Week 7 Mating system - inbreeding and crossbreeding

Question 1

What are the mating strategies on animal performance

Answer 1

Random mating

Assortative mating

Question 2

What are the mating strategies based on pedigree relationship

Answer 2

• inbreeding
• linebreeding
• outbreeding
• Crossbreeding

Question 3

What is a random mating

Answer 3

Mating system in which mates are chosen at random. This is done after selecting the best males and females.

Question 4

What is assortative mating

Answer 4

Mated according to their phenotype

There are positive and negative assortative mating

Question 5

What is positive assortative mating

Answer 5

Mate individuals with the similar phenotypes, Mating the best to the best. Worst to the worst

Question 6

What is the effect of positive assortative mating

Answer 6

Increase the amount of variation in the population if we keep both extremes

Question 7

What is negative assortative mating

Answer 7

Mating individual with unlike phenotype.

Mate the best to the worst, can be calling corrective mating and compensatory mating (remove symptoms of one kind.

Question 8

What is inbreeding

Answer 8

Mating of the animals related to each other.

Question 9

What kind of inbreeding stretchiest are there?

Answer 9

Mild inbreeding and intense inbreeding

Question 10

What is mild inbreeding

Answer 10

Involves mating individuals that are not closely related, such as cousins

Question 11

What is intense inbreeding

Answer 11

Mating individuals that are closely related such as sibs, sires and daughters, dams and sons

Question 12

What is the effect of inbreeding

Answer 12

Increase the genotypic frequency

Question 13

What is line inbreeding

Answer 13

Decrease variation within each line

Question 14

What is the phenotypic effect of inbreeding

Answer 14

Uncovers undesirable recessive genes.
-Since inbreeding increases homozygosity, it tends to uncover lethal genes and detrimental genes that have been hidden in the heterozygotes (in the carriers)

Inbreeding tend to see more animals with genetic defects

Question 15

Does inbreeding cause genetic defects

Answer 15

No, it does not create defective genes but uncovers the genes that causes defects that have been hidden in the heterozygotes.
It also uncovers detrimental genes that reduce performance (genes for slow growth)
The phenotypic mean of the population will usually decrease for most traits when inbreeding occurs

Question 16

What is the main issue with inbreeding

Answer 16

Inbreeding depression

Question 17

What is inbreeding depression

Answer 17

The reduction in the population mean that occurs with increase inbreeding.

Reduce performance in fertility.

Question 18

Why use inbreeding

Answer 18

A superior phenotype you want to maintain in the line.
Maintaining a high proportion of the genes of an outstanding ancestor in the herd or flock.

-Inbreeding can also used to help detect and eliminate undesirable recessive genes. (Using sire x daughter mating as a test for undesirable recessive genes .

Increase prepotency

Question 19

What is prepotency

Answer 19

Is the tendency of a parent, most often the sire, to stamp his characteristics on his offspring. It will be more uniform, producing lesser variation of gametes

Question 20

What is the causes of inbreeding depression

Answer 20

If gene action is entirely additive inbreeding will not cause a reduction in the population mean. If the gene is control by the dominant or the epistasis gene, it will not be inherited to the next generation.
As well as overdominance and epistasis

Question 21

What is over dominance

Answer 21

Refers to the situation in which the heterozygotes is superior to either f the homozygotes.

Question 22

What is additive gene,

Answer 22

A phenotype that is express based on two or more genes combination

Question 23

What is epistasis

Answer 23

Depends on maintaining certain favourable combinations of alleles at different loci, inbreeding changes the combination of alleles and case a decline in the population

Question 24

What are the degrees of inbreeding, from the most intense to the lease

Answer 24

• Selfing
• full-sib mating or parent-offsprings mating (most intense form of inbreeding in animals)
• Half-sib, Grandparent-grandoffspringm uncle-niece. (1 generation apart
• Mating of first cousins

Question 25

What is Selfing

Answer 25

Mate a plant to itself

Question 26

How do you know the intensity of inbreeding

Answer 26

Inbreeding coefficient, F. F represents the increase in homozygosity resulting from mating individuals that are more closely related than the average of the population

Question 27

What are the two most common forms of outbreeding

Answer 27

Outcrossing | Crossbreeding

Question 28

What is outcrossing

Answer 28

The mating unrelated individuals within a breed

Question 29

What is Crossbreeding

Answer 29

The mating of animals from different breeds

Question 30

What are the effects of outbreeding

Answer 30

Reduce homozygosity, increase heterozygosity, decrease prepotency (because it decrease the homozygous loci frequency), increase mean population Increases the phenotypic uniformity in the first cross between inbred lines

Question 31

Who uses outcrossing most commonly

Answer 31

Seedstock producers

Question 32

What are the effect of outcrossing

Answer 32

Continually selecting the best available unrelated sires for use in herd has been responsible for most of the changes occurred in breeds of livestock Maintain high levels of performance in herds and flocks Relatively few of the undesirable recessive genes being uncovered

Question 33

Who uses Crossbreeding more commonly

Answer 33

Commercial producers

Question 34

What is a breed

Answer 34

A race of animals within a species that usually have a common origin and similar identifying. Characteristics

Question 35

What are the major reason for Crossbreeding

Answer 35

Breed complementarity Heterosis or hybrid vigor

Question 36

What is breed complementarity

Answer 36

An improvement in the overall performance of crossbred offspring resulting from crossing breed of different but complementary biological types

Question 37

What is heterosis

Answer 37

An increase in the performance of hybrids over that of purebreds, most noticeably in traits like fertility and survivability

Question 38

What does breed complementation involves

Answer 38

Arrays of traits, crossing maternal breed(those excels in maternal traits of fertility, freedom from dystocia, etc) With paternal breed (excel in paternal traits such as rate and efficiency of gain, meat quality etc)

Question 39

How can heterosis be useful?

Answer 39

The crossbreds need to be better than either parental breed

Question 40

What is the heterosis that we get in the crossbred dams called

Answer 40

Maternal heterosis

Question 41

Genetic reasons for heterosis

Answer 41

Dominance - Good traits tend to be dominant and crossbred get the good traits from each breed. Over-dominance - refers to the situation in which the heterozygotes is superior to either of the homozygotes - Crossbreeding increase heterozygosity and the frequency of heterozygotes in the population, therefore the mean of the population will increase. Epistasis - the expression of the genes at one locus depends on the alleles present at one or more other loci. - crossing different breed or lines of animals favourable combinations of genes at different loci may be established( may get favourable epistasis combination of genes)

Question 42

What is the criteria useful for evaluating different Crossbreeding systems

Answer 42

-Merit of component breeds -Hybrid Vigor -Breed complementarity Consistency of performance -Replacement of considerations -Simplicity -Accuracy of genetic predictions

Question 43

What are the crossbreeding system

Answer 43

1. Single cross between 2 breeds 2. Two breeds rotational cross 3. Three breed rotational cross 4. Terminal sire crossbreeding

Question 44

What is Single Cross between 2 Breeds

Answer 44

One type of crossbreeding system simply involves a single cross between two breeds • Mate breed A males to breed B females • For replacement animals, buy outside purebred A males and purebred B females – Do not keep any AB crossbred progeny as replacements

Question 45

The Disadvantages of Single Cross between 2 Breeds

Answer 45

Disadvantages – Whereas this crossbreeding system gives heterosis in the offspring, do not get any maternal heterosis from using crossbred dams – This crossbreeding system only uses 2 breeds, so can not get the good traits from any other breeds – Buying outside animals may increase the probability of introducing diseases into your herd – Dependency on other producers for good animals to bring into your herd.

Question 46

What is Two-Breed Rotational Cross

Answer 46

There are two breeding pastures – Replacement females sired by breed A bulls go into pasture 2 and are mated to breed B bulls for the remainder of their lifetime – Replacement females sired by breed B bulls go into pasture 1 and are mated to breed A bulls for the rest of their lifetime • After a period of time, the calves from cows in pasture 1 will stabilize at about 2/3 breed A and 1/3 breed B – 2/3 of their genes will be derived from breed A and 1/3 will be derived from breed B • Calves in pasture 2 will eventually stabilize at 2/3 breed B and 1/3 breed A – 2/3 of their genes will be derived from breed B and 1/3 will be derived from breed A

Question 47

what is the advantages of Two-Breed Rotational Cross

Answer 47

• The producer can use his own replacement females • Minimizes the possibility of diseases being introduced into the herd – We get maternal heterosis from using crossbred females, as well as heterosis in the progeny – It takes into consideration heterosis for fertility and milk production in the crossbred cow, heterosis for livability of the crossbred calf, and heterosis for growth rate in the calf

Question 48

What is Three-Breed Rotational Cross

Answer 48

• Follows the same pattern as in the two-breed rotational cross, except that a third breed is added • Replacement females sired by breed A bulls go into pasture 2 and are mated to breed B bulls for the rest of their lifetime • Heifers sired by breed B bulls go into pasture 3 and are mated to breed C bulls for the rest of their lifetime • Heifers sired by breed C bulls go into pasture 1 and are mated to breed A bulls for the rest of their lifetime

Question 49

what are the advantages of Three-Breed Rotational Cross

Answer 49

• The producer has complete control over selection and management of replacement females, since he produces his own replacements instead of buying them • Get heterosis in both the crossbred progeny and in the crossbred dams • Gives more maternal heterosis than a two-breed rotation • A three-breed rotation gives 87% as much maternal heterosis as in the F1 female

Question 50

What is Terminal Crossbreeding System

Answer 50

• This system is also called a rota-terminal crossing system • 3 breeding pastures and 3 sire breeds are required • Rotational part of system - Heifers sired by breed A bulls are mated to breed B bulls and vice versa • Terminal cross - older and poorer females from pastures 1 and 2 are taken to pasture 3 where they are mated to breed C bulls and all offspring marketed • The breeds used in the rotational portion of the system should be comparable in size and milk production to minimize difficult births and to stabilise nutrition and management requirements in breeding pastures 1 and 2 • The rotational portion would involve the youngest cows in the herd – the yearling heifers, 2-yr olds, 3-yr olds, and maybe the 4-yr olds • Cows are not mated to the terminal sire breed until they are 4-yr-old or older when there is less likelihood of calving difficulty • The terminal sire breed would be one that has good growth and carcass traits, since all of the progeny from the terminal cross are marketed

Question 51

Why are heifers from the terminal sire breed not kept as replacement for Terminal Crossbreeding System

Answer 51

because they are larger in size, have higher energy requirements, and require more feed. Also, they are out of the older and poorer cows

Question 52

What happen to Steers and poorer heifers for terminal crossbreeding system

Answer 52

not kept for replacements would also be marketed from | the rotational portion of the system

Question 53

What are the advantages for Terminal Crossbreeding System

Answer 53

• This system allows the producer to produce all of his own replacement females • It uses crossbred dams • Get individual heterosis in the crossbred offspring and maternal heterosis from the crossbred mothers • This system allows us to take advantage of size complementarity, we can mate smaller dams to a larger breed of sire – This system allows us to utilize heterosis, breed complementation, and size complementarity

Question 54

Crossbreeding Systems in Practice

Answer 54

* Modifications or combinations of one or more of these systems will probably be necessary to fit each individual operation in terms of facilities, management, labour availability, and market * A long-term plan should be well thought out before starting a crossbreeding program, crossbreeding will often require more labour and management decisions * Crossbreeding is not a cure for poor management and unproductive animals * Selection of breeding males and females is just as important as in any other breeding program * In order to maximize the performance of the animals in our herd or flock, we need to use selection in conjunction with crossbreeding