Question

-Huntington's

Answer 1

A pedigree is the representation of family history. 1) I.1, II.2, II.3, II.7, III.3 / 2) Dominant / 3) Six / 4) 2 girls, 1 affected / 5) niece-uncle and grandma-grandson

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Huntington's disease is an autosomal dominant affection.  

It is expressed by heterozygous individuals, meaning that only one copy of the altered gene is enough to express the phenotype.

The mutated gene is the dominant one.

I will answer these questions according to the attached pedigree.

A pedigree is the representation of family history through which it is possible to follow the inheritance pattern of certain traits.

To correctly interpret a pedigree, we need to consider that,

• Squares represent males or men,
• Circles represent females or women.

• Solid figures represent affected individuals,
• Empty figures represent normal individuals.

• Roman numbers indicate generations.

• Individuals can be identified using numbers, genotypes, names, or others.

1. Which members of the family above are afflicted with Huntington's Disease?

• I.1 ⇒ Man of the first generation

• II.2, II.3, II.7 ⇒ Two women and one man of the second generation

• III.3 ⇒ One woman of the third generation.

2. There are no carriers for Huntington's Disease- you either have it or you don't. With this in mind, is Huntington's disease caused by a dominant or recessive trait?

Huntington's disease is caused by a dominant allele. So a single altered gene is enough to express the affection.

3. How many children did individuals l-1 and 1-2 have?

They had six children.

• Two affected girls  ⇒ solid circles ⇒ Individuals II.2 and II.7

• One normal girl ⇒ empty circle ⇒ individual II.6

• Two normal boys ⇒ empty squares ⇒ Individuals II.4 and II.8

• One affected boy ⇒ solid square ⇒ Individual II.3

4. How many girls did Il-1 and Il-2 have? How many have Huntington's Disease?

They had two girls

• One affected girl ⇒ Solid circle ⇒ III.3

• One normal girl ⇒ Empty circle ⇒ III.2

5. How are individuals III-2 and II-4 related?  I-2 and III-5?

• III-2 and II-4 ⇒ II.4 man is the uncle of III.2 girl ⇒ uncle-niece

• I-2 and III-5 ⇒ I.2 woman is the grandmother of III.5 boy ⇒

                                    grandmother-grandson

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