Basic Genetics

 

Genetic and Morphological Terms

 (developed by Ron Michelotti)

Albinism- a simple recessive mutation where the animal completely lacks melanin

Allele- (see gene)

Anerytherism- a simple recessive mutation where the animal lacks erythrin, or red pigment

Axanthism- a simple recessive mutation where the animal completely lacks yellow and red pigment

Codominant mutation- this mutation is expressed in varying degrees whenever the mutant allele appears in the genotype; it can be intensified if the  offspring receives the mutant alleles from both parents (homozygous condition)

Dihybrid cross- shows the possible genotype of offspring as the result of the pairing of two different genes

Dominant character- the individual need only receive one dominant allele from one parent to be expressed (unlike a simple recessive trait); uppercase letters are often used in writing the genotype

Double Het(erozygous)- the animal is heterozygous for two different traits

F1 (filial 1)- 1st generation from parental generation (usually an original pair from a particular bloodline or wild type) 

F2 (filial 2)- 2nd generation from parental generation; in herpetoculture, these offspring have been selectively bred and are often more desirable in color and/or pattern variations

Gamete-  a sex cell (e.g. egg or sperm) often written in genotypic form when doing genetic crosses

Gene- a specific location (locus) on one of the animal's chromosomes responsible for a particular function (or character in this case); they are made up of a pair of alleles, each coming from the parents of the individual

Genotype- the animal's genetic makeup

Ghost- hypomelanistic and anerytheristic snake

Heterozygous-  refers to a situation where the genotype of a particular gene is dissimilar (e.g. Aa); a heterozygous organism is often referred to as a carrier of a specified gene, which may or may not be expressed depending on the mutation (i.e. dominant, recessive, codominant)

Homozygous- refers to a situation where the genotype (or pair of alleles) of a particular gene locus is (are) identical (e.g. AA, aa)

Hypomelanistic- a codominant mutation (in boa constrictors) where the animal lacks varying degrees of melanin, or black pigment

Phenotype- refers to the character actually expressed

Salmon Snow- hypomelanistic, anerytheristic, and albino snake

Simple recessive mutaiton- a charater controlled by only one gene and is expressed when the offspring receives the mutant alleles from both parents; lowercase letters are often used in writing the genotype

Snow- anerytheristic and albino snake

Sunglow- hypomelanistic and albino snake

Triple Het(erozygous)- the animal is heterozygous for three different mutations

 

A Simple Monohybrid Cross using a Punnett Square

Question: What are the possible offspring as the result of the pairing of a male albino boa with a female boa heterozygous for albinism?

Genotype of male:       aa
Genotype of female:    Aa

Albino (aa) x Het for Albino (Aa)

Possible Gametes a a
A Aa Aa
a aa aa

Answer: Approximately 50% of the offspring will be albino (aa) and the other 50% heterozygous for albinism (Aa).  Please notice, the het for albinos are carriers because they have the albino gene from one of their parents.

 

Sample Dihybrid Crosses

KEY of Alleles

S- codominat allele for "salmon" hypomelanism
s- normal allele for melanin production

A- normal allele for melanin production
a- recessive allele for albinism

N- normal allele for erythrin production (red pigment)
n- recessive allele for anerytherism

 

How to get Salmon Sunglow Boas

Albino (ssaa) x  Double Het for Sunglow (SsAa)

Possible Gene Pairings (Gametes)

sa

SA

SsAa

Sa

Ssaa

sA

ssAa

sa

ssaa

 

Genotypic Ratio of Possible Offspring  

Genotype

Phenotypic Ratio of Possible Offspring  

Phenotype

Probability

1

SsAa

Salmon and het for Albino

1

Salmon (double het for Sunglow)

25%

1

Ssaa

Salmon and Albino

1

Salmon Sunglow

25%

1

ssAa

Normal and het for Albino

1

Normal (het for Albino)

25%

1

ssaa

Albino

1

Albino

25%

 

How to get Super Salmon Sunglow Boas and Salmon Sunglows Boas

Double Het for Sunglow (SsAa) x  Double Het for Sunglow (SsAa)

Possible Gene Pairings (Gametes)

SA

Sa

sA

sa

SA

SSAA

SSAa

SsAA

SsAa

Sa

SSAa

SSaa

SsAa

Ssaa

sA

SsAA

SsAa

ssAA

SsAa

sa

SsAa

Ssaa

ssAa

ssaa

 

Genotypic Ratio of Possible Offspring  

Genotype

Phenotypic Ratio of Possible Offspring  

Phenotype

Probability

1

SSaa

Super Salmon and Albino

3

Salmon/Super Salmon Sunglow

6.25%

2

Ssaa

Salmon and Albino

12.5%

1

SSAA

Super Salmon

9

Salmon/Super Salmon (66.7% Possible Doulble het for Sunglow)

6.25%

2

SSAa

Super Salmon and het for albino

12.5%

2

SsAA

Salmon

12.5%

4 SsAa Salmon and het for Albino 25%

1

ssAA

Normal

3

Normal (66.7% Possible het for Albino)

18.8%

2 ssAa Normal and het for Albino 12.5%

1

ssaa

Albino

1

Albino

6.25%

 

How to get Ghost Boas

Ghost (Ssnn) x  Het for Anery (ssNn)

Possible Gene Pairings (Gametes)

Sn

Sn

sn

sn

sN

SsNn

SsNn

ssNn

ssNn

sn

Ssnn

Ssnn

ssnn

ssnn

 

Genotypic Ratio of Possible Offspring  

Genotype

Phenotypic Ratio of Possible Offspring  

Phenotype

Probability

1

SsNn

Salmon and het for Anery

1

Salmon (double het for Ghost)

25%

1

Ssnn

Salmon and Anery

1

Salmon Ghost (Co-dominant Ghost)

25%

1

ssNn

Normal and het for Anery

1

Normal (het for Anery)

25%

1

ssnn

Anery

1

Anery

25%

 

How to get Super Ghosts

Ghost (Ssnn) x  Double Het for Ghost (SsNn)

Possible Gene Pairings (Gametes)

Sn

sn

SN

SSNn

SsNn

Sn

SSnn

Ssnn

sN

SsNn

ssNn

sn

Ssnn

ssnn

 

Genotypic Ratio of Possible Offspring  

Genotype

Phenotypic Ratio of Possible Offspring  

Phenotype

Probability

1

SSnn

Super Salmon and Anery

3

Salmon/Super Salmon Ghost (66.7% Possible Co-dominant Ghost)

12.5%

2

Ssnn

Salmon and Anery

25%

1

SSNn

Super Salmon and het for Anery

3

Salmon/Super Salmon (het for Ghost)

12.5%

2

SsNn

Salmon and het for Anery

25%

1

ssnn

Anery

1

Anery

12.5%

1 ssNn

Normal and het for Anery

1

Normal (het for Anery)

12.5%

 

What to expect of actual litters?


This photo is a litter produced by Boaman Mike resulting from the pairing of a male Double Het for Ghost (SsNn) and female anerytheristic (ssnn).  Notice, there are 8 co-dominant ghosts, 7 anerys, 5 hets for anery, and no double hets for ghost.  Remember, Punnett squares only give you the probable outcomes (listed below) as a result of various pairings.

Genotype

Phenotypic Ratio of Possible Offspring  

Actual Phenotypic Ratio of Offspring  

Phenotype

SsNn

1

0

Salmon (double het for Ghost)

Ssnn

1

8

Salmon Ghost (Co-dominant Ghost)

ssNn

1

5

Normal (het for Anery)

ssnn

1

7

Anery

 

Triple Het Breeding

Triple Het for Salmon Snow (SsNnAa) x  Triple Het for Salmon Snow (SsNnAa)

Possible Gene Pairings (Gametes) SNA SNa SnA Sna sNA sNa snA sna
SNA SSNNAA SSNNAa SSNnAA SSNnAa SsNNAA SsNNAa SsNnAA SaNnAa
SNa SSNNAa SSNNaa SSNnAa SSNnaa SsNNAa SsNNaa SsNnAa SsNnaa
SnA SSNnAA SSNnAa SSnnAA SSnnAa SsNnAA SsNnAa SsnnAA SsnnAa
Sna SSNnAa SSNnaa SSnnAa SSnnaa SsNnAa SsNnaa SsnnAa Ssnnaa
sNA SsNNAA SsNNAa SsNnAA SsNnAa ssNNAA ssNNAa ssNnAA ssNnAa
sNa SsNNAa SsNNaa SsNnAa SsNnaa ssNNAa ssNNaa ssNnAa ssNnaa
snA SsNnAA SsNnAa SsnnAA SsnnAa ssNnAA ssNnAa ssnnAA ssnnAa
sna SsNnAa SsNnaa SsnnAa Ssnnaa ssNnAa ssNnaa ssnnAa ssnnaa


Genotypic Ratio of Possible Offspring  

Genotype

Phenotypic Ratio of Possible Offspring  

Phenotype

Probability

1 SSnnaa Super Salmon, Anery, and Albino 3 Salmon/Super Salmon Snow 1.6%
2 Ssnnaa Salmon, Anery, and Albino 3.1%
2 SSNnaa Super Salmon, het for Anery, and Albino 9 Sunglow/Super Sunglow (66.7% Possible het for Salmon Snow) 3.1%
1 SSNNaa Super Salmon and Albino 1.6%
4 SsNnaa Salmon, het for Anery, and Albino 6.3%
2 SsNNaa Salmon and Albino 3.1%
1 ssnnaa Anery and Albino 1 Snow 1.6%
2 SSnnAa Super Salmon, Anery, and het for Albino 9 Ghost/Super Ghost (66.7% Possible het for Salmon Snow) 3.1%
1 SSnnAA Super Salmon and Anery 1.6%
4 SsnnAa Salmon, Anery, and het for Albino 6.3%
2 SsnnAA Salmon and Anery 3.1%
4 SSNnAa Super Salmon, het for Anery, and het for Albino 27 Salmon/Super Salmon (44.4% Possible het for Salmon Snow, 22.2% het for Sunglow, and  22.2% het for Ghost) or (66.7% Possible het for Anery and Albino) 6.3%
8 SsNnAa Salmon, het for Anery, and het for Albino 12.5%
2 SSNNAa Super Salmon and het for Albino 3.1%
2 SSNnAA Super Salmon and het for Anery 3.1%
1 SSNNAA Super Salmon 1.6%
4 SsNNAa Salmon and het for Albino 6.3%
4 SsNnAA Salmon and het for Anery 6.3%
2 SsNNAA Salmon 3.1%
2 ssNnaa Het for Anery and Albino 3 Albino (66.7% Possible het for Snow) 3.1%
1 ssNNaa Albino 1.6%
2 ssnnAa Anery and het for Albino 3 Anery (66.7% Possible het for Snow) 3.1%
1 ssnnAA Anery 1.6%
4 ssNnAa Het for Anery and het for Albino 9 Normal (44.4% Possible Double het for Snow, 22.2% het for Albino, and 22.2% het for Anery) or (66.7% Possible het for Anery and Albino) 6.3%
2 ssNNAa Het for Albino 3.1%
2 ssNnAA Het for Anery 3.1%
1 ssNNAA Normal 1.6%

 

 

 

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