Presentation on theme: "AGRICULTURAL GENETICS By C Kohn Waterford Dept of Agricultural Sciences."— Presentation transcript:
AGRICULTURAL GENETICS By C Kohn Waterford Dept of Agricultural Sciences
Locker and Heritability Locker the Steer was a good example of heritability. Locker was very similar to his mother, grandmother, and great-grandmother and resembled them ways that included… Appearance – he looked like they did (color, face, etc.) Structure – his skeletal frame was very similar Attitude – he behaved in similar ways and had the same kinds of “quirks”, like opening gates and loving chin rubs Did he do this because of genetics, or because of Mr. Kohn? Which things are genetic? Were they completely genetic, or a mix of how he was raised and the genes he had? TPS
Genetic Inheritance Overview Genetic traits are passed from parents to their offspring. Each parent provides one copy from each pair of chromosomes (humans have 23 pairs of chromosomes). A chromosome is just a ‘package’ or ‘bundle’ of tightly-packed DNA. In humans, 23 chromosomes come from your mother and 23 from your father. Each chromosome has a portion of all of the genes in the body All chromosomes together carry all the genes of the body. Each cell’s nucleus contains the same chromosomes that every other cell in the body has This is due to the fact that every cell came from one cell – the fertilized egg cell that become the organism. Source: 29lifescience.wikispaces.com
Inheritance Review Because each offspring has two copies of each chromosome (maternal and paternal), they will have at least two copies of every gene. The gene, or section of DNA for a specific trait, will code for the proteins responsible for every trait in the body. As we’ve previously discussed, one copy of a gene affects another copy of the same gene For example, Mr. Kohn has a gene for blue eyes and a gene for brown eyes However, only one of the genes is visible as the phenotype. In cattle, ‘no horns’ is dominant to ‘horns’. If a cow is heterozygous for horns, they won’t have any (even though they have a gene for horns) The horn gene is recessive to the polled (no horns) gene. Source:
Darwin and Mendel The 19 th century work of Charles Darwin and Gregor Mendel paved the way for a genetic revolution in agriculture. Darwin demonstrated how a species can change as a result of either natural or artificial selection. Mendel demonstrated inheritance patterns shown by Punnett squares. Watson and Crick’s discovery of DNA further paved the way for dramatic increases in ag productivity through biotechnology. Knowing that species can change, and knowing how they change generation to generation, was pivotal in revolutionizing the agriculture industry.
Early Ag Genetics Prior to 1900, most agricultural breeding was the result of trial and error, with little understanding of how or why it worked. Cattle are a classic example; all major American breeds of cattle are originally from Europe. A breed is a specific variety of a species of domesticated animal with similar traits and qualities. All breeds of cattle came from the ancient Taurine species of cattle. Thousands of years ago, early civilizations began to trap and tame these animals. Having a source of meat at all times provided more stability to early civilizations.
Origins of Cattle Breeds After they were domesticated, early cattle breeding occurred in isolated places. Because early peoples had little communication with each other and rarely strayed from their groups Over time, widely different kinds of cattle in an area would become less diverse as some traits were selected more than others. With little outside interference, the cattle in one village would look more like each other. They would also look less like cattle from other communities. Because of this breeds with specific characteristics developed.
Why breeds of cattle are different. Different climates and environments selected for different traits. Cold harsh weather necessitated selection for hardiness and survivability. Lush pastures provided opportunity to select for high production levels. Scarcity of feed on the other had forced locals to select for efficient grazing. The environment of each portion of Europe resulted in different kinds of cattle. Dairy cattle show some of the most distinct differences.
Breeds of Dairy Cattle With its lush pastures and fertile cropland, Holland created the largest and most productive breed of dairy cattle – the Holstein.
Breeds of Dairy Cattle The inhabitants of the islands in the English Channel selected for cattle that were small, efficient, and produced rich milk that was high in butterfat for their cheese and butter production. This led to the rise of the Jersey breed, among others.
Breeds of Dairy Cattle The mountains of Switzerland created the need for strong, hardy cattle that could withstand the cold winters and rocky terrain. These needs led Swiss farmers to select for the traits common to the Brown Swiss breed.
Breeds of Dairy Cattle The desire for a multi-purpose animal in England led to the rise of the Milking Shorthorn breed – an early breed that could be used as both a milking animal as well as a meat animal.
Other Dairy Breeds Other dairy breeds include – Guernsey – high quality grazing animals Ayrshire – deep red cattle Red and White Holsteins – identical to regular Holstein cattle except that they have a recessive red color. Due to their initial isolation, different regions of Europe produced their own “brands” of cattle that were unique to the needs of the region in which they were developed. These breeds of cattle were created not by survival of the fittest individuals for their environment (as in natural selection) but by artificial selection – Artificial Selection: the selective breeding of plants and animals by people to enhance specific qualities or traits (such as milk production).
How does someone “select” for a trait? Imagine you have two cows, Anna and Bessy. If Anna has better production than Bessy, you are probably going to keep Anna for breeding and sell Bessy for meat. The same would be true for bulls If Charles the Bull has calves with really good production and Darryl does not, Charles will be kept to breed Anna and Darryl will be sold for meat. By selecting both Anna the Cow and Charles the Bull, you would hopefully produce a second generation of cattle with a greater milk production. Over years and years, you will slowly increase the average milk production of every cow by selecting the best animals to breed.
Breed Associations As the benefits of selective breeding became better understood, breed associations began to form Their mission was to support farmers as they developed better, more productive breeds. They kept track of the performance of different bulls by ‘scoring’ their offspring for different traits. Organizations such as the National Holstein Association and the American Jersey Cattle Association provided farmers with data on different bulls. This data allowed individual farmers to select bulls with traits they needed for their herd. For example, if you cows generally milk very well but have very poor feet and legs, you would pay special attention to bulls who have offspring with very good feet and legs.
Dr. Stephen Babcock A major Wisconsin contribution to this process was made by Dr. Stephen Babcock of the University of Wisconsin. Prior to Babcock’s work, there was no reliable way to test the quality of milk from each cow and from each farm. This meant that dishonest grocers, dairies, or farmers could dilute their milk with water in order to increase the weight. It also meant that it was hard to tell if a cow was producing high or low quality milk. Quality of milk is mostly determined by the amount of butterfat in the milk. Babcock’s test not only helped prevent adulteration of milk but provided a basis by which to improve dairy genetics. It was also the first world-renown scientific achievement at UW-Madison. This put Wisconsin on the map of the scientific world and spawned a rich tradition of excellence in scientific research.
Artificial Insemination (AI) The development of artificial insemination (AI) was also critical, particularly in the dairy industry. AI is a process in which semen is collected from a bull, packaged into straws, and frozen and shipped to individual farms so that it can be artificially inserted into a cow’s reproductive tract. This is different from natural insemination (when a bull directly breeds a cow.) AI enables one bull to inseminate thousands of cows, reducing the need for bulls on every farm. Instead of only having access to bulls in the area, you could improve your herd’s genetics by introducing high quality genetics from across the world. The use of AI required farmers to understand the principles of inheritance. Inheritance is the measure of how efficiently a trait can be passed from generation to generation.
Heritability Heritability is a measure of how likely offspring are to inherit the phenotypes of their parents In other words, it is a way to determine the impact of both the genotype of the parents as well as the impact of the environment and care on the phenotype of the offspring For example: if we have a cow that produces a lot of high-quality milk, what is the likelihood that she will have daughters that also produce large amounts of high-quality milk? This question is incredibly important because it determines the amount of money a farmer will make more so than anything else.
Heritability Measurements The heritability value (or h 2 value) is a measure of how likely a phenotypic trait is caused by the genes of the parents and how much is caused by the environment in which the animal lives. For example, you can see the value for milk yield for Holsteins is This means that 30% of milk production is because of genetics, and 70% is because of their environment and care (diet, nutrition, health, weather, etc.). Productive life is only 13% affected by genetics (and 87% by how well you care for your animals).
How Heritability is Used Heritability tells a producer how much they can improve aspects of their herd through genetics and bull selection. A trait with heritability over 40% (or 0.40) would be a trait that could more easily be changed through genetic selection. For example, you can easily improve the quality of the milk you produce through a selection of bulls that typically have daughters with high butterfat content). On the other hand, some traits are affected little, if at all, by genetics. E.g. the length of the life of a cow has a very low h 2 value, meaning that how well you care for the animal means far more than the genotype of that animal’s parents. A h 2 value under 15%, or 0.15, means that genetics really do not play a major role in that particular trait.
How Herd Genetics Change Improving the overall genetics of a farmer’s herd involves 4 key factors: Accuracy of Selection: rate of choosing only highest genetic-quality animals Selection Intensity: Proportion of herd animals kept for breeding each generation Genetic Variation – how varied your herd animals are for each trait Generation Interval – the herd’s rate of reproduction To obtain faster genetic change, you need excellent animal genetics, highly inheritable traits, and rapid maturation and reproduction.
Galton’s Law What can make genetic improvement difficult is a phenomenon known as Galton’s Law. Galton’s Law states that the more extreme a trait, the less likely the offspring of the parent’s with that trait are to acquire it at the same intensity. Source:
Galton’s Law For example, in 2010 a cow in Sheboygan County set a new world record for most amount of milk produced in a single year at 72,170 lbs. Even though this animal must have exceptionally superior genetics, it is exceedingly unlikely that her daughters will produce as much milk as her. In all likelihood, her daughters will produce more milk than average, but not as much as their mother. As a trait becomes exceptionally high or low, it’s likelihood of being expressed in the same way by the offspring is less and less. Phenotypic traits tend to stay near the average for a population.