Probabilities in Simple Autosomal Recessive Mode of Inheritance

1. Probabilities based on known carriers in a pedigree.
2. Mendelian ratios for litter sizes 1 to 12.
3. Relative Risk Assessment by Jim Seltzer
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1. Probabilities based on known carriers in a pedigree

(Please note that the numbers are statistical and cannot be used on single combinations - they only state the statistical probability, they do not predict the outcome of a combination)

BOTH PARENTS ARE CARRIERS

Pedigree:

Offspring Parents
sick: 1 out of 4 (25%)
Healthy carrier: 2 out of 4 (50%)
Clear: 1 out of 4 (25%)		 Carrier
Carrier

Genetic combinations:

 
Carrier(Hs)
Carrier(Hs)
HH
Clear
Hs
Carrier
sH
Carrier
ss
sick

 

ONE PARENT IS A CARRIER. THE OTHER PARENT HAS A CARRIER PARENT

Pedigree:

Offspring Parents Grandparents
Sick: 1 out of 8 (12,5%)
Healthy carrier: 4 out of 8 (50%)
Clear: 3 out of 8 (37,5%)		   Carrier
 
Carrier  
 

Genetic combinations:

  Carrier(Hs) Clear(HH)
Carrier(Hs) HH Hs sH ss HH HH sH sH

 

ONE GRANDPARENT ON EACH SIDE IS A CARRIER

Pedigree:

Offspring Parents Grandparents
Sick: 1 out of 16 (6,25%)
Healthy carrier: 6 out of 16 (37,5%)
Clear: 9 out of 16 (56,25%)		    
Carrier
   
Carrier

Genetic combinations:

  Carrier(Hs) Clear(HH)
Clear(HH) HH Hs HH Hs HH HH HH HH
Carrier(Hs) HH Hs sH ss HH HH sH sH

 

ONE PARENT AND ONE GREAT-GRANDPARENT ON EACH SIDE IS A CARRIER

Pedigree:

Offspring Parents Grandparents G-Grand
parents

Sick:
1 out of 16 (6,25%)

Healthy carrier:
8 out of 16 (50,00%)

Clear:
7 out of 16 (43,75%)

      
 
  Carrier
 
Carrier    
 
   
 

Genetic combinations:

  Clear(HH) Clear(HH) Clear(HH) Carrier(Hs)
Carrier(Hs) HH HH sH sH HH HH sH sH HH HH sH sH HH Hs sH ss

 

ONE GRANDPARENT AND ONE GREAT-GRANDPARENT ON EACH SIDE IS A CARRIER

Pedigree:

Offspring Parents Grandparents G-Grand
parents

Sick:
1 out of 32 (3,1%)

Healthy carrier:
10 out of 32 (31,3%)

Clear:
21 out of 32 (65,6%)

      
Carrier
   
 
     
 
Carrier  
 

Genetic combinations:

  Clear(HH) Clear(HH) Clear(HH) Carrier(Hs)
Clear(HH) HH HH HH HH HH HH HH HH HH HH HH HH HH HH Hs Hs
Carrier(Hs) HH HH sH sH HH HH sH sH HH HH sH sH HH Hs sH ss

 

ONE GREAT-GRANDPARENT ON EACH SIDE IS A CARRIER

Pedigree:

Offspring Parents Grandparents G-Grand
parents

Sick:
1 out of 64 (1,56%)

Healthy carrier:
14 out of 64 (21,9%)

Clear:
49 out of 64 (76,6%)

      
 
  Carrier
 
    Carrier
 
   
 

Genetic combinations:

  Clear(HH) Clear(HH) Clear(HH) Carrier(Hs)
Clear(HH) HH HH HH HH HH HH HH HH HH HH HH HH HH HH Hs Hs
Clear(HH) HH HH HH HH HH HH HH HH HH HH HH HH HH HH Hs Hs
Clear(HH) HH HH HH HH HH HH HH HH HH HH HH HH HH HH Hs Hs
Carrier(Hs) HH HH sH sH HH HH sH sH HH HH sH sH HH Hs sH ss

 

ONE GREAT-GREAT-GRANDPARENT ON EACH SIDE IS A CARRIER

Pedigree:

Offspring Parents Grandparents G-Grand
parents		 G-G-Grandparent

Sick:
(0,39%)

Healthy carrier:
(11,7%)

Clear:
(87,9%)

        
 
  Carrier
 
     
 
   
 
       
 
   
 
    Carrier
 
   
 

Genetic combinations:

  Clear(HH) Clear(HH) Clear(HH) Carrier(Hs)
Clear(HH) HH HH HH HH HH HH HH HH HH HH HH HH HH HH Hs Hs
Clear(HH) HH HH HH HH HH HH HH HH HH HH HH HH HH HH Hs Hs
Clear(HH) HH HH HH HH HH HH HH HH HH HH HH HH HH HH Hs Hs
Carrier(Hs) HH HH sH sH HH HH sH sH HH HH sH sH HH Hs sH ss

 

 

2. Mendelian ratios for litter sizes 1 to 12.
(Probabilities of getting sick offspring when both parents are healthy carriers):

Litter size: 1 pup

Healthy pups
Sick pups
Probability
Explaination
1
0
75%
In 3 out of 4 combinations, the pup will be healthy
0
1
25%
In 1 out of 4 combinations, the pup will be affected

 

Litter size: 2 pups

Healthy pups
affected pups
Probability
Explaination
2
0
56.3%
In more than half of the combinations with 2 pups, none of the puppies will be affected.
1
1
37.5%
A bit more often than every third combination with 2 pups, there will be one affected and one healthy pup.
0
2
6.25%
In 1 out of 16 combinations with 2 pups, both pups will be affected

 

Litter size: 3 pups

Healthy pups
affected pups
Probability
Explaination
3
0
42.2%
In almost half of the combinations with 3 pups, none of the puppies will be affected.
2
1
42.2%
In almost half of the combinations with 3 pups, there will be two healthy and one affected pup.
1
2
14.1%
In one out of 7 combinations with 3 pups, one pup will be healthy and two will be affected.
0
3
1.5%
In one out of 67 combinations with 3 pups, all three pups will be affected.

 

Litter size: 4 pups

Healthy pups
affected pups
Probability
Explaination
4
0
31.6%
In one out of three combinations with 4 pups, none of the puppies will be affected.
3
1
42.2%
In more than one out of three combinations with 4 pups, three will be healthy and one will be affected.
2
2
21.1%
In one out of five combinations with 4 pups, there will be two healthy and two affected.
1
3
4.7%
In one out of 21 combinations with 4 pups, one will be healthy and three will be affected.
0
4
0.4%
In one out of 250 combinations with 4 pups, all four will be affected.

 

Litter size: 5 pups

Healthy pups
affected pups
Probability
Explaination
5
0
23.7%
In one out of five combinations with 5 pups, none of the pups will be affected.
4
1
39.5%
In more than one out of three combinations with 5 pups, four will be healthy and one will be affected.
3
2
26.4%
In one out of four combinations with 5 pups, there will be three healthy and two affected.
2
3
8,8%
In one out of 11combinations with 5 pups, there will be two healthy and three affected.
1
4
1.5%
In one out of 67 combinations with 5 pups, there will be one healthy and four affected.
0
5
0.1%
In one out of 1000 combinations with 5 pups,all will be affected.

 

Litter size: 6 pups

Healthy pups
affected pups
Probability
Explaination
6
0
17.8%
In more than 1 out of 6 combinations with 6 pups, all will be healthy.
5
1
35.6%
In more than 1 out of 3 combinations with 6 pups, there will be five healthy and one affected.
4
2
29.7%
In almost 1 out of 3 combinations with 6 pups, four will be healthy and two will be affected.
3
3
13.2%
In 1 out of 8 combinations with 6 pups, three will be healthy and three will be affected.
2
4
3.3%
In 1 out of 30 combinations with 6 pups, two will be healthy and four will be affected.
1
5
0.4%
In 1 out of 250 combinations with 6 pups, one will be healthy and five will be affected.
0
6
0.02%
In 1 out of 5000 combinations with 6 pups, all six will be affected.

 

Litter size: 7 pups

Healthy pups
affected pups
Probability
Explaination
7
0
13.3%
In 1 out of 8 combinations with 7 pups, all will be healthy.
6
1
31.1%
In 1 out of 3 combinations with 7 pups, there will be one affected and six healthy.
5
2
31.1%
In 1 out of 3 combinations with 7 pups, there will be two affected and five healthy.
4
3
17.3%
In 1 out of 6 combinations with 7 pups, there will be three affected and four healthy.
3
4
5.8%
In 1 out of 17 combinations with 7 pups, there will be four affected and three healthy.
2
5
1.2%
In 1 out of 83 combinations with 7 pups, there will be five affected and two healthy.
1
6
0.1%
In 1 out of 1000 combinations with 7 pups, there will be six affected and one healthy.
0
7
0.01%
In 1 out of 10 000 combinations with 7 pups, all will be affected.

 

Litter size: 8 pups

Healthy pups
affected pups
Probability
Explaination
8
0
10.0%
In 1 out of 10 combinations with 8 pups, all will be healthy.
7
1
26.7%
In 1 out of 4 combinations with 8 pups, there will be one affected and seven healthy.
6
2
31.1%
In 1 out of 3 combinations with 8 pups, there will be two affected and six healthy.
5
3
20.8%
In 1 out of 5 combinations with 8 pups, there will be three affected and five healthy.
4
4
8.7%
In 1 out of 11 combinations with 8 pups, there will be four affected and four healthy.
3
5
2.3%
In 1 out of 43 combinations with 8 pups, there will be five affected and three healthy.
2
6
0.4%
In 1 out of 250 combinations with 8 pups, there will be six affected and two healthy.
1
7
0.04%
In 1 out of 2500 combinations with 8 pups, there will be seven affected and one healthy.
0
8
0.002%
In 1 out of 50 000 combinations with 8 pups, all will be affected.

 

Litter size: 9 pups

Healthy pups
affected pups
Probability
Explaination
9
0
7.5%
In 1 out of 13 combinations with 9 pups, all will be healthy.
8
1
22.5%
In more than 1 out of 5 combinations with 9 pups, there will be one affected and eight healthy.
7
2
30.0%
In 1 out of 3 combinations with 9 pups, there will be two affected and seven healthy.
6
3
23.4%
In 1 out of 4 combinations with 9 pups, there will be three affected and six healthy.
5
4
11.7%
In 1 out of 9 combinations with 9 pups, there will be four affected and five healthy.
4
5
3.9%
In 1 out of 25 combinations with 9 pups, there will be five affected and four healthy.
3
6
0.9%
In 1 out of 111 combinations with 9 pups, there will be six affected and three healthy.
2
7
0.1%
In 1 out of 1000 combinations with 9 pups, there will be seven affected and two healthy.
1
8
0.01%
In 1 out of 10 000 combinations with 9 pups, there will be eight affected and one healthy.
0
9
0.0004%
In 1 out of 250 000 combinations with 9 pups, all will be affected.

 

Litter size: 10 pups

Healthy pups
affected pups
Probability
Explaination
10
0
5.6%
In 1 out of 18 combinations with 10 pups, all will be healthy.
9
1
18.8%
In 1 out of 5 combinations with 10 pups, there will be one affected and nine healthy.
8
2
28.2%
In more than 1 out of 4 combinations with 10 pups, there will be two affected and eight healthy.
7
3
25.0%
In 1 out of 4 combinations with 10 pups, there will be three affected and seven healthy.
6
4
14.6%
In 1 out of 7 combinations with 10 pups, there will be four affected and six healthy.
5
5
5.8%
In 1 out of 17 combinations with 10 pups, there will be five affected and five healthy.
4
6
1.6%
In 1 out of 63 combinations with 10 pups, there will be six affected and four healthy.
3
7
0.3%
In 1 out of 333 combinations with 10 pups, there will be seven affected and three healthy.
2
8
0.04%
In 1 out of 2500 combinations with 10 pups, there will be eight affected and two healthy.
1
9
0.003%
In 1 out of 33 333 combinations with 10 pups, there will be nine affected and one healthy.
0
10
0.0001%
In 1 out of 100 000 combinations with 10 pups, all will be affected.

 

Litter size: 11 pups

Healthy pups
affected pups
Probability
Explaination
11
0
4.2%
In 1 out of 24 combinations with 11 pups, all will be healthy.
10
1
15.5%
In more than 1 out of 7 combinations with 11 pups, there will be one affected and ten healthy.
9
2
25.8%
In 1 out of 4 combinations with 11 pups, there will be two affected and nine healthy.
8
3
25.8%
In 1 out of 4 combinations with 11 pups, there will be three affected and eight healthy.
7
4
17.2%
In more than 1 out of 6 combinations with 11 pups, there will be four affected and seven healthy.
6
5
8.0%
In more than 1 out of 12 combinations with 11 pups, there will be five affected and six healthy.
5
6
2.7%
In 1 out of 37 combinations with 11 pups, there will be six affected and five healthy.
4
7
0.6%
In 1 out of 167 combinations with 11 pups, there will be seven affected and four healthy.
3
8
0.1%
In 1 out of 1000 combinations with 11 pups, there will be eight affected and three healthy.
2
9
0.01%
In 1 out of 10 000 combinations with 11 pups, there will be nine affected and two healthy.
1
10
0.0008%
In 1 out of 125 000 combinations with 11 pups, there will be ten affected and one healthy.
0
11
0.00002%
In 1 out of 5 million combinations with 11 pups, all will be affected.

 

Litter size: 12 pups

Healthy pups
affected pups
Probability
Explaination
12
0
3.2%
In 1 out of 31 combinations with 12 pups, all will be healthy.
11
1
12.7%
In 1 out of 8 combinations with 12 pups, there will be one affected and eleven healthy.
10
2
23.2%
In almost 1 out of 4 combinations with 12 pups, there will be two affected and ten healthy.
9
3
25.8%
In 1 out of 4 combinations with 12 pups, there will be three affected and nine healthy.
8
4
19.4%
In 1 out of 5 combinations with 12 pups, there will be four affected and eight healthy.
7
5
10.3%
In 1 out of 10 combinations with 12 pups, there will be five affected and seven healthy.
6
6
4.0%
In 1 out of 25 combinations with 12 pups, there will be six affected and six healthy.
5
7
1.1%
In 1 out of 91 combinations with 12 pups, there will be seven affected and five healthy.
4
8
0.2%
In 1 out of 500 combinations with 12 pups, there will be eight affected and four healthy.
3
9
0.04%
In 1 out of 2500 combinations with 12 pups, there will be nine affected and three healthy.
2
10
0.004%
In 1 out of 25 000 combinations with 12 pups, there will be ten affected and two healthy.
1
11
0.0002%
In 1 out of 500 000 combinations with 12 pups, there will be eleven affected and one healthy.
0
12
0.000006%
In 1 out of 16 666 667 combinations with 12 pups, all will be affected.

Questions or remarks? This page was created by and is maintained by Turid Teigen, Inupiat Alaskan Malamute, Norway.