Genetics
Ms. Gunjan M. Chaudhari
• The passing on of characteristics (traits) from parents to offspring
••GeneticsGenetics: The scientific study of heredity: The scientific study of heredity
Heredity :
UNIT 1 Introduction to genetics
•• Understanding hereditary diseases and to develop Understanding hereditary diseases and to develop
new treatmentsnew treatments
•• Donor matchesDonor matches
•• PaternityPaternity
•• ForensicsForensics
•• EvolutionEvolution
Importance of geneticsImportance of genetics
1.1. Microbial geneticsMicrobial genetics--
2. Mycogenetics2. Mycogenetics--
3. PIant genetics3. PIant genetics--
4. Animal genetics4. Animal genetics--
5. Human genetics5. Human genetics--
6. Population genetics6. Population genetics-- genetics of the different genetics of the different
populations of animal and plant species.populations of animal and plant species.
7. Cytogenetics7. Cytogenetics--It provides the cytological It provides the cytological
explanations of genetical principles.explanations of genetical principles.
8. Biochemical genetics8. Biochemical genetics--It provides the biochemical It provides the biochemical
explanations of various genetical phenomena. explanations of various genetical phenomena.
Branches of geneticsBranches of genetics
9. Molecular genetics9. Molecular genetics-- interprets most genetical phenomena in the term of interprets most genetical phenomena in the term of
chemical molecules.chemical molecules.
10. clinical genetics10. clinical genetics-- genetical analysis in diagnosing various hereditary genetical analysis in diagnosing various hereditary
diseases in man and suggests the possible cures for them. diseases in man and suggests the possible cures for them.
11. Developmental genetics11. Developmental genetics-- genetical knowledge to the developmental genetical knowledge to the developmental
biologybiology
. .
12. Radiation genetics12. Radiation genetics-- genetical effects of radiations on the living genetical effects of radiations on the living
organisms.organisms.
13. Quantitative or biometric genetics13. Quantitative or biometric genetics-- inheritance of quantitative traits such inheritance of quantitative traits such
as body weight, mature plant height, egg or milk production records, yield of as body weight, mature plant height, egg or milk production records, yield of
grain per acre, etc.grain per acre, etc.
14.Ecological genetics14.Ecological genetics-- genetics of ecological phenomenagenetics of ecological phenomena
Branches of geneticsBranches of genetics
Who was Gregor Mendel?
• Austrian monk who studied mathematics and science
The Father of Genetics:
Gregor Mendel(1822-1884)
* born into a poor peasant family (ethnic minority)
* as youth, placed in Catholic monastery
The Father of Genetics:
Gregor Mendel(1822-1884)
* between 1853-1867taught high schoolbiology, and in hisspare time experimented with pea plants
Mendel’s Experiments:
* established * established genetics as a science.as a science.
** combined careful combined careful experiments withwithmathematical analysis analysis
** were were ignored, along with his ideas, during, along with his ideas, duringhis lifetimehis lifetime
Gregor MendelGregor Mendel•• Austrian Monk.Austrian Monk.
•• Experimented with “pea plants”.Experimented with “pea plants”.
•• Used pea plants because:Used pea plants because:–– They were availableThey were available
–– They reproduced quicklyThey reproduced quickly
–– They showed obvious differences in the traitsThey showed obvious differences in the traits
Understood that there was something that Understood that there was something that carried traits from one generation to the carried traits from one generation to the nextnext-- ““FACTORFACTOR”.”.
Mendel was fortunate he chose the Garden Pea
•Mendel probably chose to work
with peas because they are
available in many varieties.
•The use of peas also gave Mendel
strict control over which plants
mated.
•Fortunately, the pea traits are
distinct and were clearly
contrasting.
Genetic Information
• Gene – basic unit of genetic information. Genes determine the inherited characters.
• Genome – the collection of genetic information.
• Chromosomes – storage units of genes.
•• DNADNA - is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life
Mendelian GeneticsMendelian Genetics•• DominantDominant traitstraits-- traits that are traits that are
expressed.expressed.
•• RecessiveRecessive traitstraits-- traits that are covered traits that are covered up.up.
•• AllelesAlleles-- the different forms of a the different forms of a characteristic.characteristic.
•• GenotypeGenotype-- the types of genes (Alleles) the types of genes (Alleles) present.present.
•• PhenotypePhenotype-- what it looks like.what it looks like.
•• HomozygousHomozygous-- two of the same alleles.two of the same alleles.
•• HeterozygousHeterozygous-- two different alleles.two different alleles.
Phenotype & GenotypePhenotype & Genotype
• Phenotype - the way an organism looks
• genotype - the gene combination of an organism
Genotype
Phenotype
Dominant vs. Recessive
• A dominant allele is expressed even if it is paired with a recessive allele.
•A recessive allele is only visible when paired with another recessive allele.
Heterozygous & Homozygous
• Heterozygous - if the two alleles for a trait are different (Aa)
• Homozygous - if the two alleles for a trait are the same(AA or aa)
An allele:An allele: is one of two or more
alternatealternate forms of a gene
allele
An allele:An allele: is one of two or more
alternatealternate forms of a gene
What is a monohybrid cross?
• Monohybrid cross - A cross between two
individuals involving to observe inheritance of
one trait
• Hybridization terminology
• P generation – True breeding parents
• F1 generation – First generation offspring;
resulting from a cross between pure breeding
individuals (parents)
• F2 generation – Second generation offspring;
resulting from a cross between F1 plants
Mendel used a monohybrid cross
• F1 generation peas had
purple flowers
• F2 generation peas
consisted of mostly purple
flowers (3/4) and small
number of white flowers
(1/4)
• Why?
Results of Mendel’s monohybrid cross
F1
F2
So, what is the mechanism of inheritance?
• Genes code for traits, each gene has two different forms called alleles
• Law of segregation –Alleles separate during meiosis; sperm and egg possess one allele for every gene
• Genotype – Combination of alleles one has
Mendel’s experiments showed that purple
flower color is dominant over white
So, what is the mechanism of inheritance?
• Genotype – Combination of alleles one has
• Two forms of alleles –DOMINANT and recessivealleles
• Two alleles = two possible phenotypes
• Phenotype – Outward appearance expressed by a gene
• Dominant vs. recessive… what’s the difference?
Mendel’s experiments showed that purple
flower color is dominant over white
Punnett square
• Letters represent alleles,
typically the first letter of a
word that defines a trait
• Capital P for purple
(dominant trait) , lowercase
p for white (recessive trait)
• Genotypes are either
homozygous or
heterozygous
Punnett square
Punnett square
• Punnett square – A tool
developed by Reginald
Punnett used to predict the
number and variety of genetic
combinations
• Homozygous – Having the
same two alleles for one gene
(either both dominant or both
recessive)
• Heterozygous – Having two
different alleles for one gene
(one dominant allele, and one
recessive allele)
Reginald Punnett
Dihybrid crossing
• Mendel did not know if 2+
traits were inherited together
or separately
• If inherited together
phenotypic ratio of the F2
generation would be 3:1
(dependent assortment)
• In other words, were
dominant alleles inherited
together and were recessive
alleles inherited together?
Dihybrid crossing
• Dihybrid cross –
Breeding individuals
having for to observed
inheritance of two
different traits
• For example, seed color
(yellow, green) and seed
texture (round, wrinkled)
• Independent assortment
– each pair of alleles
segregates
independently of the
other pairs of alleles
during crossing.
F1
F2
P
29
Mendel’s Law of Dominance
C. Law of Dominance
1. Of two contrasting
characteristics, the dominant
one may completely mask
the appearance of the
recessive one.
Incomplete Dominance
• In incomplete dominance, neither allele
is __________ so there is a blending of
______ when two different alleles for
the same trait occur together.
• Colors blendblend together
• (______________
individuals =
3rd phenotype)
dominantdominanttraitstraits
heterozygousheterozygous
red whitepink
Incomplete Dominance
• In Four O’ Clocks, if you cross a red RR
(which is always pure) with a white WW
(that is also always
pure) , you get a
pink RW (which
is always hybrid /
heterozygous
Incomplete Dominance
• Cross of two pink flowers
RW X RW
• What are gamete possibilities?
• genotype ratio
1RR : 2RW : 1WW1RR : 2RW : 1WW
• phenotype ratio
1red : 2 pink : 1 white1red : 2 pink : 1 white
R
R
W
W
RW
white
RR
red
RW
pink
RW
pink
Codominance
• Both allele contribute to the phenotype of the organism by showing up simultaneously (at the same time) in heterozygous individuals.
• In cattle and horses, if you cross a pure _ RR _ with a pure __ WW you get (RW) which produces the color __roan___.
• These cattle or horses actually have both red and white hairs intermixed, or are spotted. Roan is a third _phenotype__________.
•
Codominance
• Andalusian chickens also show this
pattern of inheritance.
• If you cross a black (BB) chicken
• With a white (WW) chicken
• You get black+white speckled (BW) chicken
Law of segregation
Why do traits “disappear” in one generation only
to reappear in a subsequent generation?
Each plant possesses two distinct separable
units (alleles) for each trait inherited from
each parent.
Gametes contain ONE allele for each trait.
The two alleles for a trait must separate
when gametes are formed
The unit (allele) does not disappear.
It may be present but hidden.
Mendel's Law of
Independent Assortment
Definition: The principles that govern heredity were discovered by a monk named Gregor Mendel in the 1860's. One of these
principles, now called Mendel’s Law of Independent Assortment, states that allele
pairs separate independently during the formation of gametes. This means that
traits are transmitted to offspring independently of one another.
References:
1. www. iteachbio.com
2. www. slideworld.com
3. www. step.nn.k12.va.us
4. www.clfs.umd.edu
5. www.hos.ufl.edu
6. www.biol.unt.edu
7. http://www.unit5.org/villhauer/Biology/Power%20Points/Mendeli
an%20Exceptions%2011-3.ppt#257,2,Mendel’s Principles
Revisited
8. http://woodwardsworld.org/uploads/Genetic_Fundamentals___
Gregor_Mendel.ppt#277,56,Mendel’s Law of Dominance
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