a biblical example of applied genetics
Many people think that the Bible, especially the book of Genesis is outdated and at odds with modern science. They believe the biblical patriarchs were simple people with no concept of things like genetics or biotechnology. Creation Ministries International fully believes that Genesis is totally compatible with science, and that the Bible even makes better sense of the evidence than evolution. Interestingly, during my university studies, one of my genetics professors said that one of the first applications of genetics was recorded in Genesis 30–31, which describes a sheep breading program carried out by the patriarch Jacob! Humans have been performing artificial selection for millennia. This should be no surprise, since this is a major part of animal husbandry and plant breeding. To illustrate this point, let us examine the case of Jacob and his sheep in Genesis 30:25–31:12, where God even superintended a case of artificial selection.
Jacob and Laban’s deal
Jacob had already made a deal with his uncle, Laban, to work seven years to marry his daughter Rachel. But Laban deceived him, and gave him Rachel’s sister, Leah, instead. But Jacob loved Rachel more, so he voluntarily worked another seven years so he could marry Rachel as well.1 Jacob had worked for all those fourteen years to pay for his two wives. Now it was time to build up a nest egg. So, he offered Laban a deal:
“[Laban] said, ‘What shall I give you?’ Jacob said, ‘You shall not give me anything. If you will do this for me, I will again pasture your flock and keep it: let me pass through all your flock today, removing from it every speckled and spotted sheep and every black lamb, and the spotted and speckled among the goats, and they shall be my wages.’ (emphasis added) (Genesis 30:31–32)
Laban promises Jacob every speckled and spotted sheep and goat, and every black lamb as a reward for his labour. All the solid-coloured animals belonged to Laban. However, immediately afterward, Laban removes all the animals from his flock which are speckled, spotted, or black (verse 35), defrauding Jacob a second time! Laban took them on a three-day journey away from Jacob (Genesis 30:35–37). This way he thought he could prevent Jacob from breeding any coloured animals.
What can we tell from the way Jacob struck this deal with Laban? Apparently, motley-coloured and black animals were rare in Laban’s flock. Laban thought he would reap a great profit by receiving from Jacob the great majority of the flock. It was a killer deal he couldn’t refuse.
Before we get into the explanation of what happened, please understand that coat color in sheep and goats is very complicated. Multiple genes are involved, and the environment and age of the animal are also factors. Worse, since the Bible does not to give us a detailed description of the pedigree of Jacob’s flocks, it is difficult to deduce exactly what transpired.
To further add to the complexity of the situation, we do not have the ability to go back in time and study the genetics of Laban and Jacob’s flocks. The animals could have carried genetic variants that no longer exist. These variants could have been lost to time and chance. That is, the lineage could have died out. Or the original genes could have been mutated. The animals could also have carried a combination of traits that no longer are found together. ‘Linkage’ is an important factor in many complex genetic systems, yet chromosomal recombination will eventually break even tightly linked genes. Even though we do not have all the details, we can still make some educated guesses about Jacob and his livestock.
How could Jacob increase the number of motley-coloured animals?
Laban cheated Jacob again by taking off with the motley and darker coloured animals. How was Jacob to receive any of his wages this way if he didn’t have any of these animals in his possession? How is it that some motley-coloured animals were born in the flock after Laban had left?
A recessive trait?
Animals, plants, fungi, and single-celled protists (basically, everything but bacteria) are ‘diploid’, meaning there are two copies of the genome in every cell. A genome is subdivided into sections called genes, which are sections of DNA that code for protein. We get one set of genes from our father and one from our mother. Since the genome is present in two copies in each cell, each gene is also present in two copies. Genes often come in several variants. We call these alleles. A recessive allele can be masked by a dominant allele. The dark-colour alleles are recessive in sheep and goats.2
We can surmise that many of the solid-coloured animals in Jacob’s flock were so-called heterozygotes. A heterozygote is an animal which has two different variants (alleles) of a given gene. The Greek word ‘hetero’ means different. We usually write the genetic status of a heterozygote like this: Aa. This simply means that the animal carries a dominant allele (A) and a recessive allele (a). A homozygote is an animal which has two of the same variants of a given gene (denoted as either AA or aa). For a visual representation of homozygotes and heterozygotes, see figure 1. This is only a general way of writing gene symbols. Scientists can choose any combination of letters (i.e. S/s, R/r, W/w, etc.), if they note what letter means what.
As stated above, if white is a dominant trait, this means the flock Laban left Jacob could still contain some alleles for motley colour, despite all the animals being solid white. But the animals are described as being speckled, spotted, and even striped, which suggests different gene categories. Being that so many different varieties are mentioned, we should be looking for a more complex answer.
Changes in gene expression over time
Also, there is a question about why some lambs were solid black, whereas the parents were motley-coloured? Wool colour in sheep and goats could also change over time. We know this happens in many other animal species. For example, in humans, hair colour might be lighter at a younger age. It might be surprising if an all-black lamb matured into a motley-coloured adult. However, without access to Jacob’s animals, we cannot say anything for certain.
Coat colour could also be caused by something known as ‘incomplete penetrance’ (figure 2, first row). In complete penetrance, every individual manifests the trait that the allele codes for. With incomplete penetrance, only some individuals with the allele show the trait. This is common in genetic illnesses. For example, 48% of women who carry the BRCA1 gene variant develop breast cancer by the age of 80.3 Therefore, the penetrance is 48% for this allele. In some cases, incomplete penetrance means that the allele in question does not manifest to the fullest degree possible. This could be due to other genetic cofactors. In the case of Jacob’s sheep, incomplete penetrance might cause white stripes, spots or speckles to appear on an otherwise black background.
Another possibility is that coat colour is ‘co-dominant’ (figure 2, middle row). This means that multiple alleles can be expressed at the same time. Homozygotes will show only one trait. But the heterozygotes will show a blend. An example of co-dominance appears in some flowers, where the homozygotes are red or white, and the heterozygote is in between: pink. Thus, it is possible that the spotted, speckled, or striped coat colour of sheep is in between a solid dark colour and a solid white colour in Jacob’s sheep.
A third possibility is what are known as X-linked recessive traits (figure 2, bottom row). What does this mean? The X chromosome is a ‘sex chromosome’, which is different than all the other chromosomes. Females carry two X chromosomes, whereas males carry and X and a Y chromosome. However, the Y chromosome is much, much smaller than the X chromosome. So much smaller that it contains only a handful of genes (figure 3). Therefore, in males, whatever gene is located on its X chromosome is always expressed. Even if the gene is recessive, it gets expressed, because there is no dominant allele on the X chromosome to hide it. Males are ‘hemizygous’ for the great majority of genes on the X chromosome. In humans, balding patterns, hemophilia, and red-green colour blindness are all X-linked traits that predominantly affect males.
Interestingly, in females, only one X chromosome is expressed in each cell. The other X chromosome gets deactivated. This is another way that the sex chromosomes differ from the other chromosomes. The deactivated X chromosome is coiled up tightly and can be seen under a microscope. The resulting lump is called a ‘Barr-body’. If the female has an allele for darker colour on one of its X chromosomes, and an allele for lighter colour on its other X chromosome, the female could be of mixed colour, depending on which stage of development the X chromosomes get inactivated.
Cats are a good example of this. Calico cats are black and orange. These cats are always female. This particular colour trait is carried on the X chromosome. Male cats can only be either black or orange. But in females, due to the way sex chromosomes are deactivated during fetal development, female heterozygotes will have both black and orange blotches on them (figure 4).
An X-linked recessive gene could possibly be behind coat colour in sheep. If one or a few darker rams were selected to mate exclusively with all the ewes, this could effectively spread motley-colour among the flock. Since the ram has only one single allele, he can only pass on either this darker-colour causing allele on his X chromosome to the ewes, or his Y chromosome, which lacks the gene entirely. The ewes would pass on only one of their X chromosomes. Thus, the all the female lambs would be heterozygous or homozygous recessive. The male lambs would be hemizygous, but since the motley colour gene would be rare, at least initially, most would be white (figure 5).
Clearly, X-linked patterning cannot explain everything that is happening. Yet, since we are dealing with a multi-allelic and multi-gene system, it could certainly be playing a role.
Gene dosage effects
Yet another possibility is that coat colour in sheep is caused by more than one copy of a gene, something known as a dosage effect. Indeed, some researchers have found that in sheep, the ASIP gene regulates the production of pigment in wool. Fewer copies of the gene cause black coat colour, which is recessive. A higher copy number of the gene causes the dominant white coat colour.4
It is even possible that more than a single gene is involved. Today’s technology allows scientists to monitor the level of expression of all the genes in the genome. Some researchers found that around 2,200 genes are differentially expressed between black and white Merino sheep.5 Most of these have nothing to do with coat colour, but if genetic expression can show such a profound variation within a single, modern breed, it would be a mistake to think that Jacob’s animals were somehow different. Perhaps the story seems so strange to us because there is nothing in modern sheep and goats to compare to.
Multiple alleles of the same gene
Interestingly, one research group found that there are multiple differences among three coat colour variants in goats.6 It is possible that there are three different versions (alleles) of the same gene, or there could be three separate genetic pathways involved.
In rabbits, multiple alleles of the same gene lead to many different fur colours (figure 6). The dominant allele codes for a dark pigment which is absorbed into the animal’s fur. Another allele, called ‘chinchilla’, is less effective at pigment production. A third allele, called ‘Himalayan’, produces a variant that operates only within a certain temperature range. A fourth allele produces no pigment at all. This is called the ‘albino’ allele and the rabbit with this only this allele is completely white.
Yet another factor that affects coat colour is which genes are turned on and off at any given time. The process is referred to as epigenetics, and it is the bane of Darwinian evolution. Most of the switching is controlled by environmental cues. Hence, the colour of an animal could be due to what it is eating or to any number of other environmental factors, and the cue could have happened in an earlier generation. The ability to switch genes on and off, even across generations, only increases the potential complexity of any explanation of what happened among the flocks living on the hills of Paddan Aram about 4,000 years ago.
What happened at Jacob’s watering troughs?
In Genesis 30:37–43, we read about how Jacob manipulated the flocks so that he increased the number of striped, spotted and speckled animals. But one section of this account has caused much confusion and speculation. It has to do with some sticks that Jacob cut, peeled, and placed in the watering troughs when the strong males were present:
“Then Jacob took fresh sticks of poplar and almond and plane trees, and peeled white streaks in them, exposing the white of the sticks. He set the sticks that he had peeled in front of the flocks in the troughs, that is, the watering places, where the flocks came to drink. And since they bred when they came to drink, the flocks bred in front of the sticks and so the flocks brought forth striped, speckled, and spotted.” (Genesis 30:37–39)
Why did he use these three tree species? Some have suggested they had medicinal properties or even that Jacob was drugging the ewes. Some even suggest Jacob attempted to use some sort of magic. In Genesis 31:19 we read about how Rachel stole Laban’s household gods. Perhaps he was into superstitious practices as well.
But all of this is doubtful. Not only would he have required a lot of material to drug the entire water supply, but the trees themselves are not that special. The plane tree (Platanus orientalis), which prefers wet soils, is related to the North American sycamore. ‘Poplar’ could refer to the black poplar (Populus niger) or the white poplar (Populus alba). These trees also prefer wet soils and are related to the aspen and cottonwood. There is nothing medicinally special about them. The almond (Prunis dulcis), however, does produce a significant amount of cyanide, hence people who experience mild cyanide poisoning will report the smell or taste of almonds. In fact, most of the members of the Prunus genus produce cyanide, including apples and peaches. Had Jacob fed the bark to the animals, that could potentially have an effect. This would more likely be due to the nutritional yield than to any potential medicinal effects. But the Bible says nothing about him feeding the animals any of the bark. Placing the sticks in or near the water source would probably have had no chemical effect, either.
Thus, one would assume the stripes Jacob peeled in the bark were not important from a medicinal standpoint. And the stripes had nothing to do with reproduction in these animals. It is possible that Jacob associated the striping with the resulting color of the lambs, but this is contradicted by the other statement that Laban switched the deal on Jacob several times (Genesis 31:7). Jacob could have placed them into the troughs to attract or entrap the ewes, making it easier for the desired males to mate with them, to temporarily corral ewes and the desired rams together, or to exclude or pen up the undesired males.
We simply don’t have enough details. The one thing we do know is that there were stronger (Genesis 30:41) and weaker males and that Jacob could control the appearance of the lambs and kids by controlling which males bred. In effect, Jacob was using artificial selection to influence the coat colour of the lambs that were born to the flock.
Jacob dreamed the whole thing
There is an important part of this story that many people miss. We are not told until Chapter 31, but God showed Jacob what was going to happen in a dream.
“In the breeding season of the flock I lifted up my eyes and saw in a dream that the goats that mated with the flock were striped, spotted, and mottled. Then the angel of God said to me in the dream, ‘Jacob,’ and I said, ‘Here I am!’ And he said, ‘Lift up your eyes and see, all the goats that mate with the flock are striped, spotted, and mottled, for I have seen all that Laban is doing to you. I am the God of Bethel, where you anointed a pillar and made a vow to me. Now arise, go out from this land and return to the land of your kindred.’” (Genesis 31:10–13)
Therefore, it does not even matter what Jacob thought. He could have had absolutely no clue about the genetics. This is unlikely, because as a long-term shepherd he would have had plenty of time to observe which rams were mating with which ewes and what the results were. Yet, all he had to do was follow God’s instructions. If only the motley-coloured rams were breeding, this would have insured that the genes for those coat colours would have quickly become the most common genes in Laban’s once-white flocks.
Multiple alleles? Multiple genes? God’s providence?
A part of the passage we are examining could suggest that several gene variants, or even several genes are behind the inheritance patterns behind coat colour. In Genesis 31:5–8, we read:
“I see that your father does not regard me with favor as he did before. But the God of my father has been with me. You know that I have served your father with all my strength, yet your father has cheated me and changed my wages ten times. But God did not permit him to harm me. If he said, ‘The spotted shall be your wages,’ then all the flock bore spotted; and if he said, ‘The striped shall be your wages,’ then all the flock bore striped.”
It appears from this verse that Laban had gotten wind of Jacob’s early breeding success. He might have been quite surprised to learn how Jacob had turned the tables on him by using artificial selection and increasing the number of motley-coloured animals in his flock. Thus, Laban’s response would have been to try to cheat Jacob yet again by changing their agreement, not once, but ten times. This would mean that Jacob was tending Laban’s flock for a space of ten years, since breeding season happens only once a year.
This time, Laban didn’t even agree to giving Jacob all the motley-coloured animals, but rather only a sub-set of the animals. Laban could have been getting desperate. At one time, he’d allow Jacob to have only the spotted animals. Then, in God’s providence, the flock would give birth to spotted animals. Since there were so many spotted among the flock, the next time Laban would change the agreement so that Jacob could only have the striped animals. Then the striped animals would increase rampantly. And so on, and so forth. Laban must have been getting really frustrated!
Perhaps something supernatural was going on in the background. If Jesus could have multiplied a few loaves of bread to feed the five thousand people (Matthew 14:14–19), then God could also have been superintending which alleles were being passed on in of the flocks each time Laban changed Jacob’s wages.
There are many possible explanations behind the heredity of wool colour in Jacob’s sheep. We don’t exactly know which genes play a role, because this breeding program happened several thousand years ago. Researchers are only now beginning to understand the genetics behind wool colour in sheep and goats. In the case that wool colour is caused by more than one gene, we don’t even know how tightly linked they were to one another. Ever since then, the genes could also have undergone mutations or been shuffled around or separated from one another.
The Bible also isn’t clear enough in this passage for us to draw hard and fast conclusions. But this might not be important. What we do know is that Jacob did apply selective criteria to separate the sheep and goats based on their colour patterns. He might not have understood himself the exact genetic principles behind the selective procedures, but the result is that he was able produce a large number of motley-coloured animals, with divine guidance.
References and notes
- He would have married her after the bridal week with her sister was complete. Jacob did not have to wait 14 years to marry Rachel. See Genesis 29:27–30. Return to text.
- Aaron, D.K., Basic Sheep Genetics, casey.ca.uky.edu/files/asc220_basic_sheep_genetics.pdf, accessed 5 February 2020. Return to text.
- Anglian Breast Cancer Study Group, Prevalence and penetrance of BRCA1 and BRCA2 mutations in a population-based series of breast cancer cases, Br J Cancer 83(10):1301–8, 2000. Return to text.
- Norris B.J. and Whan, V.A., A gene duplication affecting expression of the ovine ASIP gene is responsible for white and black sheep, Genome Res. 18(8):1282–93, 2008. Return to text.
- Fan, R., et al., Skin transcriptome profiles associated with coat color in sheep, BMC Genomics 14:389, 2013. Return to text.
- Peng, Y., et al., Skin transcriptome profiles associated with coat color in goat, biorxiv.org/content/10.1101/028340v1, accessed 24 March 2020. Return to text.