Genetics

• The study of heredity .• Gregor Mendel- Austrian Monk -

Father of modern genetics• Studied inheritance of characteristics

in green pea.

Heredity

• The transmission of inherited characters from one generation to another.

• Each characteristic is called a trait.

Gene

• Are unit of heredity.• factor that control traits.• composed of DNA• Allele: a pair of genes located at the same

place on a homologous chromosome• Dominant genes: those that mask the

presence of other corresponding genes• Recessive genes: those whose physical

expression (phenotype) is masked in the presence of a dominant gene.

• Phenotype: the physical appearance of a plant or animal because of its genetic makeup (genotype)

• Genotype: genetic constitution (makeup) of an individual

• Phenotype could be –Brown eyes .• Genotype would be BB.

Types of genotype

• Heterozygous- when a plant or animal has two genes for different traits (example: tall and short)

• Homozygous- when a plant or animal has two genes for the same trait (example: two tall genes, or two short genes

Chromosomes

• A chromosome is an organized structure of DNA and protein found in cells.

• Contains 50% proteins and 50% DNA (deoxy-ribonucleic acid).

• Made of many chromatin threads• Somatic cells contain 46 chromosomes,

gametic cells contain 23 chromosomes.• 44 of our chromosomes are AUTOSOMES,

while 2 are called sex chromosomes.• Each chromosome contains many GENES

that act as a blueprint or set of instructions for the cell.

DNA

• The DNA in chromosomes forms the basis for the genetic code

• DNA is made of long chains of nucleotides. • DNA has a DOUBLE-HELIX structure where 2 strands

of nucleotides join and twist around to form a spiral staircase or twisted ladder.

• Each nucleotide has 3 parts:• 1. a phosphate group - helps form the backbone of

the DNA molecule• 2. a sugar (deoxyribose) - acts as a glue,forms the

backbone with phosphate• 3. nitrogen bases - 4 types (guanine, cytosine,

adenine, thymine)

DNA FUNCTION

• Control of cell activities• Replication• Undergo mutations

Mitosis

• The process of equal partitioning of replicating chromosomes into identical groups.

• Stages : interphase, prophase, metaphase, anaphase, telophase and cytokinesis.

Meiosis –reduction division

• Takes place in gamete or sex cells.• There is double division maintaining

the DNA but reducing the chromosomal count to 23.

• Meiosis I and Meiosis II

MENDELIAN LAWS

Law of DominanceLaw of Segregation  Law of Independent Assortment

LAW OF DOMINANCE

• Mendel’s first law of inheritance• If two alleles are different i.e.

heterozygous ,the trait associated with only one of these will be visible (dominant) while the other will be hidden(recessive)

LAW OF SEGREGATIONThe separation of allele into separate

gametes is law of segregation. It states that every individual possesses a

pair of alleles (assuming diploidy) for any particular trait and that each parent passes a randomly selected copy (allele) of only one of these to its offspring.

LAW OF ASSORTMENT

Also known as "Inheritance Law”

It states that separate genes for separate traits are passed independently of one another from parents to offspring

Genetic disease

• Is an abnormal condition that a person inherits through genes or chromosomes.

• Caused by mutations.

Genetic disease

MULTIFACTORIAL DISORDERS

• Also known as Complex disorders.• Associated with the effects of multiple

genes in combination with lifestyles and environmental factors.

• eg.AsthmaCancersCleft palateDiabetesHeart diseaseHypertension

MENDELIAN DISEASES

Mendelian diseases are inherited according to the Mendelian Laws.

Dominant Recessive Sex linked diseases

AUTOSOMAL DOMINANT Individual with an autosomal dominant

trait will produce two kinds of gametes with respect to the mutant gene.

Half with the mutant gene and half with the normal allele.

Offspring of such individual has a 50:50 chances of being affected, provided the other parent is normal.

DOMINANT DISEASES

Polycystic kidney

Neurofibromatosis

Retinoblastoma

Marfan syndrome

AUTOSOMAL RECESSIVE• Abnormalities occur when both the

parents are heterozygous.• Offspring of such parents has a chance

of 1:4 being affected.

RECESSIVE DISEASESCystic fibrosisSickle cell anemiaGalactosemiaPhenylketonuria

SEX LINKED • A mutant gene on X chromosome in

males will express itself readily as there is no normal allele

• A mutant gene on X chromosome in females will not express itself in the presence of normal allele.

SEX LINKED DISEASESHemophiliaColor BlindnessG6PD Deficiency

Chromosomal abnormalities

• Incorrect number of chromosomes. nondisjunction : chromosomes do not

separate properly. Eg trisomy monosomy

Breakage of chromosomes:DeletionDuplicationInversionTranslocation

Examples of chromosomal disorder

• Down syndrome: trisomy 21• XXY :klinefelter syndrome male• XXX :trisomy female• XYY: Jacobs syndrome male• XO: Turner syndrome.

GENETIC PREDISPOSITION

• Also known as genetic susceptibility, genetic risk• Genetic predisposition is an inherited risk of developing a

disease or condition.• Having a genetic predisposition for a disease does not

mean that you will get that disease, but your risk may be higher than that of the general population.

• Genetic testing is able to identify individuals who are genetically predisposed to certain health problems

Preventive and Social measures• (a) Eugenics Galton proposed the term eugenics

for the science, which aims to improve the genetic endowment of human population. Eugenics has both negative and positive aspects.

Negative eugenics The aim of negative eugenics is to

reduce the frequency of hereditary disease and disability in the community to the least possible degree.

Positive eugenics It seeks to improve the genetic

composition of the population by encouraging the carriers of desirable genotypes to assume the burden of parenthood.

• (b) Euthenics Studies with mentally retarded (mild)

children indicated that exposure to environmental stimulation improved their IQ. Thus the solution of improving the human race does not lie in contrasting heredity and environment, but rather in mutual interaction of heredity and environmental factors. This environmental manipulation is called euthenics and has considerable broader prospects for success

• (c) Genetic Counseling The most immediate and practical service

that genetics can render in medicine and surgery is genetic counseling.

] Genetic Counseling may be Prospective Retrospective

• Most genetic counseling is at present retrospective i.e. the hereditary disorder has already occurred with in the family

• The WHO recommends the establishment of genetic counseling centres in sufficient numbers in regions where infections disease and nutritional disorders have been brought under control and in areas where genetic disorders have always constituted a serious public health problem (i.e. sickle cell anaemia and thalassemia)

• The methods which could be suggested under retrospective genetic counseling are:

• Contraception• Pregnancy termination Sterilization depending upon the attitudes and

cultural environment

• Other genetic measures Consanguineous marriages: When

blood relatives marry each other there is an increased risk in the offspring of traits controlled by recessive genes, and those determined by polygenes.

Examples are : Albinism, Alkaptonuria, Phenylketonuria and several others

Prenatal Diagnosis: Amniocentesis in early pregnancy

(about 14-16 weeks) has now made it possible for prenatal diagnosis of conditions associated with chromosomal anomalies. EXAMPLE Down’ s syndrome

Indications for pre-natal diagnosis

Indications Methods

Advance maternal age ,previous child with chromosome aberration, intrauterine growth delay

Cytogenetics (amniocentesis , chorionic villus sampling)

Biochemical Disorders Protein essay, DNA diagnosis

Congenital Anomaly Sonography, foetoscopy

Screening for neural tube defects and trisomy

Maternal serum alpha-foetoprotein and chorionic gonadotropin

Prevention Of Genetic Diseases: How Genetic Testing Can Save Child's Life

• Genetic tests performed on newborns and children can help parents prepare their child for the possibility of developing a hereditary disease. DNA tests can tell parents many things about a child's genetic makeup, including whether or not they currently have a genetic disorder or whether they are at risk for developing an inherited disease later in life.

• Genetic testing often begins in the womb. Doctors can administer prenatal DNA tests to detect certain genetic disorders, such as Down syndrome, as well as numerous fatal birth defects.

• A technician uses a needle to lightly prick your baby 's heel and draw blood. This kind of early attention to genetic information can literally save a child's life, as disease prevention or treatment can often begin immediately.

Newborn Screening• Preventing genetic disorders once the child has been

born can be helped through newborn screening. This typically involves taking a sample of blood from the baby's heel.

• Genetic testing is done in all hospitals to test for a variety of metabolic disorders before symptoms arise. These disorders can potentially lead to severe mental retardation and even death.

• If a genetic disorder is detected, metabolic or otherwise, treatment can begin immediately to prevent complications and to ensure that your child has the best possible chances for living a normal, healthy life.

• A more thorough list of conditions looked for with genetic testing and their possible preventative measures can be found on the KidsHealth.org article on newborn screening tests

• Recognizing Pre-clinical areas Screening tests are available for the

early diagnosis. Example- Heterozygotes for

phenylketonuria can be detected by a phenylalanine tolerance test

Detection of Genetic carriers Especially the inborn errors of

metabolism The female carriers of Duchenne type

of muscular dystrophy, an X- linked disorder can now be detected by elevated levels of serum creatine kinase in 80 percent of carriers.

• Specific protection Increasing attention is now being paid to the

protection of individuals and whole communities against mutagens such as X-rays and other ionizing radiations and also chemical mutagens.

Need of individualized and specific education about how to:

• Check regularly for the disease.• Follow a healthy diet.• Get regular exercise.• Avoid smoking tobacco and too

much alcohol.• Get specific genetic testing that

can help with diagnosis and treatment.

Conclusion• Disease prevention is an integral part of

parenthood, and prevention of genetic disorders can help us take this one step further to ensure that the child lives the healthiest life possible.

ARSHPREET KAUR SONALGURPREET KAUR