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Ai manual chapter 10
- 6. Gamete and Zygote Formation
- 12. Chromosomes That Determine Gender
Editor's Notes
- The quantity and quality of milk and meat are largely determined by inheritance. To make good genetic selections we need to have a basic understanding of heredity.
- Genes are the units of inheritance determining an individual’s characteristics. Each gene is a segment of a thread like structure called a chromosome. Cattle have 30 pairs of chromosomes, a hog has 19, man has 23.
- Where there once was one cell there are now two.
- Cells dividing and multiplying is what cause the animal to grow and produce.
- To reproduce the species, a different process occurs. Here the male (sperm) and the female (egg) have one of each pair of chromosomes. When fertilization happens the one from the male and the one from the female pair-up, forming all the hereditary units for the new individual.
- Note the pairs in the fertilized egg.
- DNA tells cells what to do and when to do it. Stores and passes on hereditary information by using chemical messengers (RNA).
- Remember genes come in pairs; they can be homozygous or heterozygous. Some are dominant, others recessive. Every animal is made up of genotype and phenotype. Genotype = what it inherited. Phenotype = what the animal exhibits: udder shape, production, growth − that can be seen and measured.
- This diagram shows what happens when the dominant gene for polled is homozygous in one parent and the recessive gene for horned is homozygous in the other are mated. All the offspring will be polled.
- Here’s what happens when heterozygous parents carrying both the polled and horned gene are mated. Phenotypically 3 out of 4 will be polled 1 will be horned. Genetically 1 will be homozygous polled, 2 will be heterozygous polled and the horned one will be homozygous.
- Not all pairs contain a dominate gene. The sex determining gene is one.
- Every egg contains an x chromosome and each sperm contains either an x or y chromosome. If the egg is fertilized by the sperm containing the x we get a female, if it contains the y we get a male.
- Inheritance is not as simple as xyz. Most economically important traits are affected by many different pairs of genes. In the end thousands of pairs of genes will determine the outward appearance of the animal. The environment such as nutrition and disease can influence the expression of those genes.
- Basic systems are Outcrossing, Cross-breeding, and Linecrossing.
- Inbreeding is breeding related animals to increase uniformity. Closebreeding is the mating of closely related animals such as son to dam, sire to daughter, brother to sister. Linebreeding is mating less closely related individuals such as cousins, etc. This system is recommended only for those who are in a position to cull rigidly and can withstand possible losses. Inbreeding is a tool that is useful for identifying superior families and testing for genetic defects.
- Both the environment and genetics can cause congenital birth defects. This is an example of what happens when a parent carrying the undesirable recessive gene, but not exhibiting the trait is mated to one without the recessive gene. The results are 2 of 4 offspring will not carry the undesirable recessive and two will.
- Here’s what happens when the mates both carry the undesirable gene but not the trait. Two out of four of the offspring will be carriers. One will not have the recessive. And one will exhibit the trait.
- More common congenital conditions controlled by genetics.
- Non-congenital defects are those that are not prevalent at birth but appear later as the calf grows.