autosomal_recessive_flashcards

Question 1

In autosomal recessive inheritance, who is affected?

Answer 1

Only homozygotes are affected

Question 2

Are males and females equally likely to be affected in autosomal recessive inheritance?

Answer 2

Yes, males and females are equally likely to be affected

Question 3

Is autosomal recessive inheritance manifest in every generation?

Answer 3

No, it may ‘skip a generation’

Question 4

What is the chance of having an affected (homozygote) child if both parents are heterozygotes?

Answer 4

25%

Question 5

What is the chance of having a carrier (heterozygote) child if both parents are heterozygotes?

Answer 5

50%

Question 6

What is the chance of having an unaffected (genotypical) child if both parents are heterozygotes?

Answer 6

25%

Question 7

What is the outcome for children if one parent is affected (homozygote) and the other is unaffected (not a carrier)?

Answer 7

All the children will be carriers

Question 8

What type of disorders are often autosomal recessive?

Answer 8

Often metabolic in nature

Question 9

How do autosomal recessive disorders generally compare in severity to autosomal dominant conditions?

Answer 9

Generally more life-threatening compared to autosomal dominant conditions

Question 10

summarise Autosomal recessive

Answer 10

Autosomal recessive

In autosomal recessive inheritance
only homozygotes are affected
males and females are equally likely to be affected
not manifest in every generation - may ‘skip a generation’

If two heterozygote parents
25% chance of having an affected (homozygote) child
50% chance of having a carrier (heterozygote) child
25% chance of having an unaffected (i.e. genotypical) child

If one affected parent (i.e. homozygote for gene) and one unaffected (i.e. not a carrier or affected)
all the children will be carriers

Autosomal recessive disorders are often metabolic in nature and are generally more life-threatening compared to autosomal dominant conditions

Question 11

A male and female couple attends genetic counselling due to a member of the family being diagnosed with sickle cell anaemia, an autosomal recessive condition. They are both found to be carriers of sickle cell anaemia. The woman is currently 13 weeks pregnant.

What is the probability that their child will be a carrier of sickle cell anaemia?

0%
25%
50%
75%
100%

Answer 11

For autosomal recessive conditions, if both parents are carriers (heterozygote) there is a 50% chance of having a carrier (heterozygote) child
Important for meLess important
This question is testing calculations on the probability of inheritance for sickle cell anaemia. A punnet square could be useful in answering the question. As both parents are carriers of sickle cell anaemia, there is a 50% chance of the child also being a carrier.

0% is incorrect. As at least one of the parents is a carrier of sickle cell anaemia, there is a probability of >0% that the child will be a carrier of the condition.

25% is incorrect. When reviewing the punnet square for this autosomal recessive condition, it can be seen that there is a 25% probability of having the condition or being unaffected, but there is a 50% probability of being a carrier.

75% is incorrect - as described above, the probability of being a carrier is 50%.

100% is not correct. It is not possible to have a 100% probability of being a carrier of an autosomal recessive condition.