GENETICS - 13 IMPROVEMENT & CONTROL OF TRAITS *incomplete*

inherited

To genetically control animal traits as we as disorders, one must first determine if they are __.

positive, affected, common

If genes make any contribution to the etiology of a disorder, it follows that there will be a __ relationship between the chance of an individual being __ and the extent to which that individual has genes in __ with affected individuals.

genes

Members of the same family have more __ in common than members of different breeds.

1. autosomal dominant

2. autosomal recessive

3. X-linked dominant

4. X-link recessive

Mendelian types of Inheritance:

Autosomal dominant

• Transmitted from generation to generation without skipping

• Every affected offspring has at least one affected parent, except for new mutants

• Normal offspring from affected parents produce normal offspring when mated to normals

• Approx. equal number of males and females are affected

Autosomal recessive

• Inheritance of a disorder may skip generations

• All offspring of two affected parents are affected

• Approx. equal number of males and females affected

• Carriers who mate with homozygous normals produce ½ carriers among their offspring

• In mating between affected parents (Aa x Aa), the segregation frequency is ¼

• Mating between an affected parent and unrelated normal will produce only normal offspring

• The greater the genetic relationship, the more likely they are carriers of the same mutant gene

X-linked dominant

• Affected males when mated to normal females transmit the disorder to all their daughters but none to their sons

• if common: affected females mates with normal males transmit disorder to an avg. of ½ of their sons and ½ of their daughters

• if rare: its incidence in female is approx. twice than in males

• every affected offspring has at least one affected parent, except in new mutants

X-linked recessive

• Inheritance of a disorder may skip generations

• All offspring of two affected parents are affected

• Incidence in females is approx. the square of the incidence in males (lower in females)

• if rare

  • most affected individuals are males and results from mating among normal parents

  • segregation frequency is 0 in females and ½ in males

  • affected males when mated to normal unrelated females transmit to none of their offspring, but all daughters are carriers

  • affected females when mates to normal males transmit the disorder to all their sons and none to daughters, but daughters are carriers

1. Genetic variation

2. Selection of highly heritable traits

3. Accurate measurement and recording

4. Proper mating or breeding systems

Genetic Improvement by Selection:

1. Independent culling method

2. Tandem method

3. Selection index

Methods of Selection for More than One Trait:

net value, economic

The __ of an animal depends on several traits that may not be of equal __value or may be independent of each other.

select

It is usually necessary to __ for more than one trait at a time, the desired trait usually of economic value.

Pleiotropy

Genetic correlation exists when genes affect one trait also affect another trait.

Independent culling method

• practiced for only one trait at a time until satisfactory improvement has been made in this trait

• efforts are then directed toward the improvement of a second trait, then the third trait, and so on.

• if there is desirable genetic association between the traits, improving one trait results in the improvement of the trait not selected for

• if there is little genetic associated between traits, the improvement would be less efficient

Tandem method

• may be practiced for two or more traits at a time

• a minimum standard is set that an animal must meet in order to be saved for breeding purposes

• failure to meet standard results in rejection of the animal

• this method is disadvantageous because some very genetically superior animals may be rejected for not meeting the minimum standards for the traits selected for

Selection index

• involves separate determination of the value for each traits selected fir

• the addition of these values gives a total score for all the traits

• animals with the highest total scores are kept for breeding purposes

• this method is more efficient than tandem because it allows the superior individuals (in some traits) to be saved for breeding purposes even though they are slightly deficient in some of the traits

• the influence of each trait on the final index is determined by how much weight that trait is given in relation to other traits

• the weight depends on the following

  • relative economic value

  • heritability of each trait

  • genetic association among traits

1. Inbreeding

2. Outbreeding

Animal Breeding/Mating Systems:

Inbreeding

Mating of animals that are closely related or more alike, resulting in progenies that are more homozygous than their parents.

Outbreeding

Mating of animals that are less alike or less closely related, resulting in progenies that are more heterozygous than their parents.

Relationship

Proportion of identical genes that two animal have because they are members of the same family.

Inbreeding Coefficient

Is the probability that the two genes present at a locus in that individual are identical by descent.

Direct Relationship

• Exists between individuals and ancestors, and between individuals and descendants

• An individual is related to a parent because ½ of that individual’s genes were obtained from the parent

one-half

An offspring has exactly __ of its genes in common with each of its parents.

Relationship

Between two non inbred individuals is the expected proportion of genes that the two have in common.

1/2

Relationship between offspring and parent is _.

1/4

Relationship between offspring and grandparent is _.

1/8

Relationship between offspring and great-grandparent is _.

(1/2)^n

• Relationship between an individual and ancestor decreases by ½ for each generation that separates the individual from that ancestor.

• N is the number of generations between the individual and ancestor in the direct pathway of direct descent from the ancestor to the individual.

I GIVE UP (*incomplete*)

Ayoko na..