mendal's genetics

1. Mendel’s Genetics
Course: B.Tech Biotech
Subject: Basic of Life Science
Unit: IV

2. Mendel’s Work
• Mendel experimented with thousands of Pea plants
looking at their different traits to understand the
process of heredity. His discoveries form the
foundation of genetics.
• Heredity –the passing of physical
characteristics from parents to
offspring
• Trait- each different form of a characteristic
• Genetics – the study of heredity
1.

3. Mendel’s experiments
2.

4. Mendel’s laws of Inheritance
• Gregor Mendel : conducted hybridisation experiments on garden peas
for seven years (1856-1863) and proposed the laws of inheritance in
living organisms.
• Mendel investigated characters in the garden pea plant that were
manifested as two opposite traits, e.g., tall or dwarf plants, yellow or
green seeds.
• This allowed him to set up a basic framework of rules governing
inheritance, which was expanded on by later scientists to account for
all the diverse natural observations and the complexity inherent in them.

5. • Mendel : artificial pollination/cross pollination experiments using
several true-breeding pea lines.
• A truebreeding line is one that, having undergone continuous self-
pollination, shows the stable trait inheritance and expression for
several generations.
• Mendel selected 14 true-breeding pea plant varieties, as pairs which
were similar except for one character with contrasting traits.
• Some of the contrasting traits selected were smooth or wrinkled seeds,
yellow or green seeds, smooth or inflated pods, green or yellow pods
and tall or dwarf plants

7. Mendel’s Experiments
 Flowering Plant anatomy
 Pistil – produces the female
sex cells or eggs
 Stamens – produce pollen which contains the
male sex cells or sperm
 Fertilization is when the egg and sperm join
forming a new organism
 In plants the pollen must reach the pistil
for fertilization to occur. This is called pollination
3.

8. Pollination
• Pea plants usually self-
pollinate. The pollen from
their stamens lands of the
same plants pistils.
• Mendel developed a
method to cross-pollinate
pea plants. He took pollen
from one pea plant and brushed it
onto the pistil of another.
4.

9. Crossing Pea Plants
• Mendel crossed plants
with contrasting traits
• Ex. Tall plants with short
plants
• Started with pure bred plants –
a purebred organism is
one who is the offspring of
many generations of that have
the same trait
5.

10. The F1 Offspring
• Mendel crossed purebred tall with purebred
short Parental (P) generation
• Tall x short
• Offspring from the cross are called F1 (filial)
• All F1 offspring were tall
6.

11. 7.

12. 8.

13. F2 offspring
• When F1 were full
grown, Mendel
allowed them to self-
pollinate
• F2 were a mix of tall
and short
• ¾ were tall and ¼ were
short
9.

14. Experiments with OtherTraits
• Mendel crossed pea plants with other contrasting traits such
as seed shape, seed color, seed coat color, etc.
• In all crosses the F1 generation had only 1 form of the trait
• In the F2 generation the “lost” form reappeared in ¼ of the
plants.
10.

15. Dominant and Recessive Alleles
• Mendel’s Conclusion
• factors control the inheritance
of traits in peas.
• They exist in pairs
• The female parent contributes
one factor and the male parent
contributes the other factor
• One factor in a pair can mask
or hide the other factor
11.

17. Law of segregation

18. 12.

19. Inheritance of two gene:
• Crossed pea plants that differed in two characters, as is
seen in the cross between a pea plant that has seeds
with yellow color and round shape and one that had seeds
of green color and wrinkled shape.
• Mendel found that the seeds resulting from the crossing of
the parents, had yellow colored and round shaped seeds.

20. Inheritance of two gene:
13.

21. 14.

23. Law of Independent Assortment
• In the dihybrid cross, the phenotypes round,
yellow; wrinkled, yellow; round, green and wrinkled,
green appeared in the ratio 9:3:3:1.
• Such a ratio was observed for several pairs of
characters that Mendel studied.
• The ratio of 9:3:3:1 can be derived as a combination
series of 3 yellow: 1 green, with 3 round : 1 wrinkled.
• This derivation can be written as:
• (3 Round : 1 Wrinkled) (3 Yellow : 1 Green) = 9 Round,
Yellow : 3 Wrinkled, Yellow: 3 Round, Green : 1
Wrinkled, Green

24.  each gamete having either R or r, it should also have the allele
Y or y.
 The important thing to remember here is that segregation of 50
per cent R and 50 per cent r is independent from the
segregation of 50 per cent Y and 50 per cent y.
 50 per cent of the r bearing gamete has Y and the other 50
per cent has y.
 Similarly, 50 per cent of the R bearing gamete has Y and the
other 50 per cent has y.
 Thus there are four genotypes of gametes (four types of pollen
and four types of eggs).
 The four types are RY, Ry, rY and ry each with a frequency
of 25 percent or ¼th of the total gametes produced.

25. Sex determination
Henking (1891) could identified a specific nuclear structure
throughout spermatogenesis in a few insects
Observation: 50 per cent of the sperm received this structure
after spermatogenesis, whereas the other 50 per cent sperm did
not receive it.
this structure - X body ,
but he could not explain its significance.
investigations by other scientists : ‘X body’
X body : chromosome X-chromosome.
large number of insects the mechanism of sex determination: XO type,
i.e., all eggs bear an additional X-chromosome besides the other
chromosomes (autosomes).

26. • some of the sperms : X-chromosome whereas some do not.
• Eggs fertilised by sperm having an X-chromosome
become females and, those fertilised by sperms that do
not have an X-chromosome become males.
• Among the males an X-chromosome is present but its
counter part is distinctly smaller and called the
Y-chromosome.
• the males have autosomes plus XY, while female have
autosomes plus XX.

27. • The sex of a child will be determined by types of sperm.
• As the numbers of X bearing sperm is equal to the numbers
of Y bearing sperm, the chance of having baby boy and
baby girl for each birth is 50%.
• Ratios of males to females is 1:1

28. Both in humans and
in Drosophila, the female has a
pair of
XX chromosomes
(homogametic) and the
male XY (heterogametic)
composition;
15.

29. 16.

30. Mutation
• Mutation : alteration of DNA sequences.
• changes in the genotype and the phenotype of
an organism.
• In addition to recombination, mutation is
another phenomenon that leads to variation in DNA.
• one DNA helix runs continuously from one end to
the other in each chromatid, in a highly
supercoiled form.

31. • Loss or gain of a segment of DNA : alteration
in chromosomes.
• Since genes are known to be located
on chromosomes, alteration in chromosomes
results in abnormalities or aberrations.
• Chromosomal aberrations : cancer cells.

32. Types of Mutation
1.Point Mutation : change in a single base pair
of DNA.
• E.g., sickle cell anemia
2. Frame shift Mutation : Deletions and insertions
of base pairs of DNA.
3. Mutagen :chemical and physical factors that
induce mutations.
• UV radiations can cause mutations in organisms –
it is a mutagen.

33. Genetic disorder
• 1. Pedigree Analysis:
• In the pedigree analysis the inheritance of a particular trait is
represented in the family tree over generations.
• In human genetics, pedigree study provides a strong tool, which
is utilized to trace the inheritance of a specific trait,
abnormality or disease.
• Some of the important standard symbols used in the pedigree
analysis.
• A number of disorders in human beings have been found to be
associated with the inheritance of changed or altered genes or
chromosomes.

34. 17.

35. • 2. Mendelian Disorder:
• mutations in single genes.
• Transmitted to offspring.
• Mendelian disorders can be traced in a family by
the pedigree analysis.
• Examples: Hemophilia, Cystic fibrosis, Sickle-cell
anaemia, Color blindness, Phenylketonuria,
Thalesemia, etc.

36. Hemophilia, the royal disease
• Hemophilia is the oldest
known hereditary bleeding
disorder.
• Caused by a recessive gene
on the X chromosome.
• There are about 20,000
hemophilia patients in the
United States.
• One can bleed to death with
small cuts.
• The severity of hemophilia
is related to the amount of
the clotting factor in the
blood. About 70% of
hemophilia patients have
less than one percent of the
normal amount and, thus,
have severe hemophilia.

37. • Hemophilia is a group of hereditary genetic disorders that impair the
body's ability to control blood clotting or coagulation, which is used to
stop bleeding when a blood vessel is broken.
• Haemophilia A (clotting factor VIII deficiency) is the most common
form of the disorder, present in about 1 in 5,000–10,000 male births.
• Haemophilia B (factor IX deficiency) occurs in around 1 in about
20,000–34,000 male births.
• Like most recessive sex-linked, X chromosome disorders, haemophilia
is more likely to occur in males than females. This is because females
have two X chromosomes while males have only one, so the defective
gene is guaranteed to manifest in any male who carries it. Because
females have two X chromosomes and haemophilia is rare, the
chance of a female having two defective copies of the gene is very
remote, so females are almost exclusively asymptomatic carriers of
the disorder.
• Female carriers can inherit the defective gene from either their
mother or father, or it may be a new mutation.

38. • Haemophilia lowers blood plasma clotting factor levels of the
coagulation factors needed for a normal clotting process.
• Thus when a blood vessel is injured, a temporary scab does form,
but the missing coagulation factors prevent fibrin formation, which
is necessary to maintain the blood clot.
• A haemophiliac does not bleed more intensely than a person
without it, but can bleed for a much longer time.
• In severe haemophiliacs even a minor injury can result in blood loss
lasting days or weeks, or even never healing completely.
• In areas such as the brain or inside joints, this can be fatal or
permanently debilitating.

39. Phenylketonuria or PKU
People with PKU cannot consume any product that
contains aspartame.
PKU is a metabolic disorder that results when the PKU
gene is inherited from both parents
Caused by a deficiency of an enzyme which is necessary
for proper metabolism of an amino acid called
phenylalanine.

40. PKU
• Phenylalanine is an essential amino acid
and is found in nearly all foods which
contain protein, dairy products, nuts,
beans, tofu… etc.
• A low protein diet must be followed.
• Brain damage can result if the diet is not
followed causing mental retardation…and
mousey body odor.

41. • Phenylketonuria (PKU) is an autosomal recessive metabolic
genetic disorder characterized by homozygous or compound
heterozygous mutations in the gene for the hepatic enzyme
phenylalanine hydroxylase (PAH), rendering it nonfunctional.
This enzyme is necessary to metabolize the amino acid
phenylalanine (Phe) to the amino acid tyrosine (Tyr).
• When PAH activity is reduced, phenylalanine accumulates and is
converted into phenylpyruvate (also known as phenylketone),
which can be detected in the urine.
• Untreated PKU can lead to intellectual disability, and other
serious medical problems. The mainstream treatment for
classic PKU patients is a strict PHE-restricted diet supplemented
by a medical formula containing amino acids and other
nutrients. In the United States, the current recommendation is
that the PKU diet should be maintained for life.

42. PKU

43. Sickle Cell Anemia
• An inherited, chronic
disease in which the red
blood cells, normally
disc-shaped, become
crescent shaped. As a
result, they function
abnormally and cause
small blood clots. These
clots give rise to
recurrent painful
episodes called "sickle
cell pain crises".
18.

44. Sickle Cell
• Sickle cell disease is most commonly found
in African American populations. This
disease was discovered over 80 years ago,
but has not been given the attention it
deserves.

45. • 3. Chromosomal disorders
• caused due to absence or excess or abnormal arrangement of one
or more chromosomes.
• Failure of segregation of chromatid during cell division cycle results
in the gain or loss of a chromosome(s), called aneuploidy.
For example,
• Down’s syndrome results in the gain of extra copy of chromosome
21.

46. • Failure of cytokinesis after telophase stage of
cell division results in an increase in a whole
set of chromosomes in an organism and, this
phenomenon is known as polyploidy.

47. Down’s Syndrome
• Caused by non-
disjunction of the
21st chromosome.
• This means that the
individual has a
trisomy (3 – 2lst
chromosomes).

48. • Down syndrome (DS) or Down's syndrome, also
known as trisomy 21, is a genetic disorder caused by
the presence of all or part of a third copy of
chromosome 21. It is typically associated with
physical growth delays, characteristic facial features,
and mild to moderate intellectual disability.
• Down syndrome is the most common chromosome
abnormality in humans, occurring in about one per
1000 babies born each year.

49. Down’s Syndrome
or Trisomy 21
19.

50. Symptoms of Down Syndrome
• Upward slant to eyes.
• Small, flattened nose.
• Small mouth, making tongue appear large.
• Short neck.
• Small hands with short fingers.
• Low muscle tone.
• Small skin folds at the inner corners of the eyes.
• Excessive space between first and second toe and
• Mental retardation

51. Kleinfelter’s syndrome
(or Klinefleter’s)
• Disorder occurring due to nondisjunction of
the X chromosome.
• The Sperm containing both X and Y combines
with an egg containing the X, results in a male
child.
• The egg may contribute the extra X
chromosome.

52. XXY
• Males with some development of breast tissue
normally seen in females.
• Little body hair is present, and such person are
typically tall, have small testes.
• Infertility results from absent sperm.
• Evidence of mental retardation may or may not
be present.

53. Web and Books References
• Book name : 12th std NCERT
• Book name : Genome by T.A.Brown
• http://www.ndsu.edu/pubweb/~mcclean/plsc431/mutation/
mutation4.htm
• http://en.wikipedia.org/wiki/Mutation
• http://en.wikipedia.org/wiki/Mendelian_inheritance
• http://www.hobart.k12.in.us/jkousen/Biology/mendel.htm
Management 8/e - Chapter 8 53

54. Image References
• 1.http://www.artexpertswebsite.com/portraitid/scientists/scientists_images/
mendel2.jpg
• 2.http://nitro.biosci.arizona.edu/courses/EEB195/Lecture02/pics/pea.jpeg
• 3.http://kmbiology.weebly.com/uploads/6/0/1/1/6011704/198367.jpg?364
• 4.http://kmbiology.weebly.com/uploads/6/0/1/1/6011704/198367.jpg?364
• 5.http://www.exploringnature.org/graphics/anatomy/pea_traits2.jpg
• 6.http://wallpapersfun.files.wordpress.com/2011/07/gregormendelpeas12.jpg
• 7. https://abagond.files.wordpress.com/2011/07/mendel.gif
• 8.http://cbse.meritnation.com/img/study_content/lp/1/10/10/153/375/899/
190/21.05.08-shivangi-biology-10.2.9.1.2_SG_html_mdb3db29.png
• 9. http://www.thisoldearth.net/Images/Mendal_peas.jpg
• 10.http://wallpapersfun.files.wordpress.com/2011/07/gregormendelpeas12.jp
g

55. • 11. https://online.science.psu.edu/sites/default/files/biol011/Fig-6-2-F2-
Generation.jpg
• 12. http://www.prism.gatech.edu/~gh19/b1510/segregat.gif
• 13.http://biotechlearn.org.nz/var/biotechlearn/storage/images/themes/
mendel_and_inheritance/images/inheritance_of_multiple_traits_in_peas
/457375-1-eng-AU/inheritance_of_multiple_traits_in_peas_oversize.jpg
• 14.http://activity.ntsec.gov.tw/lifeworld/english/content/images/en_gene
_c4d.jpg
• 15. & 16. & 17. 12th NCERT Book
• 18.http://thumb1.shutterstock.com/display_pic_with_logo/1584560/1352
45900/stock-photo-red-blood-cells-blood-elements-red-blood-cells-
responsible-for-oxygen-carrying-over-regulation-135245900.jpg
• 19.http://592f46.medialib.glogster.com/media/d868c55770ddebb16f361e
00d66bf4cadca273f7672eb2e7c745a44ca3c2010e/trisomy.jpg

56. Thank You