9% genetically identical and yet we are all so different. Even monozygotic twins have infrequent genetic differences due to mutations occurring during development and gene copy-number variation.

1. Human genetic diversity
&
Origin of major human groups
By Mayank sagar

2. Genetic human diversity
• Human genetic diversity are the genetic differences in and among
human population.
• Humans are 99.9% genetically identical and yet we are all so
different.
• There may be multiple variants of any given gene in the human
population, which leads to a situation called polymorphism.
• No two humans are genetically identical.
• Even monozygotic twins have infrequent genetic differences due to
mutations occurring during development and gene copy-number
variation.

3. • Full sequencing of human genomes has shown that in any given individual
there are, on average, close to 4 million genetic variants encompassing 12
Mb of sequence.New findings show that each human has on average 60
new mutations compared to their parents.
• Genetic Diversity is nonrandom, heavily structured and correlated with
environmental variation and stress.
• The study of human genetic diversity has evolutionary significance and
medical applications. It can help scientists understand ancient human
population migrations as well as how human groups are biologically related
to one another.
• For medicine, study of human genetic variation may be important because
some disease-causing alleles occur more often in people from specific
geographic regions.
• The greatest diversity of genetic markers is in Africa indicating it was
the earliest home of modern humans.

4. Causes of genetic diversity in humans
• Genetic variation among humans occurs on many scales, from gross
alterations in the human karyotype (Aneuploidy, Chromosome
abnormalities are detected in 1 of 160 live human births) to
single nucleotide changes.
• There are the factors which cause genetic variation in a population;
1. Single nucleotide polymorphism (SNP).
2. Retrotransposons.
3. Copy number variation (CNV).
4. Insertions or deletions in the genetic sequence.

5. Single neuclotide polymorphisms (SNPs)
• These variations occur at a rate of one in every 100–
300 nucleotides in the human genome.
• In fact, roughly 90 percent of the genetic variation that
exists between humans is the result of SNPs.
• A single base mutation in the APOE (apolipoprotein
E) gene is associated with a lower risk for Alzheimer's
disease.
• More than 335 million SNPs have been found across
humans from multiple populations.
• Genome wide association studies (GWAS) can
determine whether a SNP is associated with a disease
or trait.
Image courtesy- GOOGLE IMAGES

6. Retrotransposons
• Transposon also known as “jumping genes”,
These are discrete pieces of DNA that can move
from site to site within genomes. Transposons
can trigger genomic deletions in humans, as
these deletions can cause several
genetic disorders.
• Non-LTR retrotransposons elements are now
known to affect the human genome in many
different ways generating insertion mutations,
genomic instability, alterations in gene
expression and also contributing to genetic
innovation.
• Examples of Non-LTR retrotransposons are
Alu elements & SVA elements.
IMAGE COURTESY-GOOGLE IMAGES

7. Copy Number Variation (CNV)
• In humans, copy number variations play an important role
in generating necessary variation in the population as well
as disease phenotype.
• Approximately two-thirds of the entire human genome may
be composed of repeats and 4.8–9.5% of the human
genome can be classified as copy number variations.
• One of the most well-known examples of a short copy
number variation(CNV) is the trinucleotide repeat of the
CAG base pairs in the huntingtin gene responsible for the
neurological disorder Huntington's disease.
Image courtesy- Google images

8. 1000 Genomes Project
• launched in January 2008 and to establish by far the most detailed
catalogue of human genetic variation.
• by sequencing 2600 individuals from 26 populations from around the
world.
• To understand how processes like the structural variations like
insertions/deletions, copy number variations (CNV), retroelements, single-
nucleotide polymorphisms (SNPs), and natural selection have shaped the
human genetic diversity.
• The 1000 Genomes Project was aimed to identify 95% of variants that
reside in currently accessible genomic regions and are present at greater
than or equal to 1%.
• This study shows that typical human genome differs at 4.1 million to 5.0
million sites affecting 20 million bases of sequence. that corresponds to
0.6% of total number of base pairs. Nearly all (>99.9%) of these sites are
small differences, either single nucleotide polymorphisms or brief
insertions or deletions (indels) in the genetic sequence.

9. How can we measure genetic differences
among us?
• Wright's Fixation index as measure of variation.
• The population geneticist Sewall Wright developed the fixation
index (often abbreviated to FST) as a way of measuring genetic
differences between populations.
• The fixation index is FST = (HT – HS)/HT ,in which HT and
HS represent heterozygosity of the total population and of
the subpopulation, respectively.
• values >0.25 represent very great genetic variation and that an FST of
0.15–0.25 represented great variation.
• fixation index for humans is about 0.15.
• value of FST can theoretically range from 0.0 (no differentiation) to 1.0
(complete differentiation).

10. Origin of major human groups
• Human evolution started in 7 millions years ago
when human genealogy separated from
chimpanzee and over 20 hominins
were originated.
• Humans originated in Africa and then spread to
other continents.
• Different studies conducted on Y-chromosome
and mitochondrial DNA yielded result that
modern human arose around 100,000-200,000
years ago.
Australopithecus

11. Australopithecus afarensis
• Lived around 3 to 4 million years ago
• This organism, known as Australopithecus afarensis,
probably stood 1 to 1.5 m tall and walked upright, at least
for short distances. But was not an exclusively bipedal.
• Australopithecus afarensis, stood at 1 to 1.5 m tall
• 440cc cranial capacity.
• They were capable of gripping sticks and stones firmly for
vigorous pounding and throwing
IMAGE COURTESY- GOOGLE IMAGES

12. Homo habilis
• The first organisms to be classified in the same genus as Homo
sapiens appeared.
• Existed 1.6 to 2.5 million years ago. This specie have been
named, Homo habilis.
• Height was around 4 ft 10 in And mode of locomotion was
bipedal and has humanlike legs and have been effective long-
distance Travellers.
• Cranial capacity was around 640cc.
• Omnivorous diet.
• Compared to Australopithecus, the opening for the spinal cord is
closer to the middle of the skull, and the skull is reduced in
length and increased in width all hominin characteristics.
Image courtesy- google images

13. Homo erectus
• Existed around 1.8 million years ago
• Also called the upright human.
• Bipedalism.
• average endocranial (brain) capacity of less than 1,000
cubic cm
• First to use fire at around 500,000 years ago.
• First Hominid to leave Africa for Asia and Europe.
• They first hominid to have lived in a monogamous society.
Image courtesy- Google images

14. Homo neanderthalensis
• The braincases of Neanderthal men and women averaged about 1,600 cm3 (98 cu in) and
1,300 cm3 (79 cu in) respectively.
• Average Neanderthal men stood around 165 cm (5 ft 5 in) and women 153 cm (5 ft) tall.
• Cro-Magnon man replaced neanderthal men and Neanderthals went extinct about 40,000
years ago.
• Make use of medicinal plants as well as treat severe injuries, store food, and use
various cooking techniques such as roasting, boiling, and smoking. Neanderthals were
likely capable of speech.
• The 2010 Neanderthal genome project's draft report presented evidence for interbreeding
between Neanderthals and modern humans( Cro-Magnon man).
• While examining mitochondrial DNA, Revealed that it differed from that of modern
humans by 385 bases (nucleotides) in the mitochondrial DNA strand out of approximately
16,500 bases.
• In contrast, the difference between chimpanzees and modern humans is approximately
1,462 mitochondrial DNA base pairs.
• Based on the analysis of mitochondrial DNA, the split of the Neanderthal
and H. sapiens lineages is estimated to date to between 760,000 and 550,000 years ago.

15. IMAGE COURTESY- GOOGLE

16. Image courtesy- google images

17. References;
• Principles of genetics by Snustad & Simmons.
• Auton A, Brooks LD, Durbin RM, Garrison EP, Kang HM, Korbel JO, et al. (October
2015). "A global reference for human genetic variation". Nature. 526 (7571): 68–
74.
• Lewontin RC (1972). "The Apportionment of Human Diversity". Evolutionary
Biology. 6. pp. 381–97.
• "First Diploid Human Genome Sequence Shows We're Surprisingly
Different". Science Daily. 4 September 2007.
• Bourque G, Burns KH, Gehring M, Gorbunova V, Seluanov A, Hammell M, et al.
(November 2018). "Ten things you should know about transposable
elements". Genome Biology. 19 (1): 199.
• Redon R, Ishikawa S, Fitch KR, Feuk L, Perry GH, Andrews TD, et al. (November
2006). "Global variation in copy number in the human
genome". Nature. 444 (7118): 444–54.

18. References;
• Hawks J (2013). Significance of Neandertal and Denisovan Genomes
in Human Evolution. Annual Review of Anthropology. 42. Annual
Reviews. pp. 433–49.
• Keita SO, Kittles RA, Royal CD, Bonney GE, Furbert-Harris P, Dunston
GM, Rotimi CN (November 2004). "Conceptualizing human
variation". Nature Genetics. 36 (11 Suppl): S17–20.