Animals inherit far more than their looks. Along with fur color and body size, many are born knowing which way to fly in autumn or which shapes to fear. Few of these traits come from a single gene like the textbook pea-plant examples. Most are the combined work of many genes, nudged by where and how the animal grows up.1chowhealth.org. Genetics
How Animals Pass Traits to Their Young
A gene is a stretch of DNA, part of the instruction code every animal gets half from its mother and half from its father. The simple rules most people learn in school come from Gregor Mendel’s pea plants, where one pair of genes decides one trait.2Study.com. 5 Traits That Are Inherited in Animals Animals rarely work that way. Size, temperament, growth rate, longevity and disease resistance are all shaped by many genes that each contribute a little.3chowhealth.org. Genetics
Some traits do fall into clear categories, like whether a deer is black or brown. Traits controlled by many genes spread across a range instead, like body weight in a litter of puppies.4Study.com. 5 Traits That Are Inherited in Animals They also rarely sort into tidy parent-offspring ratios, which is why two medium-size dogs can have pups of quite varied sizes. Even among many genes, a handful sometimes do much of the work.5Study.com. 5 Traits That Are Inherited in Animals
Each young animal gets two copies of every gene, one from each parent. A parent passes on only one of its two copies, chosen by chance, so siblings receive different combinations. A copy can also be present without showing: one working copy may mask a different one, so a parent can carry a version it never displays.
Scientists separate inherited from learned traits by asking whether the animal needed teaching. An inherited trait appears without it. To test this, researchers raise young away from their parents and from relevant experiences. If the trait still shows up, genes are a likely source, though conditions before birth or hatching can also play a part. Many traits turn out to be partly inherited and partly learned.
Trait 1 Coat Color and Pattern
Mammal fur gets its color from two pigments, a dark black-brown one and a reddish-yellow one. One gene, MC1R, builds a receptor on pigment cells that, when active, makes the cell produce black pigment.6PubMed Central. Agouti-Signaling Protein and Melanocortin-1-Receptor Mutations Associated with Coat Color Phenotypes in Fallow Deer (Dama dama) A partner gene, ASIP, makes a protein that blocks that receptor, so only reddish-brown pigment forms.7PubMed Central. Agouti-Signaling Protein and Melanocortin-1-Receptor Mutations Associated with Coat Color Phenotypes in Fallow Deer (Dama dama) In fallow deer, fur is black only when both copies of ASIP are broken and at least one copy of MC1R works.8PubMed Central. Agouti-Signaling Protein and Melanocortin-1-Receptor Mutations Associated with Coat Color Phenotypes in Fallow Deer (Dama dama)
The same two-gene system explains black versus brown alpacas.9Italian Journal of Animal Science. Interaction between the melanocortin 1 receptor (MC1R) and agouti signalling protein genes (ASIP), and their association with black and brown coat colour phenotypes in peruvian alpaca It works the same way across many mammals, from horses and camels to guinea pigs and leopards.10PubMed. Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus)11PubMed Central. Agouti-Signaling Protein and Melanocortin-1-Receptor Mutations Associated with Coat Color Phenotypes in Fallow Deer (Dama dama)
That also explains how two dark parents can have a lighter baby. If both parents carry the same hidden version and each passes it on, the baby gets two copies and shows the hidden color. Only some of the litter will show it, because each baby gets its own random draw from each parent.
Stripes need extra genes. In the African striped mouse, a gene called Alx3 is switched on in strips of skin before birth.12PubMed Central. Alx3 regulates the spatial differences in hair pigment underlying stripe patterns in rodents It slows the pigment cells there, leaving bands of lighter hair.13PubMed Central. Alx3 regulates the spatial differences in hair pigment underlying stripe patterns in rodents Zebrafish stripes form differently: different pigment cells touch and signal to each other, sorting themselves into a pattern.14PubMed. The Developmental Genetics of Vertebrate Color Pattern Formation: Lessons from Zebrafish
Trait 2 Body Size and Beak Shape
IGF1 makes a growth hormone that drives bone and body growth.15PubMed Central. A synonymous mutation in IGF-1 impacts the transcription and translation process of gene expression One version of the IGF1 gene is found in all small dog breeds and almost never in giant breeds.16PubMed Central. A single IGF1 allele is a major determinant of small size in dogs A single shared variant is a major reason a Chihuahua is small.17PubMed Central. A single IGF1 allele is a major determinant of small size in dogs A change in the gene for IGF1’s receptor is also strongly tied to shorter breeds.18PubMed Central. The insulin-like growth factor 1 receptor (IGF1R) contributes to reduced size in dogs
Because a few genes have big effects on size, breeders could change it fast. Choosing the smallest dogs to breed again and again can shift a whole line within a few generations. Many smaller genes then adjust leg length, skull shape and overall build, giving each breed its own proportions. Genes set a likely range, not a guaranteed number: a poorly fed animal can stay smaller than its genes allow.
Beak shape follows growth genes too. In Darwin’s finches, one stretch of DNA around a gene called ALX1 is strongly linked to beak shape.19PubMed. Evolution of Darwin’s finches and their beaks revealed by genome sequencing Different beak shapes let finch species eat different foods.20PubMed. Evolution of Darwin’s finches and their beaks revealed by genome sequencing In ground finches this shape changed quickly when food conditions changed.21PubMed. Evolution of Darwin’s finches and their beaks revealed by genome sequencing
In chickens and ducks, a growth signal called BMP4 sets overall beak size, and where it is active sets the shape.22PubMed Central. Morphoregulation of Avian Beaks: Comparative Mapping of Growth Zone Activities and Morphological Evolution Changing where that signal works turned a chicken beak into shapes resembling other birds’ beaks.23PubMed Central. Morphoregulation of Avian Beaks: Comparative Mapping of Growth Zone Activities and Morphological Evolution
Trait 3 Migration Direction in Birds
Two nearly identical willow warbler groups in Europe fly opposite ways, one southwest to West Africa and one southeast to eastern and southern Africa.24PubMed Central. Genetic Control of Avian Migration: Insights from Studies in Latitudinal Passerine Migrants Young hybrids of the two take an in-between route on their first autumn trip.25PubMed Central. Genetic Control of Avian Migration: Insights from Studies in Latitudinal Passerine Migrants Particular DNA regions are linked to each group’s direction.26PubMed Central. Genetic Control of Avian Migration: Insights from Studies in Latitudinal Passerine Migrants
Many young songbirds make that first trip alone and at night, with no adult to follow. They are born with an inherited heading and a rough sense of how long to keep traveling in that direction. They check the heading against Earth’s magnetic field and the pattern of stars. Birds read the magnetic field like a compass, using the angle of its field lines, and need light to do it.27PubMed Central. The discovery of the use of magnetic navigational information The inborn program gets them to the right region without a guide, but it is not a detailed map.
Birthplace still matters. When Dutch songbird eggs were hatched in Sweden, the birds wintered in places between Dutch and Swedish wintering areas.28PubMed. Innate factors and ontogeny determine nonbreeding areas of migrant songbirds
First-year birds often end up less precisely on target than experienced adults, because the inborn program is only a starting guide. On later trips, a bird can learn landmarks and good stopover places, and fine-tune its route.
Trait 4 Fear of Predators
Lab-raised young gobies that had never met a predator avoided an area showing a cod.29Marine Ecology Progress Series. Response of naïve two-spotted gobies Gobiusculus flavescens to visual and chemical stimuli of their natural predator, cod Gadus morhua They did have to learn to recognize cod by smell.30Marine Ecology Progress Series. Response of naïve two-spotted gobies Gobiusculus flavescens to visual and chemical stimuli of their natural predator, cod Gadus morhua So the fear of large fish is inborn, while the specific scent comes from experience. Young cichlid fish likewise inherit an ability to tell dangerous species from harmless ones.31Functional Ecology. Antipredator defences of young are independently determined by genetic inheritance, maternal effects and own early experience in mouthbrooding cichlids
A young animal that meets a predator for the first time may be eaten, so it cannot rely on learning from that first encounter. An inborn wariness of large or fast-approaching shapes costs little, since the worst outcome is some wasted caution. Learning then refines the response, teaching the animal which animals are truly dangerous and which only look alike.
Inherited fear can still be tuned. Minnows from rivers with pike school more tightly and dodge better than minnows from pike-free waters, even when raised in a lab.32Animal Behaviour. The inheritance and development of minnow anti-predator behaviour Early experience of a mock attack improved their defenses further.33Animal Behaviour. The inheritance and development of minnow anti-predator behaviour Populations that live with predators inherit a stronger readiness to learn from danger.34Animal Behaviour. The inheritance and development of minnow anti-predator behaviour
Trait 5 Songs and Calls
Closely related bird species tend to sound more alike than unrelated ones, even across both learned and unlearned calls.35PubMed Central. Phylogenetic signal in the vocalizations of vocal learning and vocal non-learning birds The pattern is strongest in songbird songs.36PubMed Central. Phylogenetic signal in the vocalizations of vocal learning and vocal non-learning birds
Some birds are born singers. Chickens and doves produce their typical calls correctly even if they never hear other birds make them. Songbirds such as canaries must hear adult birds to learn their full songs. Even so, learners inherit a template of what their own species’ song should sound like, which guides what they pick up. A young songbird raised alone sings only a rough version of its song.
Genes can also affect vocal ability itself. A change in FOXP2, a gene tied to vocal ability, is found only in Sumatran orangutans, which differ in vocal skills from Bornean orangutans.37PubMed Central. FOXP2 variation in great ape populations offers insight into the evolution of communication skills FOXP2 also matters for human speech, but the exact effect of the orangutan change is not yet proven.
Other Ways Parents Pass Things On
Mitochondria, the cell’s energy units, come only from the mother. In stickleback fish, eggs with more mitochondrial DNA produced fry that grew faster but died more often.38PubMed Central. Mitochondrial DNA content in eggs as a maternal effect
Because only mothers pass them on, natural selection tests a change in them only through females. A change that harms only males is therefore not weeded out, so such changes can build up, speeding male aging in fruit flies.39PubMed. Mitochondria, maternal inheritance, and male aging An egg also holds more than DNA: nutrients and other materials the mother put there before the young animal developed.
Another route is passing on gene settings rather than genes. In some invertebrates, heat stress changes which genes are switched on, and those settings can pass to offspring.40PubMed Central. Inheritance of Stress Responses via Small Non-Coding RNAs in Invertebrates and Mammals Offspring can inherit a parent’s experience without any change to the genes themselves.41PubMed Central. Inheritance of Stress Responses via Small Non-Coding RNAs in Invertebrates and Mammals
How Inherited Traits Come Bundled Together
Domestic animals share traits like floppy ears, patchy coats and smaller heads. Comparing village dogs with wolves found 246 DNA regions linked to domestication, many tied to early embryo cells that form face, skin color and stress glands.42PubMed Central. Comparison of village dog and wolf genomes highlights the role of the neural crest in dog domestication Breeding mainly for tameness likely changed looks too.43PubMed Central. Comparison of village dog and wolf genomes highlights the role of the neural crest in dog domestication Those same embryo-cell genes show extra selection in many domestic species compared with wild relatives.44PubMed Central. Neural crest cell genes and the domestication syndrome: A comparative analysis of selection
Early embryo cells migrate to build many body parts, including parts of the face, skin pigment cells and stress glands. A gene change in those cells can therefore touch coat color, ear shape and temperament all at once. That is why breeding for one trait can carry others along without the breeder choosing them.
Animals and plants also sometimes pick up useful genes by crossbreeding with related species.45PubMed. Adaptive introgression in animals: examples and comparison to new mutation and standing variation as sources of adaptive variation Red-backed fairywrens owe part of their plumage color to genes borrowed this way.46PubMed. Adaptive introgression of putative carotenoid pigment genes explains geographic variation in a sexually-selected plumage trait And in mice, some immune genes decide whether arthritis is inherited, but not how severe it is.47PubMed. Major histocompatibility complex controls susceptibility and dominant inheritance, but not the severity of the disease in mouse models of rheumatoid arthritis