Mendelian Inheritance

Question 1

what is the name of the inheritance diagram with squares and circles?

Answer 1

pedigree diagram

Question 2

what gender does the square represent?

Answer 2

Male

Question 3

what gender does the circle represent?

Answer 3

female

Question 4

what does the diamond represent?

Answer 4

a baby with unknown gender

Question 5

Cystic fibrosis

Answer 5

a autosomal recessive condition- thick and sticky mucus
in the UK the risk for anyone of being a carrier is 1 in 25
and the chance of being affected is 1 in 2500
in a recessive condition you usually n
eed a double recessive allele- rr to have the disease
Rr dominant allele masks it

example:
sister and brother- brother is affected by C.F the daughter is 23 and asymptomatic so can say she is unaffected but she is still a carrier as both her parents were.
She now has a 2 in 3 chance of being a carrier as one is we forget the double recessive.

She wants to know her baby’s risk of getting C.F…
Her partner has 1 in 25 chance so you times that by 2 in 3 to get 2 in 75 risk which is her baby’s risk of being affected

Question 6

Achondroplasia

Answer 6

autosomal dominant inheritance. Bone growth disorder- dwarfism

50/ 50 chance of children being affected

A      a  a  Aa   aa

a Aa aa

2 dominant= affected

Question 7

Population risk

Answer 7

very low risk but not 0 as

Question 8

Huntington’s disease

Answer 8

neuro-degenerative disease 
autosomal dominant 
H is the huntington's allele
      h     h
H  Hh   Hh
h   hh   hh

50/50

Question 9

ways to prevent not passing on a disease if you are a carrier?

Answer 9

screening of embryo’s and analysing the DNA for the presence of one or more disease-associated genetic alterations
not having children or adopting

Question 10

Duchenne muscular dystrophy

Answer 10

muscle weakness, fatal in early adult life
x linked disease
males are not affected 
females are 
risk= 1 of a female
son has 1 in 2 chance of being a carrier

Question 11

in autosomal recessive inheritance what is needed for a condition to be developed?

Answer 11

both copies of gene- rr

Question 12

What is a healthy carrier in autosomal recessive?

Answer 12

Rr

they carry the recessive gene but are not showing it

Question 13

If both parents carry faulty gene ie Rr and Rr- what are the chances the children will inherit the condition

Answer 13

1 in 4

Question 14

What does a dominant allele do? Aa

Answer 14

dominant allele masks/ suppresses the expression of another allele

Question 15

autosomal dominant

Answer 15

every generation is affected
each child has 50% chance of inheriting the mutation
both sexes are affected in equal proportion

Question 16

autosomal recessive

Answer 16

generations can be skippied/unaffected
need double recessive to express trait
both sexes affected in equal proportion

Question 17

X linked recessive

Answer 17

males affected more than females as females have two X chromosomes
- males cannot transmit disorders to son as they have to pass on their Y chromosome to the son
daughters of affected male will be carriers and can pass on disease
e.g haemophilia or Duchenne muscular dystrophy.

Question 18

Y- linked inheritance

Answer 18

affects males only

father to son only

Question 19

what does consanguinity mean and how is it represented in a pedigree diagram?

Answer 19

means mating with blood relation

it’s represented by a double horizontal line

Question 20

how to calculate allele frequency if say:-

105 AA 200 Aa 95aa

Answer 20

so 
A= 2x105 + 200 = 410
a= 2x95 + 200= 390 
in total there are 800 
so 390/800= 0.49   410/800= 0.51 
must equal 1 so 0.49 + 0.51 = 1

Question 21

proband in pedigree diagrams

Answer 21

usually the first affected family member who brings a genetic disorder to the attention of the medical professional
arrow is used to point them out in a pedigree