CONCEPT OF INHERITANCE

BASED ON MENDEL’S

EXPERIMENT

The heredity factor that determines a

particular characteristics is called gene

Gene is the basic unit of inheritance that

determines a particular characteristic in

An Organism

The gene controlling a particular

characteristic exists in pairs called allele

The transmission of characteristics from the

parents to the offsprings from generation to

generation is called inheritance

A trait is the variant for a specific

Characteristics

Characteristics Trait

Height Tall & short

Color of the seed Yellow & green

Seed shape Round & wrinkled

Allele is an alternative form of a gene that

occupies the same locus on the homologus

Chromosomes

Alleles can exist in dominant and recessive

Forms Dominant allele will express itself and

display the dominant trait of the

characteristic only when both alleles are

dominant or at least one dominant allele is

present

A recessive allele will only express itself in

the absence of a dominant allele

Phenotype : physical appearance

Genotype : genetic composition

Homozygote :

organism with two identical alleles

Heterozygote :

organism with two different alleles CD

MENDEL’S FIRST LAWA characteristics of an organism is determined by a pair of alleles. In the formation of gamete, the pair of alleles segregate during meiosis I and only one of each pair of alleles can be present in a single gamete

Each characteristic of an organism iscontrolled by allelesDuring the formation of gamete, the two factors will separate and each gameteonly has one factor

MENDEL’S SECOND LAW

Dihybrid inheritance : involve two differentCharacteristics

The segregation of alleles for seed shapedoes not affect the segregation of allelesFor seed colorThe alleles for each characteristic segregateindependently of one another resulting in The production of gametes with differentAllele combinations

UNDERSTANDING KEY IDEAS

1. Flower color is characteristic of a plant

2. One characteristic is determined by a pair of allele

3. Dominant trait is expressed when both alleles are recessive

4. The genotype for dominant trait can be homozygous dominant or heterozygous

5. Allele is a gene on homologous chromosome

6. Recessive allele is represented by a capital letter

7. When a genetic cross is made between a tall and a dwarf pea plant, both of which are purebreds, the F1 generation produced are all tall stemmed plants

8. A parent with heterozygous genotype for both characteristics will produce four types of gametes

9. The phenotypic ratio for the offspring in F2 generation of a dihybrid cross is 3:1

A farmer has three types of plants, O, P and S. Plants O and P produce red

flowers while plant S produces white flower. The farmer carried out cross

pollination between plant O and S. Red-flowered plants were produced.The

farmer also cross-pollinated plant S and plant P in which both white and red

flowers were produced.

a) Which plant has a heterozygous genotype?

b) Draw a genetic diagram to show the cross between plant S and plant P.

c) What is the phenotypic ratio of the F1 generation.

d) What is the genotype of plant S?

e) Name the genotype of plant S?

f) If the offsprings from the cross between plant O and plant S were self pollinated, what would be the genotypic ratio and phenotypic ratio of the offsprings produced?

g) Draw a Punnett square to show the result of the cross in (f)

h) What is the name of the inheritance for the genetic cross between the plants O, P and S ?

i) Explain the Mendel’s Law which is related o this type of inheritance.

answera) Plant Pb) 1 red flowered plant : 1 white flowered plantc) rrd) Homozygous recessivee) Genotype ratio 1RR : 2Rr : 1rrf) Phenotypic ratio 3 red flowered plant : 1 white flowered plant

Monohybrid Inheritance Mendel’s First Law : states that a pair of alleles control a particular characteristic. In the formation of gametes,the alleles segregateand only one allele present in one gamete

Gametes R r

R RR Rr

r Rr rr

Inheritance of ABO Blood Group System

Controlled by 3 alleles,

1. allele A causes antigen A to be formed

2. Allele B causes antigen B to be formed

3. Allele O does not cause any antigen

to be formed

4. Blood Group AB causes both antigen A and B to be formed

Allele A and B are dominantAllele O is recessive

Example of ABO blood group inheritance in Humans

1. Illustrate schematic diagram genetic cross between parents of blood group A (Heterozygous) and blood group B (homozygous dominant)

2. Illustrate schematic diagram genetic cross between parents of blood group AB (Heterozygous) and blood group O (homozygous recessive)

Rhesus Factor : Rh factor (antigen)

Rhesus positive (Rh +) : individual with Rh factor(DOMINANT) : Rh

Rhesus negative (Rh -) : without Rh factor(RECESSIVE) : rh

Example : Rhesus positive (heterozygous) geneticcross with Rhesus negative (homozygous recessive)

Foetal’s blood (Rh +) mixed with mother’s blood (Rh - )

Mother’s antibodies will be produced (lymphocytes)

Agglutination/lymphocytes

Anaemia, jaundice, damage to heart, liver

Autosomes and sex chromosomes

Autosomes : chromosomes that do not have

the genes to determine the sex.

SEX CHROMOSOMES :

Two types : X and Y

Female : 22 + X (GENOTYPE 44 + XX)

Male : 22 + X / 22 + Y (GENOTYPE 44 + XY)

Sex Determination

Draw a schematic diagram

sex determination in humans

Sex-linked Inheritance

Examples : haemophilia and color blindness

Haemophilia : recessive allele (h) located on the X chromosome Xh

Blood clotting is controlled by Dominant allele XH

Example : Male normal blood clotting cross genetic with

Female normal blood clotting (carrier)

Color Blindness : recessive allele (b) located

on the X chromosome : Xb

Normal color vision is controlled by Dominant allele XB

Example : Male color blind cross genetic with

Female normal color blind (carrier)

HEREDITY DISEASE

Disease that offspring inherit from their parents

Hereditary disease can be from

defective genes linked to X chromosomes

Defective genes located at the autosomes ( Albinisme, Sickle Cell anaemia, thalessemia)

ALBINISME

Defective allele which controlled the

synthesis of melanin pigment

Affected body parts lack of melanin pigment

Sickle Anaemia CellDefective allele which is involved in the synthesis of haemoglobinLocated in an autosomCause the red blood cells to be in the shapeof a sickle, more fragile, break easily, thenagregate together to clog blood capillaries

Poor circulations

THALASSAEMIABlood disorder that disrupts the production of

haemoglobin in red blood cells

(T major / T minor )

Symptoms : paleness, jaundice, enlarged spleen, liver and heart

Incurable disease

Need regular blood transfusions

Treatment : lead to iron overload

STRUCTURE OF DNABasic unit :

nucleotides

guanine

Nitrogenous base

Phosphategroup

Deoxyribose sugar

cytosine thymineAdenine

Each nucleotide is

joined to form long

polynucleotide

Two polynucleotide will

be linked together at the

nitrogenous base by

hydrogen bond

Thymine = Adenine

Cytosine = Guanine

DNA consists of two polynucleotide strands coiled, forming a double helixProposed by : Watson and Crick

GENETIC KNOWLEDGE is used in the following fields

SELECTIVE BREEDING

GENETIC ENGINEERING

DNA FINGERPINTINGHUMAN GENOME PROJECT

DNAFINGERPRINTING