SPECIFIC OBJECTIVES AND
COMPETENCIES
Genetics & Heredity
530-F
I.
Terms and definitions
A. Gene
Gene---Complex
Complex molecule that determines hereditary
characteristics of living animals; located at definite
places on the chromosomes
B. Chromosome
Chromosome---Thread
Thread--like structure which exists in
pairs and carries genes
C. Mutation
Mutation---Random
Random changes that take place in a gene
(Note: These are very rare and may be lethal.)
D. Mitosis
Mitosis---Division
Division of a body cell into two duplicate
body cells
E Meiosis
E.
Meiosis---Division
Division of a sex cell producing a cell or
cells containing only one of each gene and
chromosome pair
F. Genetics-Genetics--Branch
Branch of biology that deals with the
heredity and variation of organisms
G.Gamete
G.
Gamete---Mature
Mature germ cell, egg or sperm
1. Match terms associated with selecting and breeding livestock to the correct
definitions.
2. Select from a list hereditary characteristics that are determined by genes.
3 Describe
3.
D
ib how
h
heritability
h it bilit should
h ld affect
ff t selection
l ti off breeding
b
di stock.
t k
4. Match the types of livestock to the correct number of chromosome pairs.
5. Describe in a short paragraph how the genetic makeup of an animal is
determined.
6. Distinguish between dominant, recessive and incomplete dominant genes.
7. Distinguish between a simple gene inheritance and multiple gene inheritance.
8. Describe how the sex of the offspring is determined.
9. Distinguish between performance testing and progeny testing.
10. Match the different systems of breeding livestock to the correct definitions.
11. Estimate all p
possible gene
g
combinations when given
g
the matings
g using
g the
Punnett Squares procedure.
12. Observe mitosis and meiosis.
13. Study sex-linked traits.
14. Predict inheritance.
15. Study the influence of chance on inheritance.
16. Breed rabbits to study genetics.
I.
Terms and definitions
H. Fertilization--Union of the egg and sperm
I. Zygote--Fertilized egg
J. Homozygous--Animal that is pure for a certain gene such
as the polled gene
K. Heterozygous--Animal that is a carrier of a pair of unlike
genes
L. Phenotype--The outward appearance of the animal
M. Genotype--Genetic make-up of the animal
N. Lethal gene--Genetic factor that causes death of the young
during
g prenatal
p
life,, at birth or soon after
O. F1--Symbol which represents the first cross from a mating
P. F2--Symbol which represents second cross from a mating
Q. Heritability--Percentage of differences in a trait that can be
explained by inheritance as opposed to environment
R. Dwarfism--Inherited characteristic of cattle resulting in
small, deformed animals
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II.
Some hereditary characteristics
determined by genes
A.
B
B.
C.
D.
E.
F.
Body size
C l off hair
Color
h i coatt
Eye color
Length of leg
Dwarfism
Ability to fatten
IV. Chromosome pairs of
different species
A.
B
B.
C.
D.
E.
F.
Cattle--30 pairs
S i
Swine--19
19 pairs
i
Sheep--27 pairs
Chickens--39 pairs
Humans--23 pairs
Horses--32 pairs
III. Heritability
Some characteristics in animals are
highly heritable while others are not;
selection of breeding stock should be
weighted towards those factors which
have a high heritability
– See Hand-out
V. Genetic makeup
A. Determined by the union of two
cells one from each parent
cells,
B. Each cell contains one chromosome
from each pair in the parent or 1/2 the
total number of chromosomes
2
Cellular Division-Mitosis
Mitosis
• Interphase
– DNA duplicates
• Prophase
– Centrioles and spindles establish
– DNA condenses to form visible chromosomes (2 chromatids)
• Metaphase
– Chromosomes align in the middle of the cell
• Anaphase
– Spindles
S i dl attach
tt h and
d start
t t pulling
lli the
th chromosomes
h
apartt
– Chromatids separate
• Telophase
– Chromosomes are pulled to opposite ends of cell (poles)
• Cytokinesis
– Cell divides into two identical cells
Cellular Division-Meiosis
• Cycle happens twice
• Differences
– Prophase I
• Homologous chromosomes align
• Crossing over occurs (4 chromatids)
– Anaphase I
• Chromosomes divide
divide, not chromatids
• Second cycle is a reduction cycle but
similar to mitosis with no chromosome
pairs
3
Meiosis
Unique Features of Meiosis
VI. Genes
Shorthorn Incomplete
Dominance
A. Dominant--Genes that have the ability to cover up or
mask the presence of one member of a set of genes
i the
in
th F1 generation
ti
Examples: Pure polled; white face in Herefords;
drop ears in swine
(Note: Dominance is designated by a capital letter.)
B. Recessive--Genes that are covered up or masked in
the F1 generation
Example:
Horned; erect ears in swine
(Note: Recessive genes are designated by a small letter.)
C. Incomplete dominant--Genes that are neither
completely dominant nor recessive and which only
contribute to a certain characteristic
4
VII. Gene inheritance
A.
Simple--One pair of genes determines the
inheritance of a particular factor
B.
Multiple--Several pairs of genes
determine the inheritance of a particular
factor
Examples: Genes affecting meat production,
milk and butterfat production and growth
rate
(Note: Growth rate is hard to identify and is controlled by
several genes.)
VIII.
Sex determination
A.
A female egg contains an X chromosome
B
B.
A male sperm contains either an X or Y
chromosome
C.
Egg and sperm unite randomly to form
zygote
1.If egg and sperm contain like chromosomes (X
and X), a female is conceived
2.If egg and sperm contain unlike chromosomes (X
and Y), a male is conceived
5
IX. Production testing
Production testing is the practice of
evaluating and selecting animals on the
basis of progeny and performance
testing. This is done on characteristics
of economic importance.
A. Performance testing--Practice of
evaluating and selecting animals on the
basis of their individual merit or
performance
B. Progeny testing--Practice of selecting
animals on the basis of the merit of their
progeny (offspring)
X. Systems of breeding
A. Purebred--Member of a breed; animals which possess a
common ancestry and distinctive characteristics and are
either
ith registered
i t d or eligible
li ibl ffor registry
i t iin th
the h
herd
db
book
k
of that breed
B. Inbreeding--System of breeding in which closely related
animals are mated
Example: Brother x sister, sire x daughter, son x dam
C. Out-crossing--Mating of animals that are members of the
same breed but which show no relationship close up in
the pedigree
D. Grading up--System of breeding in which purebred sires
of a given pure breed are mated to native or grade
females
E. Crossbreeding--Mating animals of different breeds
XI. Punnett Squares system
showing gene combinations
A. Cross a pure, polled (PP) bull with
horned (pp) cows
1. Mating: PP x pp
2. F1 : Genotype--Pp
Phenotype--polled
B.
Cross F1 males (Pp) with F1 females (Pp)
1 Mating: Pp x Pp
1.
2.
F2
Genotypic ratio--1 PP:2Pp:1pp
Phenotypic ratio--3 polled: 1 horned
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2 Gene Crosses
♂
♀
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8