5.7 Tracing your family history

• Biologie
• Middelbare school
• havo, vwo
• Leerjaar 3

When a gene is located on the X-chromosome, we call this a ...

Can a man be a carrier for a sex-linked-gene?

Why do men have a higher chance of expressing a sex-linked-gene in their phenotype?

pedigree

 A pedigree is a visual tool for 

following an inherited characteristic 

through generations of a family.

female - circle

male - square

who is brother/sister of who

who is new to the family

PEDIGREES

black square is male with disease

black circle is female with disease

X-linked dominant? or

X-linked recessive? 

a filled in square or circle means it expresses the characteristics (trait)

usually you cant see who is carrier

both male are affected with no affected female so its X-linked and since male 3 doesnt have its recessive

black circle is female with disease

black square is male with disease

4

what is the genotype of person 4?

person 4 Aa

LET'S PRACTISE 

Could this disease be ...

a. autosomal dominant? 

b. autosomal recessive? 

c. X-linked dominant? 

d. X-linked recessive? 

Yes / No ? Explain your answer. 

Autosomes

Autosomes

'Normal' genes

AA - Aa - aa

Sex chromosomes

Sex-linked genes

XHXH - XHXh - XhXh 

XHY - XhY

LET'S PRACTISE 

Could this disease be ...

a. autosomal dominant? No

b. autosomal recessive? Yes

c. X-linked dominant? No

d. X-linked recessive? Yes

Yes / No ? Explain your answer. 

LET'S PRACTISE!

Answer the exercises to practise how to calculate probabilities & apply your knowledge on mutations. 

LET'S CHECK THE HOMEWORK

Download the answers from SOM &

Discuss the answers with a classmate.