Lesson #1 - Weebly



Equine Science & Technology

Unit Title: Horse Genetics CIP: 020221-08

Instructor:

Objectives:

After completing this unit of instruction, students will be able to:

A. Explore the fundamentals of genetics;

B. Define a gene;

C. Distinguish between qualitative and quantitative traits;

D. Investigate horse coat color and markings; and

E. Explain the heritability of performance traits.

Click here for this lesson’s PowerPoint presentation

Interest Approach:

Break students into small groups. Assign them to individual research projects. Have them determine the proportion of students in the class according to:

- Hair color

- Eye color

- Tall/Short

- Large feet/Small feet

- Other genetic features

Ask the class why genetics are important.

Define genetics with the class and discuss various job opportunities in the field of genetics.

Genetics – The branch of biology that deals with heredity, especially the mechanisms of hereditary transmission and the variation of inherited characteristics among similar or related organisms.

Curriculum & Instruction

|Curriculum |Instruction |

| | |

|A. Explore the fundamentals of genetics. |PowerPoint presentation: |

| |“08 Horse Genetics.ppt” |

|Nature ordained that genetics be applied to horse breeding long before there were geneticists. | |

|Prior to the domestication of horses, there was natural selection for speed and stamina. One of the|A1. Lecture with discussion. |

|most important defense mechanisms of the horse was to outrun its enemies. | |

|Natural selection was probably very effective in improving speed and endurance, since the slower | |

|horses were eliminated by predators. | |

|Many horse breeders have been practicing genetics as they concern themselves with the art of | |

|breeding. Their guiding concept of heredity is that “like begets like”. | |

|Breeders in the 18th century made a tremendous contribution in pointing the way toward horse | |

|improvement before Mendel’s laws became known to the world. | |

|As knowledge of genetics developed, there evolved an understanding of the science that underlies | |

|the art of horse breeding. | |

| | |

| | |

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|B. Define a gene. | |

| | |

|The bodies of animals are made up of millions or even billions of microscopic cells. | |

|Each cell contains a nucleus in which there are a number of pairs of bundles called chromosomes. | |

|In turn, the chromosomes carry pairs of minute particles called genes, which are the basic | |

|hereditary material. | |

|The nucleus of each cell of a horse contains 32 pairs of chromosomes, or a total of 64. |B1. Lecture with discussion. |

|There are thousands of pairs of genes on each chromosome. | |

|Genes determine all the hereditary characteristics of animals from the body type to the color of |B2. Build in actual examples with pictures|

|the hair. |of horses with different colorings. |

|The mule has an uneven number of chromosomes and cannot reproduce. | |

|The genotype of an animal refers to the specific genes it possesses on its chromosomes. | |

|Genome describes the complete set of “instructions” for making an organism. | |

|Dominant gene expression has a full allele effect. An example would be when a gray horse produces | |

|a gray horse. | |

|Recessive character appears only when both members of a pair of alleles are alike. | |

|The job of transmitting qualities from one generation to the next is performed by the germ cells – | |

|a sperm from the male and an ovum, or egg from the female. | |

|There are alternate forms of each gene. The alternate gene forms are referred to as alleles. If the| |

|alleles are the same, the condition is referred to as homozygous. If the alleles are different, the| |

|condition is called heterozygous. | |

|Selection and closebreeding are the tools through which the horse breeder may obtain stallions and | |

|mares whose chromosomes and genes contain similar hereditary determiners – animals that are | |

|genetically more homozygous. | |

|Gene changes are known as mutations. A mutation may be defined as a sudden variation that is later | |

|passed on through inheritance and that results from changes in a gene or genes. | |

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|C. Distinguish between qualitative and quantitative traits. | |

| | |

|Simple Gene Inheritance (Qualitative Traits) | |

|In the simplest type of inheritance, only one pair of genes is involved. Thus, a pair of genes may | |

|be responsible for the color of body hair in horses. |B3. Closebreeding – The mating of closely |

|The idea that certain basic colors may have a rather simple explanation of inheritance should not |related animals. |

|alter the fact that other genes may play an important role through their influence on basic | |

|schemes. | |

|The possible gene combinations are governed by the laws of chance. | |

|Other possible examples of simple gene inheritance in horses might include eye color and the set | |

|(placing) of the ears on the head. | |

| | |

|Dominant and Recessive Alleles | |

|A dominant allele may cover up a recessive allele. Therefore, a horse’s breeding performance cannot| |

|be recognized by its phenotype (how it looks). | |

|Recessive genes can be passed on from generation to generation, appearing only when two animals, | |

|both of which carry the same recessive allele, happen to mate. | |

|Reputable purebred breeders have an obligation, not only to themselves, but to their customers. |C1. Lecture with discussion. |

|Purebred animals must be purged of undesirable genes by eliminating those stallions and mares that | |

|are known to have transmitted the undesirable recessive gene. | |

| | |

|Incomplete Dominance | |

|In some cases, dominance is neither complete nor absent, but incomplete or partial and expresses in| |

|a variety of ways. | |

|Perhaps the best known case of this type in horses is the palomino color. Genetic studies of the | |

|Palomino indicate that the color is probably unfixable – that it cannot be made true breeding, no | |

|matter how long or how persistent the effort. | |

| | |

|Multiple Gene Inheritance (Quantitative Traits) | |

|Important characters such as speed are due to many genes. Thus, they are called multiple-gene | |

|characters. | |

|Quantitative inheritance refers to the degree to which a characteristic is inherited. | |

|For example, all Thoroughbred horses can run and all inherit some ability to run, but it is the |C2. Refer back to the interest approach |

|degree to which they inherit the ability that is important. |studies. Discuss how some of the traits |

|In quantitative inheritance, the extremes (either good or bad) tend to swing back to the average. |are dominant and some recessive. |

| | |

|D. Investigate horse coat color and markings. | |

| | |

|Recent advances in genetics have allowed us to understand better how coat color is inherited. This| |

|makes it possible to plan matings that will produce foals of a certain color. | |

| | |

|Gene A | |

|Genetic control of black color restricted to the points of a horse is through gene A, or the A | |

|allele. | |

|The A allele is dominant. | |

|A uniformly black horse has the recessive genotype aa. | |

| | |

|Gene E | |

|Gene E, or the E allele, controls the expression of black hair on the body. | |

|The recessive form ee, results in uniformly red-colored horses. | |

|The E gene is related to (and can mask) the A gene. | |

| | |

|Gene G | |

|Gray coloring is due to the dominant gene G. | |

|Any horses with the G allele will be gray; non-gray horses will have the genotype gg. | |

|Gray horses can be born any color. | |

| | |

|Gene W | |

|Solid white coloring is controlled by gene W. | |

|The dominant homozygous (WW) condition is lethal; thus, all white horses have the genotype Ww. | |

|All non-white horses have the genotype ww | |

| | |

|Genes C and D | |

|The C and D alleles are dilution alleles. Gene C affects only red pigment and causes the pigment to| |

|lighten. |D1. Refer to the horse pictures once |

|The C gene does not affect black pigment. |again. |

|Gene D differs from gene C in that it can dilute both black and red pigment. | |

|With the D allele, black is diluted to a mouse or slate grey, and red is diluted to a yellow-tan. | |

|Horses with the D allele also show primitive marks, such as the dorsal stripe, shoulder stripes, | |

|and leg barring. | |

| | |

|Gene TO | |

|The spotting of paint and pinto horses is controlled by the tobiano gene TO. | |

|The tobiano color pattern is dominant; thus, overos must have the genotype toto. | |

|Homozygous TOTO horses are rare and are sought after by horse breeders for their ability to always | |

|produce spotted foals. | |

|Genetic tests are available to determine whether a horse is homozygous. | |

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|E. Explain the heritability of performance traits. | |

| | |

|Relatively little scientific work has been done on the heritability of performance of horses-on the| |

|genetics of working ability, racing ability, cutting ability, etc. | |

|The horse is the last farm animal to which the science of genetics has been added to the art of | |

|breeding | |

|Differences in the performance ability (working, racing, jumping) are due to two major forces – | |

|heredity and environment | |

|The important environmental factors in determining the overall performance of horses are nutrition | |

|(both prenatal and postnatal), health care, quality of training, ability of the handler, and | |

|injuries. | |

|An important genetic principle is that traits as such are not inherited. The ability to respond to | |

|a given set of environmental conditions in order to produce a trait with a measurable effect is | |

|inherited. | |

|Reliable estimates on the heritability of performance traits in horses are limited in comparison | |

|with those for other species. | |

| | |

|The following conditions would tend to indicate a hereditary defect in horses: | |

|If the defect had previously been reported as hereditary in the same breed. | |

|If it occurred more frequently within certain families or when there had been inbreeding. | |

|If it occurred in more than one season and when different rations had been fed. | |

| | |

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| | |

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|The following conditions might be accepted as indications that the abnormality was due to a | |

|nutritional deficiency: | |

|If it had previously been reliably reported to be due to a nutritional deficiency. | |

|If it appeared to be restricted to a certain area. | |

|If it occurred when the ration of the dam was known to be deficient. | |

|If it disappeared when an improved ration was fed. | |

Review & Evaluation

Objectives will be reviewed before examinations. Exams will be developed based on objectives as taught in class.

Instructional Support

A. References

Ensminger, M. E. (2004). Equine Science (8th ed.). Upper Saddle River, N.J: Prentice Hall

B. Teaching Aids and Equipment

- Overhead projector

- Board with chalk/marker

C. Facilities

- Room _____________

Name_____________________________ Date________________

Equine Science and Technology

Horse Genetics

Quiz

Multiple Choice. Circle the correct answer.

1. Chromosomes carry pairs of _____ which contain hereditary material.

A. Dispositions

B. Genes

C. Germs

D. Mutations

2. What is the technical term for the change in a gene?

A. Allele

B. Homozygous

C. Mutation

D. Overdose

3. Which gene combination produces a Gray foal?

A. GG

B. Gg

C. gG

D. gg

4. The _____ of an animal refers to the specific genes it possesses on its chromosomes.

A. Allele

B. Genotype

C. Heredity

D. Phenotype

5. Each cell contains a nucleus in which there are a number of pairs of bundles called

A. Chromosomes

B. DNA

C. Genes

D. Homozygous

6. Dominance gene expression has a _____ allele effect.

A. Full

B. Half

C. Minor

D. Slow

Matching. Write the correct letter of the item next to the description. The item may be used once, more than once, or not at all.

|Description |Item |

| | |

|_______ Controls the expression of black hair on the body. |32 |

| |64 |

|_______ Describes the complete set of instructions for making an organism. |ee |

| |Eye color |

|_______ Overos have this genotype. |Gene E |

| |Genome |

|_______ Results in uniformly red-colored horses. |Heterozygous |

| |Homogenous |

|_______ The alleles are different. |Homozygous |

| |toto |

|_______ The alleles are the same. |TOTO |

| |WW |

|_______ The horse has ____ pairs of chromosomes. | |

| | |

|_______ This condition is lethal in horses. | |

Equine Science and Technology

Horse Genetics

Key

Multiple Choice

1. B

2. C

3. A

4. B

5. A

6. A

Matching

7. E

8. F

9. J

10. C

11. G

12. I

13. A

14. L

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