Download animal science genetics

Genetics and Heredity in
Agriculture
Biology Agriculture
Genetics and Cells?
How do Genetics and Cells Relate?
 Cells play a main role in genetics

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Cells contain all the genetic information in
the nucleus called DNA
How those cells divide play a huge role in
how traits are passed on to offspring.
Cell Growth

All cells come in different sizes and shapes.
Diffusion in fast and effective over short
distances.

It become slow and inefficient over long
distances.
If a cell and a mitochondria 20cm in diameter – it
would take months before it would receive molecules
that entered the cell membrane.

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Cell Growth

Surface area-to-volume ratio
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Area: the surface included in a set of lines.
Volume: space occupied as measured in cubic
inches.
Ratio: the relationship in quantity, amount, or size
between two or more things.
Cell Reproduction

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Cell division in necessary to form multicellular organisms.
Asexual Reproduction:
–

Production of offspring from one parent cell.
Sexual Reproduction:
–
Formation of offspring from the union of two
gamete cells .
Asexual Reproduction

Type of reproduction where one parent
cells divides and produces two identical
cells.
–
Advantage:
 Only
one parent cell is needed
 More offspring is created at a faster rate then
meiosis.
–
Disadvantage:
 No
genetic diversity, except with mutations.
Sexual Reproduction

Results from the joining of two highly
specialized cells.
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
Sperm Cells
Ovum Cells or Egg Cell
Fertilization:
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Sperm cell and ovum combine to form a Zygote.
Sexual Reproduction

Pattern of reproduction that involves the
fusing of a sperm cell and an ovum cell.
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Advantage:

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Sexual reproduction can help to introduce genetic
variation into a specie which can be beneficial in the
long run
Gives some species a better opportunity to adapt to new
environments.
Sexual Reproduction
–
Disadvantage:
 Two
organisms are needed to reproduce
 “Survival of the fittest” Those organisms that
have the best adaptations to the environment
survive and that is how those adaptations
occur, due to the genetic diversity.
Genetics

Genotype:
–
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Phenotype:
–

The genetic composition of an individual
How the alleles express themselves.
Ex. Two black calves might have the same
phenotype, but different genotypes.
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One may be Heterozygous, (Bb)
One may be Homozygous, (BB)
Genetics

Homozygous:
–
–

Genes that possess two dominant alleles or two
recessive.
TT or tt
Heterozygous:
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Genes that possess one dominant and one
recessive trait.
Tt
Probability in Genetics


Probability: the likelihood that a particular
event is going to happen.
Two Pennies
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Heads = A - for attached earlobes
Tails = a - for free hanging earlobes
Flip them 20 times and record your genotype.
The Punnet Square


Mendel's pea plants
Tall = TT
P1 Generation

T
T
t
Tt
Tt
t
Tt
Tt
Short = tt
F1 Generation
The Punnet Square


Mendel's pea plants
Tall = Tt
F1 Generation

T
t
T
TT
Tt
t
Tt
tt
Tall = Tt
F2 Generation
Gender

The sex of an animal is determined by
the sex chromosomes.
–
There are two types,

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X shaped chromosomes
Y shaped chromosomes
Vertebrate males have a XY
Vertebrate females have a XX
Sex-linked Genes

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Fruit Flies inherit sex chromosomes the
same a humans.
Traits located on the sex chromosomes are
called sex-linked traits.
All sex-linked traits are located on the X
chromosomes.
Sex-linked Genes
Male Fruit Flies
Phenotype = White Eyes
Genotype = Xr Y
Female Fruit Flies
Phenotype = White Eyes
Genotype = Xr Xr
Sex-linked Genes
Xr
Y
XR
XRXr
XRY
XR
XRXr
XRY
Sex-linked Genes
XR
Y
XR
XRXR
XRY
Xr
XRXr
XrY
Incomplete Dominance

When traits are inherited incompletely, or
they mix.
Red Carnations
Genotype (RR)
White Carnations
Genotype (R’R’)
Incomplete Dominance


When they
reproduce the
offspring are pink
in color.
New phenotype
occurs because
the trait that
controls pigment is
affected.
Incomplete Dominance
R’
R’
R
R’R
R’R
R’R
R’R
R
Incomplete Dominance
R’
R
R’
R’R’
R’R
R’R
RR
R
Codominance

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The expression of both
alleles
Neither one of the alleles
are dominant or
recessive, and is
expressed in the offspring.
Ex. - In some chickens, alleles
for feather color are
codominant.
Codominance

Alleles are written with superscripts.
Genotype = FB FB
Phenotype = Black
Genotype = Fw Fw
Phenotype = White
Codominance
FB
FB
Fw
FBFW
FBFW
FBFW
FBFW
Fw
Codominance

Other example of Codominance.
–
Shorthorn Cattle
Environmental Influences

The genetic make-up of an organism only
determines the potential of an organism.
Environmental Influences

External Influences
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Temperature
Light
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Nutrition
–
Environmental Influences

Internal Influences
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Internal body functions

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Hormones
Age