Heredity involves the transmission of genetic information from parents to offspring. Genetics is the study of heredity. Mitosis and meiosis are the two types of cell division involved in heredity. Mitosis produces genetically identical cells for growth and tissue repair, while meiosis produces haploid gametes through two divisions resulting in four genetically distinct cells. Meiosis ensures genetic diversity and integrity in sexually reproducing organisms.
1. Heredity
Inheritance (transmission) of certain characteristics from one generation
to the following one
* GENETICS is the branch of Biology that studies heredity
* ZYGOTE one cell that contains ALL the inherited genetic information
Heredity
Mitosis Meiosis
* nuclear division which produces
* produces haploid gametes that
from 1 cell, 2 genetically
are genetically different.
identical, diploid cells
* only in reproductive organs
* Produced in all the growing
tissues (somatic cells)
2.
3. Role of Mitosis
1) Faithful copying of
genes and their transfer to
the next generation of
nuclei or cells
2) Maintains the correct
chromosome number of
somatic cells.
3) Formation of a
multicellular organism
4) Cell replacement and
regeneration
5. Stages of mitosis
Chromosomes appear, nucleus
interphase disappears
M prophase Chromatids pulled to poles
I
T metaphase Chromosomes invisible; DNA
O replicates
S anaphase Cytoplasmic division
I
S
telophase Chromosomes at equator, spindle
forms
cytokinesis
Chromatids at poles, nucleus
reforms
6. Prophase
The Cell begins
the division
process
1. The nucleolus
disappears,
2. The nuclear
membrane
breaks apart
7. 3. The chromosomes
become visible
4. The spindle
apparatus forms
and attaches to
the centromeres
of the
chromosomes
8. Metaphase
The Second Phase
of Mitosis
1. The Nuclear
Membrane is
completely gone
2. The duplicated
chromosomes line
up along the cell's
equator.
9.
10. Anaphase
The third phase of
Mitosis
Diploid sets of daughter
chromosomes separate
They are pushed and
pulled toward opposite
poles of the cell by the
spindle fibers
14. Cytokinesis – The final stage of Mitosis
The cytoplasm, organelles, and nuclear
material are evenly split and two new
cells are formed.
Cell
Plate
15. Chromosome
A threadlike structure within the cell that carries the
genetic material as a linear strand of DNA bonded to
various proteins (gene) in the nucleus of eukaryotic
cells.
The chromosomes are always in pairs because
one of them is derived from the male parent and
the other from the female parent
Different species have different numbers
and shapes of chromosomes
Members of the same species have
identical sets of chromosomes
16. Genes * are the chemical component of the chromosomes
•Control the development of a particular characteristic in a
living organisms
• provide the ”instructions”
•Genes are in pairs so the genes they carry are also in pairs
Genes controlling the same characteristics occupy identical
positions on corresponding chromosomes
Each member of a pair of genes comes
A a
from either the male or the female
B b parent just as the chromosomes do
C c
D d The individual genes of a pair, control
E e the same characteristic (ALLELES), e.g. B
F f and b
could control eye colour; G and g could
G g control hair colour (they only carry out
H h their function in the correct situation)
I I The gene is EXPRESSED
17. Why do we need meiosis?
It is the fundamental basis of sex.
What is the purpose of sex?
- to bring two haploid
gametes together to
form a diploid zygote.
n (mom) + n (dad)
= 2n (offspring)
18. Meiosis
ensures that
all living
organisms
will maintain
both Genetic
Diversity and
Genetic
Integrity
19. Why form gametes?
• Goal: Reduce genetic material by half
from mom from dad child
too
much!
meiosis reduces
genetic content
20. Meioisis vs. Mitosis
Mitosis Meiosis
Number of 2
1
divisions
Number of
2 4
daughter cells
Genetically
Yes No
identical?
Chromosome # Same as parent Half of parent
Where Somatic cells Germline cells
When Throughout life At sexual maturity
Growth and Sexual
Role
repair reproduction
21. • Start with 46 double
stranded
chromosomes (2n)
– After 1st division - 23
double stranded
chromosomes (n)
– After 2nd division - 23
single stranded
chromosomes (n)
• Occurs in our germ
cells
– cells that produce our
gametes
– egg and sperm
22. A form of cell division happening in sexually reproducing
organisms by which two consecutive nuclear divisions occur
without the chromosomal replication in between, leading to the
production of four haploid gametes (sex cells)
Meiosis 1 Meiosis 2
23. During Meiosis gamete (sex) cells undergo a
“double division”, maintaining the DNA, but
reducing the chromosomal count to 23
+ =
Sperm (23) + Egg (23) = Fertilized Cell (46)
25. Gene Structure Formed by DNA
Group of molecules
A DOUBLE chain of NUCLEOTIDS
in the form of a helix
Phosphate
5-carbon
group Organic
sugar molecule
base
Joins the nucleotids
to form a long chain Adenine
Thymine
Cytosine
Guanine
26. A+T
C+G
HELICASE unwinds the 2 strands of DNA
Other enzymes bring nucleotides to join them to the unzipped DNA
The new nucleotides join up to form a chain attached to the exposed
strand the double helix is REPLICATED
28. MUTATION
Any spontaneous change in the DNA sequence
(in a gene or a chromosome) of an organism
1 or more are •Damage or loss of a
During mitosis or
not replicated correctly part
meiosis
• gain of extra
chromosome or part
– a mutation that occurs
in many genes and
affects many traits at
Eye color, Sickle cell
once.
Anemia, Hemophilia
Ex: Down Syndrome
(an extra 21st
chromosome)
29. * Body cell mutations (during MITOSIS) can cause
cancer. only the individual is affected.
* Gamete cell mutations (during MEIOSIS) affect the
egg and the sperm. all offspring of the individual
can be affected.
30. MUTATION
It results in a defective enzyme disrupts the
reactions in the cell
• Most are neutral
• Some are harmful
• Some are beneficial
– Polyploidy plants are larger and stronger
– Mutations lead to evolution in living organisms
Origin/Cause of Mutation
• Spontaneous: due to errors in the genetic
machinery during DNA replication
• Induced: arising from exposure to mutagenic
agents (tobacco/X-rays/Ultraviolet radiation)
31. Only 3% of DNA consists
of GENES
The rest is a repeated sequences of
nucleotides that don’t code for proteins
If mutations occur there, they are unlikely to
have any effect on the organism
Neutral mutation
32. Example of Genetic
disorder
1) Down syndrome
• 47, trisomic 21
CHROMOSOME
MUTATION
• During MEIOSIS one
of the chromosomes
fails to separate from
the homologous
partners
Ovum carries 24 chromosomes
Turner syndrome (TS) is a medical disorder that affects about 1 in every 2,500 girls. Although researchers don't know exactly what causes Turner syndrome, they do know that it's the result of a problem with a girl's chromosomes . Girls with Turner syndrome are usually short in height. Those who aren't treated for short stature reach an average height of about 4 feet 7 inches (1.4 meters). The good news is that when Turner syndrome is diagnosed while a girl is still growing, she can be treated with growth hormones to help her grow taller. http://kidshealth.org/teen/diseases_conditions/sexual_health/turner.html Most girls are born with two X chromosomes, but girls with Turner syndrome are born with only one X chromosome or they are missing part of one X chromosome. The effects vary widely among girls with Turner syndrome. It all depends on how many of the body's cells are affected by the changes to the X chromosome. In addition to growth problems, Turner syndrome prevents the ovaries from developing properly, which affects a girl's sexual development and the ability to have children. Because the ovaries are responsible for making the hormones that control breast growth and menstruation, most girls with Turner syndrome will not go through all of the changes associated with puberty unless they get treatment for the condition. Nearly all girls with Turner syndrome will be infertile, or unable to become pregnant on their own.
Klinefelter's syndrome, 47, XXY, or XXY syndrome is a condition in which human males have an extra X chromosome. While females have an XX chromosomal makeup, and males an XY, affected individuals have at least two X chromosomes and at least one Y chromosome. [1] Because of the extra chromosome, individuals with the condition are usually referred to as "XXY Males", or "47, XXY Males". [2] This chromosome constitution (karyotype) exists in roughly between 1:500 to 1:1000 live male births [3][4] but many of these people may not show symptoms. The physical traits of the syndrome become more apparent after the onset of puberty, if at all. [5] In humans, 47XXY is the most common sex chromosome aneuploidy in males [6] and the second most common condition caused by the presence of extra chromosomes. Other mammals also have the XXY syndrome, including mice. [7] Principal effects include hypogonadism and reduced fertility. A variety of other physical and behavioural differences and problems are common, though severity varies and many XXY boys have few detectable symptoms. Not all XXY boys and men develop the symptoms of Klinefelter syndrome.