typical and atypical mendelian inheritance

Question 1

a vertical pattern of inheritance would suggest?

Answer 1

autosomal dominant condition

Question 2

why would you look for male-to-male transmission?

Answer 2

to establish if it is the X chromosome that is causing the issue

Question 3

what is incomplete penetrance

Answer 3

inheriting a gene may not make it certain that you will be affected by a condition, only more likely

Question 4

what is complete penetrance

Answer 4

If you inherit the mutation and get the disorder always it is complete. Achondroplasia has complete penetrance

Question 5

what is gonadal mosaicism

Answer 5

where more than one set of genetic information is found specifically within the gamete cells

Question 6

what pattern is seen in autosomal recessive inheritance

Answer 6

horizontal

Question 7

give examples of autosomal recessive conditions

Answer 7

CF, PKU, congenital adrenal hyperplasia, spinal muscular atrophy

Question 8

what risk do offspring of an affected adult have of developing an autosomal dominant condition ?

Answer 8

50%

Question 9

what risk do offspring of an affected adult have of developing an autosomal recessive condition

Answer 9

very low (would need to have two parents with the faulty gene)

Question 10

what major feature does X-linked recessive inheritance show

Answer 10

Knight’s move pattern

Can pass through unaffected females and onto a male.

Question 11

what is an obligate carrier?

Answer 11

those who can be calculated to definitely be a carrier of the genetic condition

Question 12

what percentage of a female carrier of an x-linked recessive condition son’s will be affected by the condition?

Answer 12

50%

Question 13

what percentage of a female carrier of an x-linked recessive condition daughter’s will be carriers for the condition?

Answer 13

50%

Question 14

what proportions of male offspring of a male heterozygote for an X-linked recessive condition will be affected

Answer 14

none

Question 15

what proportions of daughter of a male heterozygote for an X-linked recessive condition will be carriers

Answer 15

all

Question 16

give some examples of an X-linked recessive condition

Answer 16

• Red-green colour blindness
• Haemophilia A and B
• Duchenne muscular dystrophy

Question 17

what pattern do you see in x-linked dominant conditions?

Answer 17

female to female, and female to male but no male to male

vertical pattern

Question 18

give some examples of x-linked dominant condition

Answer 18

o Vitamin D resistant rickets
o Incontintentia pigmenti (has male lethality)
o Rett syndrome (male lethality – usually)

Question 19

what proportion of daughters will be affected in male to female transmission in x-linked dominant conditions

Answer 19

all

Question 20

what is genetic anticipation

give examples

Answer 20

genetic condition in which there is increasing severity and earlier age of onset with successive generations
Huntington’s disease, myotonic dystrophy and Fragile X syndrome

Question 21

what is pseudo-dominant inheritance

Give an example

Answer 21

this is where there is a very high carrier frequency for a condition so on family tress it looks like autosomal dominant
Gilbert’s syndrome