Department of Natural Sciences Inheritance of Characteristics and Breeding in Animals NSCI3770 Introduction to Animal Husbandry. CAC.

Department of Natural Sciences

Inheritance of Characteristics and Breeding in Animals

NSCI3770 Introduction to Animal Husbandry. CAC.

2

• Introduction, some videos, discussion

• Basics of cell division, growth and gamete production

• Genetics, basic ideas and a tutorial exercise

• Examples of inherited genetic disorders

In this session…

3

• After viewing the first video discuss:– What was the video about?– Why do breeders do this?– What are the welfare implications of this practice?

Starter video and discussion:

4

GENETICSSection 1

• Two types of cell division in cells– Mitosis

• growth and repair of tissues in all body cells• involves replication and division from one cell to form two identical cells

– Meiosis• Prior to sexual reproduction – only in ovaries & testes.• Produces male and female gametes (eggs & sperm)• Chromosome numbers are halved

Types of Cell Division

6

• Made of DNA

• Carry genes which are information to build parts of the animal’s body

What do we know about chromosomes?

• Diploid (2n) The normal state.– The full complement of chromosomes in body cells.– Two of each chromosome (one inherited from father & one from the

mother)– Mitosis maintains the diploid state when cells divide for growth & repair

of tissues.

• Haploid (n) Only in ‘gametes’ (egg & sperm)– Half the number of chromosomes. Only one of each chromosome– Produced ONLY in reproductive cells when Meiosis produces the

haploid egg and sperm.

Number of chromosomes

• Mitosis

• Meiosis

Videos

· Mitosis· Division of the nucleus· Results in the formation of two identical

‘daughter’ nuclei with diploid chromosomes (2n)

· The way body cells divide for growth & repair

Mitosis

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Stages of Mitosis

Duplication

Single chromatids

· Interphase

· No cell division occurs

· The cell carries out normal metabolic activity and growth

· Synthesis (S) phase, chromosomes duplicate

· Prophase

· First part of cell division

· Centromeres migrate to the poles

S(DNA synthesis)

G1

G2

Cytokinesis

Mito

sis

INTERPHASE

MITOTICPHASE (M)

11

Chromosome duplication

Centromere

Chromosomeduplication

Sister chromatids

Chromosomedistribution

todaughter

cells

Stages of Mitosis

Centrosomes(with centriole pairs) Kinetochore

Early mitoticspindle

Chromatin

INTERPHASE PROMETAPHASEPROPHASE

Centrosome Fragmentsof nuclearenvelope

Plasmamembrane

Chromosome, consistingof two sister chromatids

Nuclearenvelope

Spindlemicrotubules

Nucleolus

Centromere

Stages of Mitosis

Metaphaseplate

Nucleolusforming

METAPHASE TELOPHASE AND CYTOKINESISANAPHASE

Cleavagefurrow

Daughterchromosomes

NuclearenvelopeformingSpindle

• Metaphase

– Chromosomes line up‘in single file’on the spindle

Stages of MitosisSister chromatids

Centromere

· Anaphase

· chromatids separate & are pulled toward the poles

· Telophase

· Daughter nuclei begin forming. Each new cell has a chromatid from each original chromosome. (These will make a new copy before the next cell division)

· Cell begins to divide

Meiosis (halves the number of chromosomes)

• Only occurs in ovaries & testes to produce eggs & sperm (gametes)

• Chromosomes line up ‘in pairs’ on spindle (4 chromosomes)

• One chromosome from each pair moves to each end of the cell

• The 2 new cells have half the number of chromosomes (2)

• These new cells divide again by mitosis to separate the chromatids. (4 haploid gametes)

17

SELECTING ANIMALS FOR BREEDING

• Genotype – Description of actual forms of a gene (alleles) present in the individual. (e.g. BB/Bb/bb in the rabbit example)

• Phenotype – the appearance of the animal as a result of genes inherited– physical characteristics e.g. coat colour – Metabolic characteristics e.g. blood clotting– behaviours can also be an expression of the inherited genes.

Select breeding animals

• Alleles - – the alternative forms of a gene at the same locus on paired

chromosomes. – Homozygous - both alleles exactly alike– Heterozygous - both alleles different

• Dominant – some alleles are dominant over others and will ‘mask’ the recessive

gene. E.g. brown eyes are dominant over blue eyes.

• Recessive – These characteristic only show up when both alleles inherited are

recessive. E.g. blue eyes.

• Humans select animals for and against some physical characteristics.

– breed standards for the competition ring– ‘good looks’– inheritable diseases eg hip dysplasia– neotony (breeds that retain ‘infantile’ characteristics – e.g. big eyes,

short, flat muzzle)• think pugs, pekes and persians

– ease of care• short haired varieties• people friendly characteristics

– ragdolls

• Humans select animals for and against some behaviours

– For those that ensure survival and easy care

• easy birthing and good mothering• animals with high libido

– For those that increase suitability for intended use• highly trainable for competition / work• low aggression for family pets

– Against those that are socially unacceptable • breeding aggressive bitches and producing aggressive pups

• Inbreeding– breeding together animals that are closely related eg brother- sister,

father - daughter.– Usually done to produce animals that are homozygous for desirable

characteristics

• Line breeding (is a form of inbreeding)– breeding related individuals, less closely related eg cousins, grandsire

- grandchild– again to breed for desirable characteristics

• Outbreeding– breeding animals with no relationship. Hybrid vigour.

Types of breeding

• Can you guarantee homes?

• Do you have room for a litter?

• Can you afford to?– Stud fee– feeding mother– feeding young– preventative health care

• Do you have appropriate breeding animals?

• Are you experienced enough to choose good animals for mating?

Breeding, should I or shouldn’t I?

Choosing an appropriate breeding animal

• Ethics

• Pedigree

• Physical assessments– general health and

soundness– hip scores (dogs)– elbow scores (dogs)– eye tests (typically

golden retrievers)

– FIV (cats)– FeLV (cats)– other breed specific

issues

• Behavioural assessments– temperament tests

• Breed society requirements

• Age

• Health

Predicting the likely OffspringPunnet Squares

27

• Each gene may have 2 or more forms called alleles

• E.g. these may be black or white in a rabbit

Alleles

• If coat colour in rabbits is – dominant for black (B)– & recessive for white (b)– what are the phenotype

(colour) of the following? Hint, we see the dominant allele

Try This

Bbbb

BB

Monohybrid Cross

Black hair is dominant, white is recessive

Genotype & Phenotype?

bb BB

ResultParents BB X bb

Gametes B B b b

Offspring Bb Bb Bb Bb

(F1)

Result 100% Bb, 100% Black

b

B

b

B

Doe

Buck

Bb Bb

Bb Bb

ParentsDoe Buck

Phenotype: All Black

Genotype: 100% Bb (heterozygous)

bb BB

Phenotype: 3 Black : 1 white

Genotype: 25% BB : 50% Bb : 25% bb

ParentsB

B

b

b

Doe Buck

Doe

Buck

BB Bb

Bb bb

Bb Bb

33

• Work in pairs

• Each person needs a coin

• Use heads for the dominant black allele (B)

• Use tails for the recessive white allele (b)

• Each pair should toss one coin each to represent the random selection of alleles from the heterozygous parents (Bb) to create a new ‘rabbit’

• Do this 8 times, class results scored

Let’s try an experiment

Phenotype: 50% Black, 50% White

Genotype: 50% Bb : 50% bb

b

B

b

b

Doe

Buck

Bb Bb

bb bb

Bbbb

ParentsDoe Buck

• Female: a pair of large X chromosomes (XX)

• Male: one large X like female and one small Y chromosome (XY)

• Sex-linkage: Loci which are located on the sex chromosome => sex-linked. g. colour blindness in males

Sex Chromosomes

Sex Determination

Parents: Sire x Dam

Chromosomes: XY XX

segregation segregation

Germ Cells: X Y X X(gametes)

Offspring: XX XX XY XY(zygotes)

Sexes: Females Males

Quiz - Definitions What do the following terms mean?

• Chromosome

• Gene

• Allele

• Dominant

• Recessive

• Homozygous

• Heterozygous

• Phenotype

• Genotype

• Gamete– What kind of cell division forms

them?– Where does this occur?– What are the two kinds?

• Zygote– What kind of cell division will take

place as this divides & grows into a foetus?

• Sex Linked characters

Inherited problems

• Cats– Manx – no tail– Folded ears– Polydactyl –xtra toes– Deafness- white, blue

eyes.

• Dogs– Haemophilia– Collie eye– Progressive Retinal

Atrophy– Hip/Elbow dysplasia

HIP DYSPLASIA• Progressive deformity of hip

joints

• First 12 motnhs

• Shallow ‘ball and socket’ joints

• Partially dislocate-instability

• Osteoarthritis

• PAIN

Hip Dysplasia• Inherited condition

• Other factors can be involved– Nutrition imbalance/

overfeeding– Exercise, overexercise,

jumping– trauma

• Lameness under 1 year if severe

• Affected by weight and exercise

• Reluctant to jump/mount stairs

• Stiffness on rising

• Permanent hind leg lameness

CLINICAL SIGNS

• Scored on joint depth and osteoarthritic change– Total score = sum of 9 separate scores of various features on both hip

joints

• Average hip score varies by breed

• The following are particularly susceptible:– German shepherd. Giant schnauzer gordon setter, rottweiller,

samoyed tibetan terrier, newfoundland, blood hound, bullmastiff, St Bernard, welsh springer spaniel

BREED SUSCEPTABILITY

• Selectively breed only from dogs with good hip joints will decrease the disease incidience

• Alleviate pain and suffering

AIM of SCORING

ELBOW DYSPLASIA

• A number of different conditions impairing the function of the elbow joint:– Labradors & Golden retrievers– German shepherds

• Strong hereditary base

• Masked in heterozygous animals

• Forelimb lameness between 4-12months

• Older dogs become lame with x-rays showing Osteoarthritis

• Sound breeding dogs but produce pups with Elbow Dysplasia

• Phenotype not always = genotype

CLINICAL SIGNS

• Minimize pain and slow development

• Limit exercise , weight control, pentoson, nsaid, glucosamine chondroitin

• Surgery

• Still likely to lead to arthritis

TREATMENT

• A congenital fissure in the roof of the mouth forming a communication between the nasal passages and the oral cavity.

• Found in various breeds especially brachycephalics and Siamese cats.

• Inherited as a recessive trait in English Bulldogs.

• Can be caused by hypervitaminosis A, corticosteroids, griseofulvin

Cleft Palate

• Failure of clotting mechanism in blood

• At least 9 different types due to different abnormalities in the chain of events leading to clotting

• Most common forms sex linked.

• Von Willebrand’s Disease• Most common inherited bleeding disorder in dogs• Deficient in clotting Factor VIIIR• Inherited esp Dobermans. Himalayan cats.

• Haemophilia A• Deficient in clotting Factor VIII• Inherited in a number of dog breeds

BLEEDING DISORDERS

50

• http://www.ufaw.org.uk/geneticwelfareproblems.php

Check your breed issues

52

This powerpoint used material from Diane Fraser (Unitec) who previously taught this section.

Picture sources (most drawings are from this text or earlier versions):

Campbell, N.A., Reece, J.B., and Simon, E.J. (2006) Biology: Concepts and Connections. San Francisco: Benjamin Cummings

References and acknowledgements