Please I need someone to help me in this

1

Introduction to Animal Genetics

Animal Sciences 121

Origins of the Science of Genetics

Earliest Theories

Pangenesis

Hippocrates and Aristotle, The organism formed through sexual reproduction “substance” from the egg and “form” from the seminal fluid. Sperm and Egg from all parts of the body

each giving its own traits

Accepted by many scientists into late 19th Cent

(including Charles Darwin)

Darwin’s Idea

Origins of the Science of Genetics

Earliest Theories Preformationism

1694 Nicolaas Hartsoeker

Postulated the theory of

“Homunculi”

Completely formed miniature individual inside sperm and egg cells (he never claimed to have actually seen these ‘little men”)

Origins of the Science of Genetics

Earliest Theories Acquired Characteristics

Jean Baptist de Lamark 1800s

Use or disuse of organs, limbs, other controlled whether they were passed to offspring

Related to Pangensis

2

Earliest Theories Germplasm

late 1800s August Weismann Sex cells are fundamentally different than

body cells – somatoplasm 1st major scientific challenge to Pangenesis

Mouse tails – cut off – offspring had normal tails

Origins of the Science of Genetics

Genetics, as the study of heredity and its application to animal agriculture, had its practical origin in peas.

Born 1822, Czech Republic

Augustinian friar 1856 began experiments, results presented to the

Brünn Society for National History in 1865,

and published, 1866.

Gregor Johann Mendel

Mendel’s Pea Plant Traits

3:1

3

Mendel’s Laws

Segregation –

Each trait has two possibilities which pass to offspring in a random but predictable way 9:3:3:1

Mendel’s Laws

Independent Assortment –

Different traits are passed to offspring without regard any other trait

Mendel’s Laws

Forgotten till ~1900

Hugo de Vries – Holland

Carl Correns – Germany

Erich von Tschermak – Austria

Re-Discovered Mendel’s Work

35 years after publication

4

Mendel’s Findings Applicable to Animals

William Bateson – England

Lucien Cuenot – France

William Castle - US

Genetics Terms

Genetic Material-

DNA deoxyribonucleic acid

Chemical polymer,

Nitrogen Base, Sugar, and Phosphoric acid -- Nucleotide

Unit of heredity-

Gene

Section of DNA

Watson and Crick 1953 (1962) Maurice Wilkins Rosalind Franklin

DNA Structure Double Helix

Purines Adenosine (A)

Guanine (G)

Pyrimidines Cytosine (C)

Thymine (T)

James Francis Maurice Rosalind Watson Crick Wilkins Franklin

Nobel Prize 1962 RIP 1958

5

Location of the genes

Chromosomes

Cell Nucleus

All cells

ChromosomesChromosomes are the packaging for DNA

Number of chromosomes in an animal’s cell

6

Chromosomes are the packaging for DNA

Is an animal’s physical size related to the number of chromosomes it contains?

Horse > Human > Mouse

NO

Examples of Chromosome Numbers*

*Chromosomes occur in pairs

Drosophlia, Fruit Fly 8 Pig 38 Mouse 40 Sheep 54 Cattle 60 Horse 64 Dog 78 Chicken 78 Fish 22 to 150

Organized in pairs, e.g. Swine = 19

Livestock are genetically diploid

= 2 copies of each chromosome

identical

except for the sex

chromosomes (X+Y),

non-identical

Chromosomes

Swine Karyotype

2N=38

Since Genes Reside on Chromosomes

How are genes transmitted from parents to offspring

while maintaining a constant number of chromosomes ?

7

Cell Cycle Somatic Cells 2N 2N

http://media.oregonstate.edu/media/0_plh9mfoh

•http://media.oregonstate.edu

/media//0_plh9mfoh

Active DNA Making Protein

DNA Duplicates 2X normal DNA

2N 4N

Most of cell life in this phase

Gradual condensing of DNA

Chromosomes appear as 2 strands joined in the middle

Nuclear membrane begins to breakdown

Nuclear membrane gone

Chromosomes free in cytoplasm

Centromere attached to microtubule

Chromosomes line up in middle Metaphase plate

8

Chromosomes separate at the centromere

Each chromosome half moves to an opposite pole

Cell Divides Nuclear Membranes form Surrounding Chromosomes

4N 2N

Cell division video

https://www.youtube.com/watch?v=9A3jZYnzlpQ

Germ Cells

Meiosis

2N 1N

•http://media.oregonstate.edu/m

edia//0_unpleanx

DNA duplicates 2N 4N

Chromosomes pair-up Crossing over occurs

9

Chromosome pairs separate

Genetic material halved 4N 2N

Reduction Division

The Fundamental Difference

Chromosomes split at centromere “Normal Division” with half the number of Chromosomes 2N 1N

Equational Division

Each spermatid has ½ the genetic material

Ovum same divisions

Polar bodies lost

Meiosis

https://www.youtube.com/watch?v=6xMXKU7JnMQ

How does the gene express itself ?

10

DNA mRNA

mRNA Protein

Universal

Code

Terminology

Autosomes, non sex-chromosomes

Locus, gene site on the chromosome

Alleles, forms of a gene that can occupy a locus

Homozygous versus Heterozygous (Similar AA vs Dissimilar Aa)

Allelic Interactions -Complete Dominance (B&R cattle)

- Co-Dominance (Roan Cattle)

- Incomplete Dominance (Creeper Chickens)

Polled vs horns in Cattle - Complete Dominance

Parents (P): Polled (PP) x horned (pp)

Gametes: P p

F1 (progeny): Pp

Polled

11

Mating: Pp x Pp (both Polled)

Gametes produced

Pp x Pp

Sperm: P or p Egg: P or p The probability of sperm or egg containing p or P is 50 %

Probability in zygote of pp is 1/2 (50%) x 1/2 = 25%, etc

Punnett Square

P p

Complete P PP Pp

Dominance p Pp pp

1PP 2Pp 1pp

(25%) (50%) (25%)

75% Polled 25% Horned

Specie Dominant Recessive

Cattle Black hair coat Red hair coat

Chicken Rose comb Single comb

Horse Black hair coat Chestnut or sorrel

Sheep Hairy fleece Wooly fleece

Swine (Hamps.) Black hair Red hair

Dog Wire hair Smooth hair

Cat Short hair Long hair

Examples of Complete Dominance (/Recessive Traits) in Selected Domestic Animals

Co-Dominance

(Roan Cattle)

Red (RR) White (rr)

X

Roan (Rr)

12

Punnett Square

R r

Co-Dominance R RR Rr

r Rr rr

1RR 2Rr 1rr

(25% Red) (50% Roan) (25% White)

(Shows both traits)

Incomplete Dominance

Creeper Chicken

Cpcp Cpcp

X

Punnett Square

Cp cp

Incomplete Cp CpCp Cpcp

Dominance cp Cpcp cpcp

1CpCp 2CPcp 1cpcp

(25% Lethal) (50% Creeper) (25% Normal)

X

(Intermediate type)

Allelic Interactions are the same for all species of

animals…….

Complete Dominance (Either trait expressed)

Co-Dominance (Both traits expressed)

Incomplete Dominance (Intermediate type)

13

Sex Determination

Swine Karyotype

2N=38

Paired set of unequal chromosomes

Sex-linkage

Sex-linked- a gene located on the sex chromosome.

Heterogametic Sex two types of gametes based on sex chromos

Mammals (XY): male Birds (Zw): female

Homogametic Sex

one type of gamete based on sex chromos

Mammals (XX): female Birds ZZ: male

Single Locus Traits

Traits controlled by 1 gene locus

Traits are discrete – Black or Red hair color

Changes in the phenotype of a group (herd, flock) of animals is relatively

easy to accomplish (Black haired cattle to red haired).

Quantitative Traits

Traits controlled by many gene loci (n = 10, 20, 30 +)

growth rate

feed efficiency

milk production

litter size

racing speed

Economic Traits

14

Selection of Quantitative Traits Animal Breeding

Genetic improvement of Livestock

Selective Breeding

Pedigree

Jacob’s lamb

Breeding Strategies Purebred - pedigreed animals within a breed; specific

requirements;

Crossbreeding – mating individuals from different breeds

Inbreeding - mating of closely related individuals;

Outcrossing - mating different families within a breed

Line Crossing - mating of a purebreds of dissimilar lines within the breed

(form of outcrossing)

Cross Breeding Mating of dissimilar breeds

heterosis /hybrid vigor

Usually for market animals

Cannot predict the results

15

Heterosis or Hybrid Vigor

(Ave. Crossbreds - Ave. Purebred)

% Heterosis = ___________________________ x 100 %

Ave. Purebred

Average Weaning Wt., Breed A = 448 lbs

Average Weaning Wt., Breed B = 460 lbs

Average Weaning Wt., Crossbreds (AB) = 475 lbs

Heterosis = 4.6%