Genetics. the study of heredity the way in which traits of parents are passed on to offspring.
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Transcript of Genetics. the study of heredity the way in which traits of parents are passed on to offspring.
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