Download Early Beliefs and Mendel

From Mendel to DNA
Recap from previous lessons
1. Mitosis produces daughter cells with:
a. fewer chromosomes than the parent cell
b. more chromosomes than the parent cell
c. the same number of chromosomes as the
parent cell
-C
2. As a result of mitosis, how many cells
are produced?
a. One
b. Two
c. Four
-B
3. How many pairs of chromosomes
does a human body cell contain?
a. 4
b. 23
c. 46
-B
4. Which statement about sex
chromosomes is correct?
a. Females are XY and males are XX.
b. Females and males are XX.
c. Females are XX and males are XY.
-C
5. Where are the cell's chromosomes
found?
a. In its nucleus.
b. In its cytoplasm.
c. In its mitochondria.
-A
6. Compared to a body cell, a gamete
contains:
a. Half the genetic information.
b. The same amount of genetic information.
c. Twice the genetic information.
-A
Higher Questions
7. During meiosis:
a. No copies of the chromosomes are made.
b. Gametes are formed, each with a single set
of chromosomes.
c. The cell divides five times to form four
gametes.
-B
8. As a result of meiosis, how many sex
cells are produced?
a. One
b. Two
c. Four
-C
Learning Objectives
1. To understand the work Mendel carried
out and why its importance was not
recognised until after his death.
2. To know why DNA fingerprinting is
possible.
Pioneer of Genetics:
Gregor Mendel
4
One of the classic scientific experiments on inheritance was
performed by an Austrian monk named Gregor Mendel
(1822–1884)
Mendel’s work with garden peas…..
Why did Mendel choose the garden pea on which to
perform his work?
Chromosomes
o The 2 chromosomes in each pair
carry information for the same
characteristic
o Examples of characteristic
include eye colour, hair colour
etc...
o So each body cell has 2 sets of
information for all of your
characteristics
One set of
information
for eye
colour from
mother
One set of
information
for eye
colour from
father
o One set is inherited from your
mother the other from your
father
Inheritance of Characteristics
o Just like us, the pea plants
chromosomes also come in pairs
o And just like us, each pair carries
genes for the same characteristic
o Sometimes the form of these genes
are different and sometimes they
are the same
One set of
information
from ‘mother’
o Different forms of genes are
called alleles
One set of
information
from ‘father’
Inheritance of Characteristics
White and
Purple pea
plant bred
together
All the offspring (F1 generation) are Purple
Inheritance of Characteristics
2 purple
pea plants
from the
F1
generation
crossed
The offspring (F2 generation) are purple and white.
Mendel wondered how white flowers could disappear for a
generation but then come back
Inheritance of Characteristics
o The combination of alleles determines
what our characteristics will be
o Alleles can be either Dominant or
Recessive
o You will always see the effect of the
dominant allele over the recessive one.
Allele Example
o In pea plants Purple flowers are dominant
and white flowers are recessive
For a flower to be white
it must have 2 white
alleles. Since the white
colour is recessive
For a flower to be purple it
could have 2 purple alleles
or one white and one purple
allele. Since purple is the
dominate colour
We can show inheritance of flower colour using a genetic
diagram. We use capital letters to represent the dominant
allele and the same lower case letter to represent the
recessive allele.
PP
pp
Pp
Pp
Pp
P
p
P
PP
Pp
p
Pp
pp
Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel,
Mendel
1.
When a tall pea plant was crossed with a dwarf pea plant – all
offspring were tall pea plants (i.e. 100% identical)
2.
When the two offspring (tall pea plants), three of the
offspring were tall and one was a dwarf (i.e. 3:1)– why?
Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel,
Genetic Crosses
Tall x Dwarf
TALL plants (TT)
DWARF
plants
(tt)
100 ‘Tt’
T
T
t
Tt
Tt
t
Tt
Tt
As ‘T’ is DOMINANT and
‘t’ is RECESSIVE,
All plants are TALL
carriers.
Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel,
Genetic Crosses
Tall Carrier x Tall Carrier
TALL CARRIER plants (Tt)
TT = Tall
T
t
Tt = Tall
T
TT
Tt
tt = dwarf
t
Tt
tt
So 3:1
Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel,
Genetic Crosses
Alleles are different forms of the same gene.
Normal Boring Hamster
Wild
Scatty
Hamster
B
B
b
Bb
Bb
b
Bb
Bb
All Bb
So, all are normal
and boring hamsters.
Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel,
Genetic Crosses
Bb x Bb – What are their offspring like?
BB = boring
B
b
Bb =boring
B
BB
Bb
bb = wild
b
Bb
bb
So 3:1
Recessive
• He published a
book of his findings
in 1866, when he
was 44 years old.
• People did not
understand his
theories as no one
had seen
chromosomes.
• He died 20 years
later with no one
taking notice of his
work.
• 16 years after his death people could
finally see chromosomes through a
microscope and he was given the
recognition for his findings.
Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel,
Cystic Fibrosis
This is a genetic disorder of the
cell membranes. It results in a
thick sticky mucus in the air
passages and in the pancreas.
Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel,
Huntington’s
This is a genetic disorder of the
nervous system which results in
shaking, erratic body movements
and eventually severe mental
deterioration.
Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel,
Genetic Disorders
1.
Cystic Fibrosis is caused by a recessive allele. For a child to have
Cystic Fibrosis, but its parents not to have the condition, what
must the parent genetic code be? Draw a genetic diagram to
explain your answer.
Cc x Cc
2. Huntington’s is a disease that is caused by a dominant allele. What
is the chance of offspring having Huntington’s when one parent is
normal and the other is a carrier/sufferer? 50% (Nn x nn)
3. Before embryos are inserted back into the female in IVF, the
embryo are screened for genetic disorders. Is the screening of
embryo’s right or wrong?
Single-Trait Inheritance
1. Since one allele is inherited from each parent,
various genotypes are possible.
2. The dominant phenotype is expressed if the
offspring is either heterozygous or homozygous for the
dominant allele.
3. The recessive phenotype is expressed only if the
offspring is homozygous for the recessive allele.
4. When there are multiple alleles for a given
characteristic, the alleles have a dominance
hierarchy.