Download Genetics

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
Mitosis
Meiosis
t
t
t
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