A- Pedigree (family tree)

Scientists find it hard to study the inherited traits and their transfer to human due to:-

- The long time period between one generation and another.

- The small number of individuals resulted from every marriage

So, scientists study some hereditary traits in human by studying the pedigree (family tree) of some families

Pedigree: Hereditary data represented in the form of chart diagram which explains how a certain trait is inherited, and used in tracking different hereditary traits

Importance of pedigree

1- It explains how a certain trait is inherited in a certain family

2- It is used to trace different hereditary traits (especially those linked to genetic diseases and disorders)

3- It is used for prediction of the probability of appearance of these traits in coming generations.

The following chart describes pedigree of a family

Fig. (12) Pedigree chart

- Male individuals are denoted by squares

- Female individuals are denoted by circles

- Mating (marriage) is symbolized by a line joining between the circle and square

- Offspring is symbolized by a vertical line extending from that of marriage

- Every generation is given a Roman number (I – II – II – V…etc)

- Every individual is given a number, in order to facilitate finding it

- Shaped which are studies are coloured (in the previous chart, father (1) of generation (I) is the individual being studied)

The study of genetic cases in human

1- Albinism ( also called Albino or Sun enemy)

Albinism: Genetic disorder which causes the absence of melanin pigments from the cells of hair, eye lashes and skin.

à Albinism is caused by the recessive gene (a)

Fig. (13) Pedigree chart of albinism Fig. (14) Child with Albinism

Probable genotypes of this family members are:-

Generation (I)

1- Aa 2- Aa

Generation (II)

1- aa 2- AA or Aa 3- AA or Aa 4- AA or Aa

2-Polydactyl

Polydactyl: Genetic disorder in which human has sixth fingers (instead of five), it is caused by a dominant gene

Fig. (14) Polydactyl genetic disorder

Дата добавления: 2015-10-23