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Genetics
Genetics
Genetics is the study of inheritance, how certain traits are passed from one
Generation to the next. Early people did not understand that genetics as well
As environment shape each individual.
Gregory Mendel is considered the “Father” of genetics. He was born in Germany
1n 1822. He studied philosophy and physics and entered a religious order in 1843.
He continued his education through the church. He was an avid gardener and the
Variation in pea plants peaked his educated mind. He studied how the plants
Passed traits like plant size and pea texture to the next generation. His math and
Physics helped him plan experiments to determine what was going on. He died in
1884 and his findings were mostly forgotten. In the early 1900’s interest in producing
Better agricultural product caused his experiments to be rediscovered.
Basic genetics is often called Mendelian Inheritance.
Animal cell part review
1. Cell membrane: limits the cytoplasm with
In the cell.
2. Pinocytic vesicle: small bleb or opening
To the outside on the cell wall
3. Cytoplasm: transparent, semi-fluid subStance in which other organelles float.
4. Endoplasmic reticulum: membrane used
For transportation, metabolizing lipid, lined
With RNA
5. Golgi bodies: stacks of saucer shaped
Disks, involved in synthesis of carbohydrates
6. Centrosome : near nucleus involved with
Formation of spindle during cell division.
7. Lysosomes: spherical bodies which contain digestive enzymes.
8. Mitochondria: The center for respiratory metabolism in the cell
9. Vacuole: Small spheres which are concerned with storage and excretion.
10. Nucleus: central body of the cell contains a nuclear sap (karyolymph)
11. Nucleus: a dense body contains RNA This nucleus disappears during cell division.
12. Nuclear membrane: semi-permeable membrane that separates nucleus from cytoplasm.
Nucleus:
Made up of pairs of genetic material called
Chromosomes. The chromosomes come in pairs.
Each species has a certain number of pairs of
Chromosomes.
Man 23 Pair or 46 chromosomes
Swine 40 pair or 80 chromosomes
Cattle 30 pair or 60 chromosomes
Sheep 32 pair or 64 chromosomes
Horse 30 pair or 60 chromosomes
Each chromosome is made of genes. The combinations of genes is what express
Itself in the individual.
The genes are made up of individual DNA. When the nucleus replicates it copies
The DNA. Sometimes the replication process makes mistakes. That is how
Mutations happen.
Cell division:
Mitosis: Normal cell division where two new
Cells are created with the same number of
Chromosomes.
Pro Phase: two centrosomes appear and
Start to form spindles which the
Chromosomes will align themselves with
Their sister cells.
Metaphase: The chromosomes align
Themselves on the spindles between
The centrosomes.
Anaphase: proteins that connect sister
Cells dissolve and the spindle fibers
Shorten pulling chromosomes to
Opposite ends of the cell.
Telephase: the cell membrane “pinches”
Off between the two ends of the cell that
The chromosomes have segregated to.
Cytokinesis: the completion of the
Splitting of the cell
Meiosis:
Cell division in which the resulting cells have only
Half of the genetic information (chromosomes)
That the original cell had. Used for gamete or
Sex cell production (egg and sperm cells)
Fist a type of mitotic multiplication of chromosomes
Occur, but some information is mixed between the
Two sister chromatids.
The cell divides with sister Chromatids separated
forming two daughter cells.
A second division takes the two daughter cells and
Splits them forming 4 cells with half of the chromosomes
From each sister chromatids.
Fertilization:
The union of an egg cell and sperm cell forms
A zygote.
The resulting cell has a complete set of chromosomes
One half from the paternal (father) side and one
Half from the maternal (mother) side.
The zygote continues to grow geometrically 2 cells, 4 cells, 8 cells, 16 cells etc.
As the cells grow it reaches a point where it is called a blastula, early in the blastula
stage it can be separated (embryo splitting ). It fold inward on itself and forms
what will become the gastro-intestinal tract (digestive).
At an early stage animal zygotes form the umbilical cord and attach to the
Uterine wall. The umbilical cord blood vessels pass very close
the blood vessels of the uteri an wall and food and waste is
passed through a semi-permeable membrane to support
the fetus.
Formation of twins
If the blastula separates on its own it forms 2 individual blastulas with the
Same genetic information. The type of twins arising from a single egg
Are called Identical twins. These twins will be the same sex and be extremely
Similar in their traits (color patterns, etc.). Embryo splitting tries to
imitate this type of twin.
If more than one egg is shed off the ovary at ovulation each egg
Can be fertilized independently of the other. The type of twins produce
By this process are called fraternal twins. They do not have to be the
Same sex, or have very many genetic traits in common.
Producers are now selecting superior females and through the use of
Drugs causing them to super-ovulate, produce many eggs at ovulation.
They may then AI the individual or fertilize the eggs in vitro (outside the body).
The fertilized eggs can then be transplanted in donor individuals at the same
Stage of gestation and the donor will raise the young. This process is called
Embryo transfer
Traits
The traits an individual has and the traits we see they have are two different
Things.
Genotype: is the actual genetic make up of the individual. It is the
Combination of genes that formed the individual from fertilization.
Think of it as the potential that the individual has according to genetics.
Phenotype: is what we physically see. Phenotype is influenced by
Environment. If an individual has a genotype to gain 3 pound a day
And you don’t feed them enough food it will not produce 3 pounds a
Day gain. The environment limited the individuals performance.
Classification of traits
The most expressive traits or genes are called dominate genes and are
Denoted by a capital letter. Being polled in the beef species is dominate.
Less expressive traits or genes are called recessive genes and are denoted
By a small letter. A red hair coat in most beef breeds is recessive to dark
Or black hair coats.
Homozygote individuals have either both dominate or recessive genes for a
Particular trait (BB, bb) while heterozygotes have one of each (Bb)
Chi square crosses:
A Chi square is a simple method to determine the expected outcomes
Of crossing animals with different traits.
The F1 (family 1) is the cross between two individuals that have a known
Trait make up. If only one individual appears to be dominate and you
Cross them with an individual that is recessive for the same trait you
Should be able to determine if the dominate appearing animal is homo, or
Heterozygote for the trait. How?
The F2 (family 2) is a cross between animals of the F1 generation. Using
Our knowledge of trait expression we would expect to see a certain ratio
Of offspring if the F2 individuals were homozygotes or heterozygotes.
By working the square we can predict or compare what really happened
To what to what we predicted to determine the genetic makeup of
Individuals.
Simple crosses using a square are those that compare one or two
Traits. Predicting multiple trait outcomes requires the use of
Probability.
Other trait combinations.
Incomplete Dominance:
Where the dominant gene cannot completely overcome the less
Expressive gene. If the dominate gene for hair coat is Red R and
The recessive hair coat is White r and individual with a genotype
Of Rr appears a roan color.
Sex linked:
Some traits are expressed only in the males or females of a
Species. These traits are connected to a gene on the sex
Determining chromosome.
Lethal genes:
These genes are lethal in the homozygous state. They usually cause
Death before the zygote is born. Abortions may happen for no
Apparent reason.
Sex determination:
In the mammal world males have the sex genes XY, while females are XX.
This is true in 95-99% or males and females…..there are exceptions.
If this is true then during meiosis the sex cells developed by the male are
Either X or Y, and the sex cells of females will produce cells that only
Have an X. The egg produced by the female has only the X to offer in
The sex determination department. It depends on the sperm cell that
Fertilizes the egg what sex it will develop into. If a sperm cell with an
X fertilizes the egg a female zygote will result. If a sperm cell with a
Y fertilizes the egg a male zygote will result. The sex cells of the male
Determines the sex of the zygote.