inbreeding, crossbreeding and blood types

What are the consequences of inbreeding in a population?

• Reduction of heterozygosity

• Increases homozygosity (less genetic diversity)

• More likely to show recessive genes

• Animals more likely to “breed true” (produce offspring similar to themselves)

when is inbreeding used

when breeders are actively selecting for a particular characteristic

why are “bad” alleles often recessive

• because dominant lethal alleles are lost through natural selection

Define the relationship coefficient.

The proportion of genes that two individuals have in common as a result of their genetic relationship through a shared common ancestor.

*paths can only connect two individuals related by blood!

define inbreeding coefficient

Predicts the likelihood that an offspring will be homozygous at a given gene locus

steps to calculating inbreeding coefficient

1. Start with animal of interest

2. Find all variations of loops that lead back to that animals

3. For each loop, count the number of nodes (related animals)

4. Inbreeding coefficient is the sum of the contributions of the individual loops

What is inbreeding depression, and why does it occur?

lack of fitness due to breeding among consanguinous (closely related) individuals

• Occurs due to increase in homozygosity and expression of deleterious recessive genes

• Generally manifests as reduced fertility and poor survival of offspring

What should the target inbreeding coefficient be for a prospective mating?

ideally as low as possible

• 5% COI = increase in expression of deleterious recessive mutations

• 10% COI = significant loss of vitality in offspring

what is a backcross

breed offspring to the parent to detect carriers of the recessive genes

consequences of crossbreeding in a population?

• Increases heterozygosity

• May mask recessive genes

• Reduce the likelihood of breeding true

what is crossbreeding

breeding of unrelated individuals

what is heterosis

The opposite of inbreeding depression (hybrid vigour)

• Masking of recessive (deleterious) genes when breeding unrelated individuals

• Offspring are often “fitter”, more likely to survive than parents

what is performance testing for selective breeding

• Is based on phenotype or performance of an animal

• Works best for traits governed by single genes and a dominant allele

examples of performance testing

• Production animals → milk yield, butter fat, carcass yield, meat quality, health, reproductive efficiency

• Performance animals → strength, speed, endurance, conformation, appearance

• Companion animals → size, skill, temperament, appearance, performance

what is progeny testing for selective breeding

Determines carrier status of an animal by examining its offspring

examples of progeny testing

Useful for sex-limited traits (genes for milk yield carried by bulls)

why would molecular testing be used

DNA testing can identify the presence of a deleterious allele

• Can eradicate unwanted alleles from population without culling too many animals

• Only useful for single gene conditions

blood groups in cats

A: antigen A (dominant)

b: antigen B

c: antigen A and B

what type of antibodies do type A cats have

weak anti-B antibodies

what type of antibodies do type B cats have

strong anti-A antibodies

what type of antibodies do type c cats have

none :(, but they have both A and B antigens present on their surface?

Why do cats need to be blood typed before their first transfusion?

Because cats have naturally occurring alloantibodies for the blood type they dont have

most important dog blood types

DEA 1 and DEA 4

Which blood groups are most important in horses?

Aa and Qa

major crossmatch

testing recipient serum with donor cells

• Checking if the recipient has antibodies against donor cells

minor crossmatch

testing recipient cells with donor serum

• Checking if the donor has antibodies against recipient cells

neonatal isoeryhtrolysis

• Offspring is positive for blood group that dam is negative for

• Dam becomes sensitized during first pregnancy and produced antibodies

• Subsequent offspring receive high levels of antibodies in colostrum

• Results in anemia, jaundice, lethargy, tachycardia, tachypnea

most inbred dog breed

Norwegian Lundehund

most inbred horse breed

Clydesdale

natutal selection

individuals with genes best suited to their environment are more likely to survive and pass those genes on to future generations

artificial selection

humans choose which traits/phenotypes they want to reproduce

principles of natural selection

• variation exists within populations

• variation is heritable

• organisms produce more offspring than can survive

• individuals best suited for their habitat survive and reproduce (adaptation)

• populations change overtime (speciation)

why is culling all carriers of deleterious alleles not the best idea

may wipe out the breed or cause genetic bottleneck → inbreeding depression

selection methods

1. performance test

2. progeny testing

3. pedigree analysis/ ancestor evaluation

4. performance test of siblings

5. molecular genetic screening