Genetics

Genetics• the study of heredity

• the way in which traits of parents are passed on to offspring

Father of Genetics• Gregor Mendel

• Austrian monk

• did experiments with peas and proved that certain characteristics……..

……….• Such as color and height, are

passed from parent to offspring

Differences• all differences in organisms are

not caused by genetics

• some are caused by the environment

• the conditions under which the animals are raised

Parts of the cell• cell membrane - contains the

cytoplasm and the nucleus

Cytoplasm• protects and cushions the

nucleus

Nucleus• contains the genetic material

Chromosomes• carry the genes

• exist in pairs in all cells except sperm and egg cells

Genes• single determiner of a

hereditary trait

Cell Division• two types

• Mitosis

• Meiosis

Mitosis• cell division for growth

• this division never ends

• chromosome pairs are duplicated exactly alike

Mitosis• each new cell is exactly like

the old ones

• asexual division

• chromosomes are in pairs

Mitosis• steps of mitosis

• Prophase (Interphase)

• Metaphase

• Anaphase

Steps• Telophase

• Cytokinesis

• ** PMATC

Meiosis• cell division of reproductive

cells (sperm and egg)

• each new cell is not exactly like the old one

Meiosis• in each new cell

chromosomes are not in pairs

• each new cell contains half of the original number of chromosomes

Meiosis• allows for random

assortment of parental genes

Gamete• mature egg or sperm cell

• each gamete has half the original number of chromosomes

Dominant gene• in a pair, hides the effect of

another gene

Recessive gene• the gene which is hidden by

a dominant gene

Examples• of dominant genes

• tongue rolling

• free ear lobes

• polled cattle

Examples• of recessive genes

• color red in Holsteins

• dwarfism

Symbols• dominant genes

• capital letters

Symbols• recessive genes

• lower case letters

Homozygous• gene pairs

• one which carries two genes for a trait

• both represented by capital or lower case letters

Homozygous• polled - PP

• horned - pp

Heterozygous• gene pairs

• one which carries one dominant and one recessive gene

Heterozygous• Pp

Genotype• genetic makeup of an animal

or a given trait expressed by symbols

• Ex: PP, AA, Pp, Aa, aa

Phenotype• physical appearance

expressed in words

• Ex: polled, horned

T t

T t

t t

Meiosis

Mitosis

Mitosis

Steps of Meiosis• Prophase I ( Interphase)

• Metaphase I

• Anaphase I

• Telophase I

Steps of Meiosis• Prophase II (Interphase)

• Metaphase II

• Anaphase II

• Telophase II

• Cytokinesis

If• two heterozygous animals are

mated

• the number of traits being selected is six

• the total number of offspring is over 16,000,000

Incomplete Dominance

• when one gene does not hide the effect of the other in a gene pair

• result is a mixture of the two traits

Incomplete Dominance

• Roan coloring in cattle

• RR X WW = RW

• Red X White = Roan

• Roan - mixture of red and white hairs

Sex determination• male sex chromosomes

• male mammals have two different sex chromosomes

• XY

• females are XX

Sex determination• poultry

• the female determines the sex of the offspring

• female is ZW

• male is ZZ

Sex Linked Traits• genes which are carried only

on the sex chromosomes

• ex: red green color blindness

• 2:25 males

• 1:150 females

Sex Linked Traits• hemophilia

• bleeders’ disease

• more common in males than in females

Sex Linked Traits• barred feather pattern vs

black in chickens

Mutation• when a new trait is shown

that did not exist in either parent

Mutation• the new breed of polled

Herefords

• which resulted from the crossing of two horned animals

Causes of Mutations• radiation (nuclear accident or

x-ray)

• chemicals

Systems of breeding• purebreeding

• inbreeding

• outcrossing

• grading up

• crossbreeding

Purebreeding• purebred is defined as a

member of a breed

• the animals of which possess a common ancestry

• distinctive characteristics

Purebreeding• is registered or eligible for

registry

Outcrossing• mating of animals of different

families within the same breed

• relatively safe system of breeding

Outcrossing• unlikely that two unrelated

animals would carry the same undesirable genes and pass them on

Grading up• mating of purebred sires to

grade females

• relatively inexpensive and is dependent upon the quality of the sire

Inbreeding• mating of related animals• closebreeding - a form of

inbreeding • most intensive form• animals are very closely related

Closebreeding• sire to daughter

• son to dam

• brother to sister

Closebreeding• was used on foundations but

is not used much today

• used in the development of the Quarter Horse breed

Closebreeding• animals are more uniform

• more chance for undesirable recessive gene expression

Linebreeding• refers to the mating of

animals which are more distantly related

• cousins, grandparents, half sibling

Linebreeding• used favorably today because

there is less chance of expression on undesirable recessive traits

Linebreeding• less chance of genetically

superior stock

• considered middle of the road

Crossbreeding• mating of animals from

different breeds

• often causes hybrid vigor

Hybrid Vigor• causes crossbreds to

outproduce the average of their parents

• some breeds cause hybrid vigor better than others

Hybrid Vigor• breeding a British breed,

Angus, to an Indian Breed< Brahman

• compared to an Angus X Shorthorn cross

Hybrid Vigor• Angus X Brahman would

have more hybrid vigor

Selection• based upon

• type

• pedigree

• showring winnings

• production records