The Probability of Inheritance
One of the easiest ways to calculate the mathematical probability of inheriting a specific trait was invented by an early 20th century English geneticist named Reginald Punnett. His technique employs what we now call a Punnett Square. It's a simple graphical way of discovering all of the potential combinations of genotypes that can occur in offspring, given the genotypes of the sire and dam. It also shows us the odds of each of the offspring genotypes occurring withing the pairing.
Setting up and using a Punnett Square is quite simple once you understand how it works. You can find the basic outlines that will help guide you in figuring out what to expect from each pairing on our Punnett Square page located here Punnett Square.
An offspring's genotype is the result of the combination of genes in the sex cells or gametes (sperm and ova) that came together in its conception. One cell comes from each parent. Each of the two Punnett square boxes in which the parent genes for a trait are placed (across the top or on the left side) actually represents one of the two possible genotypes for a parent. Which of the two parental copies of a gene is inherited depends on which trait cell is inherited, it's a matter of chance. By placing each of the two copies in its own box shows the chances of each trait being inherited by the offspring.
Basic Genetic Terminology
With all of the new morphs and designer morphs coming on the scene every year, a basic understanding of genetics is becoming more important with each passing combo. Below is a list of basic genetic terms that will help you in figuring out some of the more complex genetic issues that we as breeders can be faced with in our hobby.
DNA – deoxyribonucleic acid. The molecule whose structure forms the genetic code.
Chromosome – Each cell in every living thing has a nucleus. Much of the nucleus is made up of a constant number of paired chromosomes. Each chromosome is a single, long strand of DNA in a protein matrix. The strand of DNA contains many genes.
Gene – the units of DNA that are transmitted from one generation to the next in the sperm and egg cells. Each gene codes for a specific enzyme. Each enzyme catalyses one step in the biochemical pathway that determines an individual’s phenotype.
Allele – one of two or more alternative forms a gene may take. A homozygous wild type allele, together with wild type alleles at all other loci, produces a normal individual. A changed, or mutant, allele at one locus can block or divert a biochemical pathway to produce a phenotype that is different from the normal.
Locus (plural = loci) – the location on a chromosome where a specific gene resides. Think of it as a street address.
Genotype – the genetic make up of a plant or animal. The identity of an allele or alleles that a single individual has at one or more specified loci.
Phenotype – the physical appearance of the animal as dictated by the genes it has inherited and the influences of the environment.
Heterozygous (100% Het.) – having two different alleles at a given locus.
Homozygous (Homo) – having two identical alleles at a given locus.
Wild Type (Normal) – the phenotype most commonly seen in wild caught individuals. The allele at each locus that produces the wild type phenotype.
Recessive – a mutant allele that changes the phenotype only when in the homozygous. When heterozygous, the individual looks normal.
Codominant – a mutant allele that changes the phenotype when either homozygous or heterozygous. A heterozygous individual does not look like a homozygous individual, and neither does it look like a normal.
Dominant – a mutant allele that changes the phenotype when either homozygous or heterozygous. A heterozygous individual looks like a homozygous individual.
Super Form (Super) – having two codominant alleles at a given locus. This is the homozygous form of a codominant mutant allele.
Double Heterozygous – heterozygous at two gene loci.
Triple Heterozygous – heterozygous at three gene loci.
P generation – two unlike individuals that begin a genetics experiment, or breeding program.
F1 generation – first filial generation. The offspring of the P generation. An F1 is a single member of the F1 generation.
F2 generation – second filial generation. The offspring of two F1s.
F3 generation – third filial generation. The offspring of two F2s.
DNA – deoxyribonucleic acid. The molecule whose structure forms the genetic code.
Chromosome – Each cell in every living thing has a nucleus. Much of the nucleus is made up of a constant number of paired chromosomes. Each chromosome is a single, long strand of DNA in a protein matrix. The strand of DNA contains many genes.
Gene – the units of DNA that are transmitted from one generation to the next in the sperm and egg cells. Each gene codes for a specific enzyme. Each enzyme catalyses one step in the biochemical pathway that determines an individual’s phenotype.
Allele – one of two or more alternative forms a gene may take. A homozygous wild type allele, together with wild type alleles at all other loci, produces a normal individual. A changed, or mutant, allele at one locus can block or divert a biochemical pathway to produce a phenotype that is different from the normal.
Locus (plural = loci) – the location on a chromosome where a specific gene resides. Think of it as a street address.
Genotype – the genetic make up of a plant or animal. The identity of an allele or alleles that a single individual has at one or more specified loci.
Phenotype – the physical appearance of the animal as dictated by the genes it has inherited and the influences of the environment.
Heterozygous (100% Het.) – having two different alleles at a given locus.
Homozygous (Homo) – having two identical alleles at a given locus.
Wild Type (Normal) – the phenotype most commonly seen in wild caught individuals. The allele at each locus that produces the wild type phenotype.
Recessive – a mutant allele that changes the phenotype only when in the homozygous. When heterozygous, the individual looks normal.
Codominant – a mutant allele that changes the phenotype when either homozygous or heterozygous. A heterozygous individual does not look like a homozygous individual, and neither does it look like a normal.
Dominant – a mutant allele that changes the phenotype when either homozygous or heterozygous. A heterozygous individual looks like a homozygous individual.
Super Form (Super) – having two codominant alleles at a given locus. This is the homozygous form of a codominant mutant allele.
Double Heterozygous – heterozygous at two gene loci.
Triple Heterozygous – heterozygous at three gene loci.
P generation – two unlike individuals that begin a genetics experiment, or breeding program.
F1 generation – first filial generation. The offspring of the P generation. An F1 is a single member of the F1 generation.
F2 generation – second filial generation. The offspring of two F1s.
F3 generation – third filial generation. The offspring of two F2s.
Additional Genetic Terminology
Albino - Having the absent or deficient melanin. Widely used term for Amelanistic.
Amelanistic - Having no melanin.
Anerythristic - Having no red color.
Axanthic - Having no yellow color.
Hypomelanistic - An animal having less black and/or brown color than a wild-type.
Leucistic - A pure white animal with dark eyes.
Melanin- Black or brown skin pigments.
Melanistic - Abnormally dark, especially due to an increase of melanin.
Mutation - An abnormal gene that under certain circumstances can cause an animal to be born with an appearance other than wild-type.
Normal - An animal with no mutated genes - "wild type" in appearance.
Tyrosinase - An enzyme required for synthesizing melanin.
Tyrosinase Negative - An albino whose cells lack tyrosinase, producing a white and yellow/orange animal with pink eyes. A separate albino mutation from tyrosinase-positive. Also called T- .
Tyrosinase Positive - An albino not able to synthesize melanin, but capable of synthesizing tyrosinase, which results in lavender-brown skin color. Also referred to as T+.
Xanthic - Increased yellow pigmentation, also known as Tyrosinase-negative (T-).
Amelanistic - Having no melanin.
Anerythristic - Having no red color.
Axanthic - Having no yellow color.
Hypomelanistic - An animal having less black and/or brown color than a wild-type.
Leucistic - A pure white animal with dark eyes.
Melanin- Black or brown skin pigments.
Melanistic - Abnormally dark, especially due to an increase of melanin.
Mutation - An abnormal gene that under certain circumstances can cause an animal to be born with an appearance other than wild-type.
Normal - An animal with no mutated genes - "wild type" in appearance.
Tyrosinase - An enzyme required for synthesizing melanin.
Tyrosinase Negative - An albino whose cells lack tyrosinase, producing a white and yellow/orange animal with pink eyes. A separate albino mutation from tyrosinase-positive. Also called T- .
Tyrosinase Positive - An albino not able to synthesize melanin, but capable of synthesizing tyrosinase, which results in lavender-brown skin color. Also referred to as T+.
Xanthic - Increased yellow pigmentation, also known as Tyrosinase-negative (T-).
Reproductive Terminology
Clutch - The number of eggs laid; egg production and laying. (1. The females of some species clutch several times a year. 2. The average clutch size of adult green iguanas is 50-70 eggs.)
Clutch-mate - Individuals who hatched from the same clutch of eggs.
Co-housing - Housing males and females together.
Cycle, Cycling - The recurring reproductive phase, triggered by hormonal changes triggered by environmental cues. May occur on an annual basis, or a more or less frequent basis.
Estradiol - The estrogen hormon primarily responsible for stimulating yolk synthesis in females.
Fertilization - When a sperm from a male penetrates the ova of a female. In oviparous species, fertilization occurs when the sperm meet the ova as they pass through the oviduct, a passage which also layers the outside of the egg with calcium to form a shell.
Follicle - 1. A small bodily cavity or sac; any small spherical group of cells containing a cavity. pl. follicles. 2. small egg-containing sacks found in the female ovary. In fertile human females, one follicle will become dominant and release a mature egg (ovulate) during every cycle. In oviparous reptile species, several mature eggs will be produced, depending on the species and the individual.
Follicular Vitellogenesis - The development of the yolk in the eggs.
In Vitro - Occurring, or made to occur, outside of a living organism or natural setting (i.e, "test tube babies" are when the egg and sperm have been combined and fertilization occurs in the lab and then implanted into the mother or surrogate).
In Vivo - Occurring, or made to occur, within a living organism or natural setting.
Intromission - The act of copulation, during which the male transfers his sperm into the female. .
Nest - The burrow or pallet dug by the female in which to deposit her eggs.
Oocyte - An egg before maturation (oogenesis).
Oogenesis - The formation and maturation of an egg.
Ova - Eggs. Singular ovum. The mature ova are 10-100 times the size of inactive (pre-vitellogenic) ova. An ovum technically becomes an egg once the albumin and shell are added as they pass through the oviduct into to coelomic cavity.
Ovary - The female gonad, producing eggs and female hormones. The ovary varies in appearance and size depending on the stage of oogenesis. An inactive ovary may appear as a small smear of caviar-looking substance, while an active ovary looks like a mass of white spheres (the developing eggs) held together by transparent membranes laced with blood vessels.
Ovarian Ducts - Var. oviduct. Secrete albumin as well as shelling the eggs.
Ovariectomy - Surgical removal of one or both ovaries.
Ovariosalpingectomy - Surgical removal of the ovary and uterine tube (oviduct).
Oviparous - Egg-laying. (Anoles are oviparous.)
Ovoviviparous - Retains unshelled eggs until ready to hatch; young appear as if by viviparity. (Some skink species are ovovivparous.)
Oviposition - The laying of eggs.
Ovipositor - The hollow tube through which some insects (such as crickets) and chelicerata, lay their eggs. In bees and wasps, this has been modified into the stinger.
Oviposit - To lay or discharge eggs, especially as applied to organisms with a specialized egg-laying structure, such as an ovipositor.
Progesterone - An estrogen antagonist, this steroid hormone produced in the ovary. In uterine mammals, it prepares the uterine lining for the implantation of a fertilized egg.
Prostaglandins - Named for the prostrate gland where these hormone-like chemicals were first discovered, prostaglandins play a varied role in both males and females.
Resorbtion - Some female animals can resorb fully developed eggs. What causes resorbtion in female reptiles is not known, so there is no known way to trigger nor prevent it.
Shell Calcification - The eggs of oviparous reptile are shelled as they pass through the oviducts on their way to the coelomic cavity, which occurs several days prior to laying. The amount of calcification (thickness, rigidity) varies from species to species. The amount of shelling can be adversely affected due to metabolic bone disease caused by pre-exisiting dietary or environmental deficiencies, or gestational/gravidity-induced MBD when gravid females have not received supplemental calcium to prepare them for the increased calcium demands on their bodies to produce eggs and shells.
Slug - An infertile egg.
Vitellogenesis - The development of the egg yolk in the follicles, started when estrogen stimulates the liver to start converting lipids from the body's fat stores, creating vitellogenin. During this time, the liver is enlarged and yellowish-looking.
Vitellogenic Activity - The development and deposition of yolk.
Vitellogenin - A protein, synthesized in the liver after estogen stimulation, that is the precursor to several yolk proteins. The maturing follicles absorb vitellogenin from the bloodstream.
Viviparous - Live-bearing. (Many viperid species are viviparous.)
Yolk Deposition - The deposit of yolk into the ova.
Yolk Synthesis - The development of yolk, initially started in the liver, complete in the ova.
Clutch-mate - Individuals who hatched from the same clutch of eggs.
Co-housing - Housing males and females together.
Cycle, Cycling - The recurring reproductive phase, triggered by hormonal changes triggered by environmental cues. May occur on an annual basis, or a more or less frequent basis.
Estradiol - The estrogen hormon primarily responsible for stimulating yolk synthesis in females.
Fertilization - When a sperm from a male penetrates the ova of a female. In oviparous species, fertilization occurs when the sperm meet the ova as they pass through the oviduct, a passage which also layers the outside of the egg with calcium to form a shell.
Follicle - 1. A small bodily cavity or sac; any small spherical group of cells containing a cavity. pl. follicles. 2. small egg-containing sacks found in the female ovary. In fertile human females, one follicle will become dominant and release a mature egg (ovulate) during every cycle. In oviparous reptile species, several mature eggs will be produced, depending on the species and the individual.
Follicular Vitellogenesis - The development of the yolk in the eggs.
In Vitro - Occurring, or made to occur, outside of a living organism or natural setting (i.e, "test tube babies" are when the egg and sperm have been combined and fertilization occurs in the lab and then implanted into the mother or surrogate).
In Vivo - Occurring, or made to occur, within a living organism or natural setting.
Intromission - The act of copulation, during which the male transfers his sperm into the female. .
Nest - The burrow or pallet dug by the female in which to deposit her eggs.
Oocyte - An egg before maturation (oogenesis).
Oogenesis - The formation and maturation of an egg.
Ova - Eggs. Singular ovum. The mature ova are 10-100 times the size of inactive (pre-vitellogenic) ova. An ovum technically becomes an egg once the albumin and shell are added as they pass through the oviduct into to coelomic cavity.
Ovary - The female gonad, producing eggs and female hormones. The ovary varies in appearance and size depending on the stage of oogenesis. An inactive ovary may appear as a small smear of caviar-looking substance, while an active ovary looks like a mass of white spheres (the developing eggs) held together by transparent membranes laced with blood vessels.
Ovarian Ducts - Var. oviduct. Secrete albumin as well as shelling the eggs.
Ovariectomy - Surgical removal of one or both ovaries.
Ovariosalpingectomy - Surgical removal of the ovary and uterine tube (oviduct).
Oviparous - Egg-laying. (Anoles are oviparous.)
Ovoviviparous - Retains unshelled eggs until ready to hatch; young appear as if by viviparity. (Some skink species are ovovivparous.)
Oviposition - The laying of eggs.
Ovipositor - The hollow tube through which some insects (such as crickets) and chelicerata, lay their eggs. In bees and wasps, this has been modified into the stinger.
Oviposit - To lay or discharge eggs, especially as applied to organisms with a specialized egg-laying structure, such as an ovipositor.
Progesterone - An estrogen antagonist, this steroid hormone produced in the ovary. In uterine mammals, it prepares the uterine lining for the implantation of a fertilized egg.
Prostaglandins - Named for the prostrate gland where these hormone-like chemicals were first discovered, prostaglandins play a varied role in both males and females.
Resorbtion - Some female animals can resorb fully developed eggs. What causes resorbtion in female reptiles is not known, so there is no known way to trigger nor prevent it.
Shell Calcification - The eggs of oviparous reptile are shelled as they pass through the oviducts on their way to the coelomic cavity, which occurs several days prior to laying. The amount of calcification (thickness, rigidity) varies from species to species. The amount of shelling can be adversely affected due to metabolic bone disease caused by pre-exisiting dietary or environmental deficiencies, or gestational/gravidity-induced MBD when gravid females have not received supplemental calcium to prepare them for the increased calcium demands on their bodies to produce eggs and shells.
Slug - An infertile egg.
Vitellogenesis - The development of the egg yolk in the follicles, started when estrogen stimulates the liver to start converting lipids from the body's fat stores, creating vitellogenin. During this time, the liver is enlarged and yellowish-looking.
Vitellogenic Activity - The development and deposition of yolk.
Vitellogenin - A protein, synthesized in the liver after estogen stimulation, that is the precursor to several yolk proteins. The maturing follicles absorb vitellogenin from the bloodstream.
Viviparous - Live-bearing. (Many viperid species are viviparous.)
Yolk Deposition - The deposit of yolk into the ova.
Yolk Synthesis - The development of yolk, initially started in the liver, complete in the ova.
