genetics - kcesmjcollege.inwhy do traits “disappear” in one generation only to reappear in a...

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