INTRODUCTION TO GENETICS &GENETIC COUNSELLING

Question 1

What’s Human genetics

Answer 1

Human genetics is the scientific study of variation in humans

Question 2

What are Genes?

Answer 2

Genes:These are sequences of DNA and hereditary elements
that carry traits and genetic intructions in humans

They are usually found in chromosones

Question 3

What are Alleles

Answer 3

Alleles: These are variants of genetic instructions being
Carried by the genes

Question 4

What are Chromosones

Answer 4

Chromosones: These are custodians of the genes. In human,
There are 23pairs of chromosones .
These consist of

22pairs of autosomal chromosones + one XY pair in Male

22pairs of autosomal chromosones + one XX pair in Female

Question 5

When is it said for a person to be heterozygote for a gene?

Answer 5

If the member of a gene pair carry different instruction the
person is heterozygote for that gene e.g AS, the resulting trait may be determined by one member of the pair known as the
DOMINANT gene the other pair that is not manifested is known
as the RECESSIVE gene

Question 6

What is Referred to as a KARYOTYPE?

Answer 6

Each individual has a chromosome that is characteristic in number and form

Question 7

What is a Karyogram?

Answer 7

Karyogram
–Is the photographic representation of stained chromosomes arranged in order of decreasing length.

Question 8

Much of what we know about genes was first discovered by?

Answer 8

Gregor Mendel

Question 9

He Conducted experiments on?

Answer 9

the garden pea (Pisum sativum)

Question 10

What was key to Mendel’s success? And why?

Answer 10

Garden peas also produce a large number of offspring, a key to Mendel’s success.

Question 11

What are the 3 Mendel’s Laws?

Answer 11

Inheritance is particulate: “particles” called genes carry the information that makes parents tend to resemble their offspring.

–These “particles” segregate, so that individuals with two particles produce gametes with only one particle, the law of segregation.

–The “particles” for each gene segregate independently of each other, the law of independent assortment.

Question 12

Phenotype vs. Genotype

Answer 12

An individual’s PHENOTYPE is his/her observable characteristics.
An individual’s GENOTYPE is his/her genetic composition of alleles.

Question 13

The effect of every gene depends both upon the environment, and upon other genes
true or false

Answer 13

TRUE

Question 14

Traditionally - 3 types of diseases
Namely?

Answer 14

a)genetically determined
b)environmentally determined
c)1. + 2.

Question 15

up to ?% of pediatric in-patients have genetic abnormality

about ?% of spontaneous abortuses have chromosomal aberration

Answer 15

20%
50%

Question 16

CLASSIFICATION GENETIC DISEASES

Answer 16

a)Chromosomal disorders
b)Single gene diseases
c)Mitochondrial disorders
d)Polygenic disorders

Question 17

Autosomal recessive inheritance
characteristics (4)

Answer 17

Affected persons are usually born to unaffected parents

Parents of affected persons are usually asymptomatic but carry a single gene defect

Risk is increase in consanguinity

Children of both parents who are both heterozgous for the mutated gene have 25% chance of inheriting the disease

Question 18

Autosomal recessive inheritance
Examples ?

Answer 18

cystic fibrosis
sickle cell anaemia
Tay-Sachs disease
Phenylketonuria
Mucopolysaccharidoses
Glycogen storage diseases
Galactosemia

Question 19

Autosomal dominant
characteristics?

Answer 19

Affected person usually has at least one affected parent

It affects either sex

Affected person has 50% chance of passing the defect on to their children

Question 20

Autosomal dominant
Example?

Answer 20

Achondroplasia
Huntington disease
Marfan syndrome
Familial hypercholesterolemia
Ehlers-Danlos syndrome
Polycystic kidney disease
Hereditary spherocytosis

Question 21

X-LINKED RECESSIVE INHERITANCE
characteristics (3)

Answer 21

Affects males almost exclusively

Affected males are usually born to unaffected parents as mother is usually asymptomatic carrier, although she may have affected male relative.

There is no male to male transmission of the defect

Question 22

X-LINKED RECESSIVE INHERITANCE
examples? (dch)

Answer 22

Duchene muscular dystrophy and
Colour blindness,
haemophilia

Question 23

X-LINKED DOMINANT INHERITANCE
characteristics?

Answer 23

Affects either sex

females are often more mildly and variably affected than males

The child of an affected female has a 50% chance of being affected regardless of sex

All the daughters but none of the sons of affected male will be affected

Question 24

X-LINKED DOMINANT INHERITANCE
characteristics?

Question 25

X-LINKED DOMINANT INHERITANCE
Example ?

Answer 25

vitamin D resistant ricket
hypophosphatemic rickets
Klinefelter Syndrome
Incontinentia Pigmenti
Rett syndrome

Question 26

X-LINKED DOMINANT INHERITANCE
Example ?

Answer 26

vitamin D resistant ricket
Klinefelter Syndrome
Incontinentia Pigmenti
Rett syndrome
hypophosphatemic rickets
Klinefelter Syndrome

Question 27

Y-LINKED INHERITANCE
xtics? (4)

Answer 27

Would only affect males

Affected males would always have affected fathers

All the sons of affected father would be affected

As females are perfectly normal without Y gene, this code for either non-essential characters or for male specific functions.

Question 28

Y-LINKED INHERITANCE
examples?

Answer 28

HYPERTRICHOSIS PINNAE (hairy ears)

Question 29

GENETIC COUNSELLING
Definition:

Answer 29

This is communication of information and
advice about inherited condition

Question 30

The person seeking the genetic advice (usually the parent or a guardian) is called the ?

Answer 30

CONSULTAND

Question 31

The affected individual who caused the “person seeking the genetic advice” to seek the advice is called the ?

Answer 31

PROBAND, who is usually the child but the child may also be the CONSULTAND If of age

Question 32

PURPOSE OF GENETIC COUNSELLING
(5)

Answer 32

1. To provide concrete and accurate information about inherited Dxs
2. Reassure worried parents about the inherited condition
3. Allows affected parties to make informed decision on inherited Dxs
4. Educate parents/people about the mode of inheritance
5. To offer supports to affected families by health professionals

Question 33

PLEASE NOTE THAT COUNSELLING SHOULD NOT BE?
(2)

Answer 33

A one-way discussion, After the health professional gives information he should thereafter listen to the views of affected parties

It should not be directional i.e Telling them what to do. The affected parents decide steps to take the professional should guide them to make the best decision.

Question 34

PROCESS OF GENETIC COUNSELLING
(5)

Answer 34

History taking & pedigree construction
Examination of the Proband
Diagnosis making & Treatment
Counselling
Follow-up

Question 35

Rules of pedigree construction?
(5)

Answer 35

a) Standardised symbols are used
b) By convention the male lines are placed on the LEFT
c) Female lines are placed on the RIGHT
d) All members of same generation are place on same line
e) Roman numerals are used for each generation

Question 36

physical examination, The physician should? 6things

Answer 36

Look for dysmorphic features

Describe them accurately

Important anatomical landmarks used in description

Recording of the dermatoglyphics is important

Consider the summing up of the features in a syndrome
Consider consulting computerised database on
Dysmorphology or Encyclopedia on human malformation
for accuracy of tagged syndrome in the proband

Question 37

useful investigations used in genetic counselling?

Answer 37

Chromosonal analysis: Karyotyping
DNA analysis: Polymorphisms & sequencing studies
Biochemical assays
Histopathology studies
Imaging studies

Question 38

Rules of counselling?
7 rules

Answer 38

1. This should take place under conducive and friendly environment
2. Adequate time should be allocated to it
3. should involve all aspects of the condition
4. The education level of consultands should tailor the discussion, use lay languages if poorly educated
5. Recurrence risks/ frequencies should be told
6. Guilt & perceived stigma should be dealt with
7. Reproductive options should be offered to the consultands

Question 39

examples of Reproductive options that should be offered to the consultands?

Answer 39

Further pregnancy ± PRENATAL DIAGNOSIS

Artificial insemination by donors

In vitro fertilisation ±PRE IMPLANTATION DIAGNOSIS

Adoption

Contraception

Question 40

Follow up?

Answer 40

1. This is important in order to re-inforce the counselling
2. Follow up on the clinical state of patients
3. Allows for the physician to give information about new opportunities that could have emerged after the diagnosis
   Such as;
   New diagnosis tools
   Treatment regimen
   Preventive strategies etc.