7. SEX CHROMOSOME LINKED DISORDERS Flashcards
1
Q
- What causes Sex Chromosome Linked Disorders?
A
- they are caused by mutations on the alleles
- these alleles are found on the sex chromosomes
(the X and the Y chromosomes)
2
Q
- What can be said about the genes on the Y Chromosome?
A
- the Y chromosome has very few genes
- this means that there are very few Y-Linked disorders
3
Q
- What are most Sex Chromosome Linked Disorders a
result of?
A
- mutations on the genes on the X chromosome
- these are known as X linked disorders
4
Q
- What are the 2 types of X-linked disorders?
A
- X-Linked Dominant
- X-Linked Recessive
5
Q
- Which kind of X-linked disorder is more common?
A
- X-linked recessive disorders are much more common
6
Q
- In which gender are X-linked recessive disorders much more common?
A
- these kinds of disorders are much more common in
men than in women - this is due to the absence of the allele on the Y
chromosome - this is because the X and the Y chromosome are non-
homologous
7
Q
- What are X-linked Recessive Disorders?
A
- this is a disorder on the X chromosome
- the recessive, mutant allele is present on the one X
chromosome
IN MALES:
- there is an absence of the normal allele on the Y
chromosome
8
Q
- What happens to the offspring if the mother is a carrier of an X-linked recessive disorder?
A
- 50% of her sons will be affected
9
Q
- Are females often affected by X-linked recessive disorders?
A
- no
- they are rarely affected
- this is because women have another X chromosome
- this X chromosome has the normal allele on it
- this dominant, normal allele will ensure that the
disorder does not appear in the phenotype - women will be carriers of the recessive disorder
10
Q
- What are 3 examples of X-Linked Recessive Disorders?
A
- Haemophilia
- Colour Blindness
- Duchenne Muscular Dystrophy
11
Q
- Fill in descriptions for the following labels related to X-Linked Recessive Disorders.
A
- Normal Woman
(Healthy Female) - Affected Woman
(Woman with the disease) - Normal Male
- Male with the disease
NB:
- there can be no male carriers of this kind of disease
- a women with a XA Xa genotype is a carrier of the
disease
12
Q
- What are 4 characteristics of X-Linked Dominant Disorders?
A
- They are less common than X-linked recessive
disorders - They are extremely rare
- They are usually fatal
- The males are not more affected than the females
13
Q
- Where is the mutant allele found in X-Linked Dominant Disorders?
A
- the mutant allele is dominant
- it is written with a capital letter
- it is found on the X-chromosome
14
Q
- What are 2 examples of X-Linked Dominant Disorders?
A
- Vitamin D Resistant Rickets
(Hypophosphataemic Rickets) - Alport Syndrome
15
Q
- Provide descriptions for the following labels related to X-Linked Dominant Disorders.
A
- Affected Females
- Normal Female
- Affected Male
- Normal Male
16
Q
- What happens in an affected father breeds with an unaffected mother?
A
- the chromosomes with the mutant genes from the
affected father will be inherited by all his daughters - all the daughters will be affected
- none of his sons will be affected