UNIT 6: HUMAN GENETICS

INDEX1. Inheritance and Human Variation2. Diagnosis of Genetic Diseases3. Human Genetic Disorders

1. Inheritance and HumanVariation

The characteristics

of the individuals

depend on two factors:

Genetic traits

Genotype

Inherited

Environmental factors (food,

lifestyle habits…)

Phenotype

Usually not transmissible

Types of traits

Quantitative

Skin colour

Eyes colour (they have a range of

possible expressions)

Qualitative Examples of quantitative traits: skin and eyes colour

Qualitative traits in humanbeings

Dominantallele

Recessiveallele

Curly hair Straight hair

Ability to roll the tongue

Inability to roll the tongue

Thick lips Thin lips

Long eyelash Short eyelash

Detached earlobes

Attached earlobes

Blood group A and B

Blood group 0

Blood groupRh+

Blood groupRh-

Straight and curly hair

The ABO system establishes four blood groups (A, B, AB and O) according to the presence or absence of certain proteins, called A and B, in the membrane of the red blood cells.

Antibodies react against specific antigens destroying them.

Phenotypes Group A Group B Group AB Group 0

Genotypes AA BB AB 00

A0 B0

Alleles A and B are codominant.Alleles A and B are dominant over allele 0, which is recessive

Rh System

Rhesus factor is another antigen which can be present (Rh+) or not (Rh-) inthe red blood cells.

Rh+ is dominantRh- is recessiv

Blood typing virtual lab:http://www.nobelprize.org/educational/medicine/bloodtypinggame/gamev2/index.html

Page 109 activity 3, 4, 5, 9

Phenotypes Rh+ Rh-

Genotypes Rh+Rh+ Rh-Rh-

Rh+Rh-

Erytroblastosis fetalis: http://education-portal.com/academy/lesson/rh-blood-group-rh-factor-erythoblasotis-fetalis.html

AB- group

Test tubes containing the corresponding antigen

A double homozigous 0+ woman decides to have a baby with a A- man, whose father was 0-.What is the probability to obtain an A- baby?

00Rh+Rh+ x A0Rh-Rh-

From the father

ARh- 0Rh-

0Rh+ A0Rh+Rh- 00Rh+Rh-

Sol.: 0% (none of the babies will be Rh negative)

2. Diagnosis of Genetic Diseases

Amniocentesis

Foetus cells from the amniotic fluid are extracted with a needle. The DNA isanalysed and possible chromosom or metabolic disorders are detected

Recommendation foramniocentesis

Couples already witha child with a chromosome

anomaly

Parents’ family withgenetic disease

Pregnant womenover 35 years old

3. Human Genetic Disorders

Autosomal dominant (A)

Autosomal recessiv (a)Linked to the X chromosomeDaltonism, haemophilia

4. Some examples of Pedigree Charts

• At least 3 generations• Phenotype coloured• Indicate genotypes• Indicate type of allele• Include cousins

Autosomal dominant