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
17
Q
- What happens when an affected mother breeds with an unaffected father?
A
- she has a fair chance of passing her chromosomes
with the mutated gene to all her children
REGARDLESS of their gender - 50% of her children will be affected
18
Q
- What two components do many disease have?
A
- A genetic component
- An environmental component
EG:
- diseases such as cancer and heart diseases
19
Q
- What can Genetic Counsellors provide clients with?
A
- they can provide information to prospective parents
- these parents are often concerned about a family
history for a specific disease
20
Q
- What do Genetic Counsellors use pedigrees for?
A
- pedigrees help to reveal family histories
- genetic counsellors use these to help couples
determine the odds that their children will have genetic
disorders
21
Q
- What 2 teachings is Genetic Counselling based on?
A
- Mendelian Genetics
- Probability Rules
22
Q
- What is the purpose of Genetic Tests?
A
- they identify carriers of various diseases
- they help to define the odds that the offspring will have
the disorder
23
Q
- What is B-thalassaemia?
A
- Beta Thalassaemia is a blood disorder
- it reduces the production of haemoglobin
- Hemoglobin is an iron-containing protein in red blood
cells - it carries oxygen to cells throughout the body
IN PEOPLE WITH B-THALASSAEMIA:
- low levels of haemoglobin reduce oxygen levels in the
body
24
Q
- What percentage of the Cypriot people are affected by B-thalassaemia?
A
- 16% of the Cypriot Population
- they are heterozygous carriers of the B-Thalassaemia
trait (allele)
25
25. What was introduced in Cyprus in the 1970s?
- a Screening Policy
- this helped to reduce the incidence of B-thalassaemia
NB:
- Iran and other countries have similar screening
policies
26
26. What are the 4 options that the Cypriot Government has available to decrease the percentage of B-thalassaemia?
1. Premarital Screening
(this is because 1 out of 8 members of the Cypriot
Population are carriers)
2. Prenatal Screening
3. Abortion
(provided by the government)
4. In Vitro Fertilisation with a healthy embryo
27
27. Have the screening policies had success in lowering the B-thalassaemia percentage amongst the Cypriot population?
- yes
- the number of children born with this hereditary
disease has decreased from 1 in 158 births
TO almost zero
28
28. What is Prenatal Screening?
- this is the testing for diseases or conditions in a foetus
or embryo
- this is done before the child is born
- it assists in detecting birth defects
29
29. List 2 examples of Birth Defects that Prenatal Screening can detect?
1. CHROMOSOMAL ABNORMALITIES
- EG: Down Syndrome
- this is done through karyotyping
- this is when we examine the structure and the total
number of chromosomes of a child's genetics
2. GENETIC DISORDERS
- this is done through genetic testing
30
30. What are 4 examples of Genetic Disorders?
1. Sickle Cell Anaemia
2. Thalassaemia
3. Cystic Fibrosis
4. Muscular Dystrophy
31
31. List 3 examples of Prenatal (Foetal) testing?
1. Amniocentesis
2. Chronic Villus Sampling (CVS)
3. Non-Invasive Prenatal Diagnosis (NIPD)
32
32. What is an Amniocentesis?
- this is when amniotic fluid is removed and tested
- it does pose the danger of causing an abortion
33
33. What is Chronic Villus Sampling (CVS)?
- this is when a sample of the placenta is removed and
tested
34
34. What is Non-Invasive Prenatal Diagnosis (NIPD)?
- this is a new genetic test
- it is when a sample of the mother's blood is removed
and tested
- this blood contains some foetal cells
35
35. What are all 3 of the Prenatal Screenings (Foetal
Tests) followed by?
- karyotyping of the foetal cells
- genetic testing of the foetal cells
- this can reveal possible abnormalities
36
36. List 2 techniques that allow foetal health to be
assessed visually in utero?
1. Ultrasounds
2. Foetoscopy
37
37. What is one example of a disorder that can be detected by a Newborn Screening Program?
- Phenyketonuria
- this disorder can be detected at birth
- a series of simple tests are routinely performed in
hospitals
38
38. What is Phenyketonuria?
- this is an Autosomal Recessive Disorder
- it affects 1 in every 10 000-15 000 births
- it is when there is an inability to metabolise a specific
amino acid
- this amino acid is Phenylalanine
39
39. Where does the Phenylalanine Amino Acid accumulate?
- it accumulates in the blood
- it accumulates in the urine
40
40. What is a harmful effect of Phenyketonuria?
- mental retardation
41
41. How can Phenyketonuria be treated?
- it can be treated with a low diet of Phenylalanine
- this only works if the disorder is detected early
