Genetics

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Genetics
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Genetics

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

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Father of Genetics

• Gregor Mendel
• Austrian monk
• did experiments with peas and proved that certain
  characteristics..

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.

• Such as color and height, are passed from parent
  to offspring

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Differences

• all differences in organisms are not caused by
  genetics
• some are caused by the environment
• the conditions under which the animals are raised

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Parts of the cell

• cell membrane - contains the cytoplasm and the
  nucleus

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Cytoplasm

• protects and cushions the nucleus

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Nucleus

• contains the genetic material

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Chromosomes

• carry the genes
• exist in pairs in all cells except sperm and egg
  cells

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Genes

• single determiner of a hereditary trait

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Cell Division

• two types
• Mitosis
• Meiosis

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Mitosis

• cell division for growth
• this division never ends
• chromosome pairs are duplicated exactly alike

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Mitosis

• each new cell is exactly like the old ones
• asexual division
• chromosomes are in pairs

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Mitosis

• steps of mitosis
• Prophase (Interphase)
• Metaphase
• Anaphase

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Steps

• Telophase
• Cytokinesis
• PMATC

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Meiosis

• cell division of reproductive cells (sperm and
  egg)
• each new cell is not exactly like the old one

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Meiosis

• in each new cell chromosomes are not in pairs
• each new cell contains half of the original
  number of chromosomes

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Meiosis

• allows for random assortment of parental genes

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Gamete

• mature egg or sperm cell
• each gamete has half the original number of
  chromosomes

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Dominant gene

• in a pair, hides the effect of another gene

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Recessive gene

• the gene which is hidden by a dominant gene

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Examples

• of dominant genes
• tongue rolling
• free ear lobes
• polled cattle

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Examples

• of recessive genes
• color red in Holsteins
• dwarfism

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Symbols

• dominant genes
• capital letters

A
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Symbols

• recessive genes
• lower case letters

a
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Homozygous

• gene pairs
• one which carries two genes for a trait
• both represented by capital or lower case letters

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Homozygous

• polled - PP
• horned - pp

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Heterozygous

• gene pairs
• one which carries one dominant and one recessive
  gene

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Heterozygous

• Pp

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Genotype

• genetic makeup of an animal or a given trait
  expressed by symbols
• Ex PP, AA, Pp, Aa, aa

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Phenotype

• physical appearance expressed in words
• Ex polled, horned

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Mitosis
T t
Meiosis
T
t
Mitosis
t
t
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Steps of Meiosis

• Prophase I ( Interphase)
• Metaphase I
• Anaphase I
• Telophase I

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Steps of Meiosis

• Prophase II (Interphase)
• Metaphase II
• Anaphase II
• Telophase II
• Cytokinesis

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If

• two heterozygous animals are mated
• the number of traits being selected is six
• the total number of offspring is over 16,000,000

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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

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Incomplete Dominance

• Roan coloring in cattle
• RR X WW RW
• Red X White Roan
• Roan - mixture of red and white hairs

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Sex determination

• male sex chromosomes
• male mammals have two different sex chromosomes
• XY
• females are XX

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Sex determination

• poultry
• the female determines the sex of the offspring
• female is ZW
• male is ZZ

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Sex Linked Traits

• genes which are carried only on the sex
  chromosomes
• ex red green color blindness
• 225 males
• 1150 females

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Sex Linked Traits

• hemophilia
• bleeders disease
• more common in males than in females

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Sex Linked Traits

• barred feather pattern vs black in chickens

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Mutation

• when a new trait is shown that did not exist in
  either parent

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Mutation

• the new breed of polled Herefords
• which resulted from the crossing of two horned
  animals

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Causes of Mutations

• radiation (nuclear accident or x-ray)
• chemicals

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Systems of breeding

• purebreeding
• inbreeding
• outcrossing
• grading up
• crossbreeding

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Purebreeding

• purebred is defined as a member of a breed
• the animals of which possess a common ancestry
• distinctive characteristics

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Purebreeding

• is registered or eligible for registry

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Outcrossing

• mating of animals of different families within
  the same breed
• relatively safe system of breeding

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Outcrossing

• unlikely that two unrelated animals would carry
  the same undesirable genes and pass them on

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Grading up

• mating of purebred sires to grade females
• relatively inexpensive and is dependent upon the
  quality of the sire

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Inbreeding

• mating of related animals
• closebreeding - a form of inbreeding
• most intensive form
• animals are very closely related

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Closebreeding

• sire to daughter
• son to dam
• brother to sister

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Closebreeding

• was used on foundations but is not used much
  today
• used in the development of the Quarter Horse breed

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Closebreeding

• animals are more uniform
• more chance for undesirable recessive gene
  expression

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Linebreeding

• refers to the mating of animals which are more
  distantly related
• cousins, grandparents, half sibling

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Linebreeding

• used favorably today because there is less chance
  of expression on undesirable recessive traits

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Linebreeding

• less chance of genetically superior stock
• considered middle of the road

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Crossbreeding

• mating of animals from different breeds
• often causes hybrid vigor

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Hybrid Vigor

• causes crossbreds to outproduce the average of
  their parents
• some breeds cause hybrid vigor better than others

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Hybrid Vigor

• breeding a British breed, Angus, to an Indian
  Breedlt Brahman
• compared to an Angus X Shorthorn cross

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Hybrid Vigor

• Angus X Brahman would have more hybrid vigor

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Selection

• based upon
• type
• pedigree
• showring winnings
• production records