7/29/2019 2. Principles of Inheritance
1/52
Most slide were adapted directly from various sources in the internet
7/29/2019 2. Principles of Inheritance
2/52
Native Hybrid
S
EL
E
C
T
I
V
E
breeding
7/29/2019 2. Principles of Inheritance
3/52
8000-3000 BC. Egyptian domestication of animals
7/29/2019 2. Principles of Inheritance
4/52
How are traits passed on from
parents to children?
The study of how traits are inherited or
how genetic information is passed from
one generation to the next is called
GENETICS
Genetics also explains biological variation
7/29/2019 2. Principles of Inheritance
5/52
1. Pre-Mendelian blending theory
2. Gene theory (which traces back to
Mendel)
How are traits passed on from
parents to children?
7/29/2019 2. Principles of Inheritance
6/52
1. 19th Century Hypothesis(before Mendel)
inheritance was the blending ofcharacteristics
We look somewhat like our parents characteristics were merely added together:
the next generation is a blend
How would the population look like
after many generations?
7/29/2019 2. Principles of Inheritance
7/52
Blending in Parakeet:
Yellow x Green = Blue?
Several shades!!!
7/29/2019 2. Principles of Inheritance
8/52
Fact: There is tremendous diversity of life forms
About 8.8 million species; onlya quarter has been discovered!!!
7/29/2019 2. Principles of Inheritance
9/52
inheritance as the blending ofcharacteristics was incorrect
No one studied theproblem systematicallyuntil Gregor Mendel
(1822-1884)
1. 19th Century Hypothesis(before Mendel)
7/29/2019 2. Principles of Inheritance
10/52
Gregor Mendel (1822-1884)
A little known Austrian monk (flunked out ofcollege twice but became a mathematician)
Spent adult life in relative obscurity doing
basic genetics research and teaching highschool mathematics, physics, and Greek inBrno, Czech Republic
Published his ideas in 1866; work largely wentunrecognized until 1900, which was long afterhis death.
7/29/2019 2. Principles of Inheritance
11/52
Why study Mendel
He was the first to demonstrate the principles
of inheritance
He used a systematic scheme based upon an
understanding of mathematics and statistics
before formal statistics was developed
He applied his knowledge of mathematics
with an excellent scientific method
7/29/2019 2. Principles of Inheritance
12/52
2. Today: The gene theory
An alternative idea to blending is the
gene idea.
Parents pass on discrete individualheritable units called genes
Genes are segments of DNA in a
chromosome A gene has different forms/variations
called alleles
7/29/2019 2. Principles of Inheritance
13/52
7/29/2019 2. Principles of Inheritance
14/52
What is a gene?
A gene is a stretch of DNA whose sequencedetermines the structure and function of a
specific functional molecule (usually a protein)
DNA
Protein
GAATTCTAATCTCCCTCTC
AACCCTACAGTCACCCATTT
GGTATATTAAAGATGTGTTG
TCTACTGTCTAGTATCC
Computer program
Specific function
functionsf(){document.
f.q.focus()}
Working copymRNA
7/29/2019 2. Principles of Inheritance
15/52
Homologous chromosomes bear the two
alleles for each characteristic
Alternative forms of a gene reside at the samelocus on homologous chromosomes
7/29/2019 2. Principles of Inheritance
16/52
DNA
(deoxyribonucleic acid)
mRNA
Protein
7/29/2019 2. Principles of Inheritance
17/52
Karyotyping
is matching
the paired
chromosomes
7/29/2019 2. Principles of Inheritance
18/52
Down syndrome karyotype
(trisomy 21)
7/29/2019 2. Principles of Inheritance
19/52
Mendels experiments
7/29/2019 2. Principles of Inheritance
20/52
Mendels
data
7/29/2019 2. Principles of Inheritance
21/52
Mendel deduced the underlying principles of
genetics from these patterns
1. Segregation
2. Dominance
3. Independent
assortment
7/29/2019 2. Principles of Inheritance
22/52
1. Mendels Law of Segregation
A normal (somatic) cell has two variants (alleles) for aMendelian trait.
A gamete (sperm, egg, pollen, ovule) contains one allele,
randomly chosen from the two somatic alleles.
E.g. if you have one allele forbrown eyes (B) and one for
blue eyes (b), somatic cells
have Bb and each gamete
will carry one of B or b
chosen randomly.
B b
B BB Bb
b Bb bb
Eggs
Sperm
7/29/2019 2. Principles of Inheritance
23/52
Two types of cell division
Mitosis Meiosis
All body cells Sex cells:
egg/sperm
2 daughter cells 4 d-cells
Equal # of
chromosome/s
Half of the number
7/29/2019 2. Principles of Inheritance
24/52
1. Mitosis: by all body cells
Cell cycle:
G Growth
S - Synthesis
M - Mitosis
Homologoue = pair of the same type of chromatids
Diploid = paired state
Haploid = unpaired
7/29/2019 2. Principles of Inheritance
25/52
2. Meiosis: in gametes (sperm or egg) only
Gametes are either egg or spermChiasma point of crossing over (recombination)
7/29/2019 2. Principles of Inheritance
26/52
Meiosis in a Nutshell
Meiosis is a special type of cell division that
occurs in sexually reproducing organisms.
It reduces the chromosome number by half,enabling sexual recombination to occur.
Itensures that an organism has the samenumberof chromosomes in each generation.
7/29/2019 2. Principles of Inheritance
27/52
Terminology
Haploid:
containing one
copy of each
chromosome
(n=23)
B b
B BB Bb
b Bb bbEggs
Sperm
Diploid:
containing two
copies of eachchromosome
(2n=46)
Punnett Square of a Monohybrid Cross
7/29/2019 2. Principles of Inheritance
28/52
Terminology
Genotype: the states of the two alleles at one
or more locus associated with a trait
Phenotype: the state of the observable trait
Genotype Phenotype
BB (homozygous) Brown eyes
Bb (heterozygous) Brown eyes
bb (homozygous) Blue eyes
7/29/2019 2. Principles of Inheritance
29/52
2. Mendels Law of Dominance
If your two alleles are different (heterozygous,e.g. Bb), the trait associated with only one of
these will be visible (dominant) while the
other will be hidden (recessive).E.g. B is dominant
b is recessive
B b
B BB Bb
b Bb bb
Eggs
Sperm
7/29/2019 2. Principles of Inheritance
30/52
2. Law of Dominance...
If your two alleles are different (heterozygous, e.g. Bb),the trait associated with only one of these will be visible
(dominant) while the other will be hidden (recessive).
E.g. B is dominant, b is recessive.
B b
B BB Bb
b Bb bb
Eggs
Sperm
7/29/2019 2. Principles of Inheritance
31/52
3. Mendels Law ofIndependent
Assortment
Knowledge of which allele has been inherited at one
locus gives no information on the allele that has been
inherited at the other locus
S/s Y/y
SY Sy sY sy
25% 25% 25% 25%
7/29/2019 2. Principles of Inheritance
32/52
S Y
s y
Gametophytes
(gamete-
producing
cells)
S Y
s yGametes
S y
s YRecombinants
Recombination
Segregation
3. Law ofIndependent Assortment.
Red father
Blue - mother
7/29/2019 2. Principles of Inheritance
33/52
Simplified view of eye colour inheritance: bi-
allelic Mendelian trait
- Brown dominant: BB, Bb
Blue recessive: bb
Human eye colour
B b
B BB Bb
b Bb bbEggs
Sperm
7/29/2019 2. Principles of Inheritance
34/52
Human eye colour
?
B?
B?B?B? bb
bb B?
BB, Bb (Brown, dominant) Bb (blue, recessive)
What are the possible eye color/s of this child?
7/29/2019 2. Principles of Inheritance
35/52
Non-Mendelian Inheritance:
Incomplete Dominance
Some alleles for a
gene are not
completely
dominant over the
others. Thisresults in partially
masked
phenotypes which
are intermediate tothe two extremes.
7/29/2019 2. Principles of Inheritance
36/52
Non-Mendelian : Sex Linkage
All chromosomes are homologous except on
sex chromosomes.
Sex chromosomes are eitherX orY.
If an organism is XX, it is a female, if XY it ismale.
If a recessive allele exists on the X
chromosome. It will not have a corresponding
allele on the Y chromosome, and will therefore
always be expressed
7/29/2019 2. Principles of Inheritance
37/52
The 23rd pair of chromosome during
fertilization
Possible
combinations
Sex: F F M M 1 female: 1 male
7/29/2019 2. Principles of Inheritance
38/52
Human Sex Linkage
Hemophilia (X-linked): Disorder of the blood
where clotting does notoccur properly due to afaulty protein.
Occurs on the Xchromosome, and isrecessive.
Thus a vast majority ofthose affected are males.
First known person knownto carry the disorder was
Queen Victoria of England.Thus all those affected arerelated to Europeanroyalty.
P f di i h i k f 1000 f
7/29/2019 2. Principles of Inheritance
39/52
Patterns of disease inheritance known for 1000s of
years, e.g. haemophilia
7/29/2019 2. Principles of Inheritance
40/52
Colour blindness is usually passed down from
mother to son on the 23rd chromosome (X-linked)
7/29/2019 2. Principles of Inheritance
41/52
7/29/2019 2. Principles of Inheritance
42/52
7/29/2019 2. Principles of Inheritance
43/52
Y-linked inheritance
baldness hairy ear lobes
7/29/2019 2. Principles of Inheritance
44/52
Phenotypes are controlled by more than 1 allele. Eg. Blood types
are regulated by 3 separate genes.
ABO Blood typing Humans have multiple types of surface antigens on RBC's
The nature of these surface proteins determines a person'sBlood Type.
There are 3 alleles which determine blood type IA, IB, or IO. Thisis referred to as having multiple alleles
Human blood types are designated as A, B or O. Type A denotes having the A surface antigen, and is denoted by IA
Type B denotes having the B surface antigen, and is denoted by IB
Type O denotes having neither A or B surface antigen, and isdenoted by IO
There are several blood type combinations possibleA , B, AB (Universal recipient) , O (Universal donor)
Non-Mendelian: Multiple Alleles
7/29/2019 2. Principles of Inheritance
45/52
Non-Mendellian: Continuous Variation
Many traits
may have a
wide range of
continuous
values. Eg.Human height
can vary
considerably.
There are notjust "tall" or
"short" humans
7/29/2019 2. Principles of Inheritance
46/52
Non-Mendelian: mtDNA
Mitochondrial DNA point mutations are maternally inherited and can
occur in rRNA or tRNA genes, or in genes coding for proteins of
respiratory chain complexes.
7/29/2019 2. Principles of Inheritance
47/52
Phenotypes associated with mtDNA
mutations
Longevity
Stroke
Seizures Reduced sperm motility
Common migraine
Bipolar disorder Exercise intolerance,
fatigability
7/29/2019 2. Principles of Inheritance
48/52
Non-Mendellian:
Gene interaction: Many biological pathways are governed by multiple
enzymes, involving multiple steps. If any one of thesesteps are altered. The end product of the pathway
may be disrupted.
Environmental effects: Sometimes genes will not be fully expressed owing to
external factors. Example: Human height may not befully expressed if individuals experience poornutrition.
7/29/2019 2. Principles of Inheritance
49/52
Summary
Mendel deduced three simple laws ofinheritance:
Segregation
Dominance Random assortment
The majority of traits dont follow these
rules but Mendels laws are neverthelesscrucial to understanding almost all genetic
inheritance
7/29/2019 2. Principles of Inheritance
50/52
Levels of biological diversity:
Species diversity
Ecosystem diversity
Genetic diversity Molecular diversity
7/29/2019 2. Principles of Inheritance
51/52
Watch
http://highered.mcgraw-
hill.com/sites/0072495855/student_view0/ch
apter2/animation__mitosis_and_cytokinesis.h
tml
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html7/29/2019 2. Principles of Inheritance
52/52
Web sites to check
http://gslc.genetics.utah.edu/units/basics/tour/inheritance.swf
http://science.nhmccd.edu/biol/genetics.html
http://library.thinkquest.org/20465/games.html
http://gslc.genetics.utah.edu/units/basics/tour/inheritance.swfhttp://gslc.genetics.utah.edu/units/basics/tour/inheritance.swfhttp://science.nhmccd.edu/biol/genetics.htmlhttp://library.thinkquest.org/20465/games.htmlhttp://library.thinkquest.org/20465/games.htmlhttp://library.thinkquest.org/20465/games.htmlhttp://library.thinkquest.org/20465/games.htmlhttp://science.nhmccd.edu/biol/genetics.htmlhttp://gslc.genetics.utah.edu/units/basics/tour/inheritance.swfhttp://gslc.genetics.utah.edu/units/basics/tour/inheritance.swfTop Related