Genetics Lecture

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Genetics Lecture

• Dr. Mickey A. Latour
• Purdue University

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Genetic Principals

• The father of genetics Gregor Mendel
  (1822-1884).

• Simple genetic crosses using pea plants.

• DNA was discovered in the mid - 1900s.

• Today much of the genetic gains have been
  through
• the use of molecular biology.

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Genetic Terms

• Genes
• Diploid
• Haploid
• Homozygous
• Heterozygous
• Dominance
• Recessive
• Intermediate Dominance
• Monohybrid
• Gamete
• Genotype
• Phenotype

are located on chromosomes in nuclei of cells.
means chromosomes exist as pairs.
means a single copy of the genetic material.
are identical gene pairs.
are unlike gene pairs.
mask the expression of all other genes.
expression is masked by other genes.
Intermediate to both parents
single gene cross
the ova or sperm (haploid)
gene makeup
appearance of the animal
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Gene Pairings

• Genes pair up in certain locations to code for
  growth, fat, hair color, horn type, etc.
  Pairings are made at molecule level.

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Dominant and Recessive Genes
Horned (pp)
Polled (PP)
Polled (Pp)
F1 Generation
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Co-dominant Genes
White (rr)
Red (RR)
Roan (Rr)
F1 Generation
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Crossing Two Gene Pairs
White, Horned (rrpp)
Red, Polled (RRPP)
Roan Polled (RrPp)
F1 Generation
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What if?

• What if you crossed a roan polled bull with a
  roan horned cow? Keep in mind, the bulls mother
  had horns.

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Genes

• Epistasis is a gene or genes of one pair which
  masks the effect of the gene of another pair.

Example Coat color in Labrador Retrievers ee is
epistatic to B, b EEBB EEBb EeBB EeBb EEbb Eebb ee
BB eeBb eebb
eepure yellow BBpure black EEbbpure chocolate
Black
EE no yellow gene Ee yellow carrier but
appears either black or chocolate ee yellow Lab
Chocolate
Yellow
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Genes

• Accomplish their function through
• - Replication
• -Transcription
• -Translation

Replication is a process which produces units
like themselves.
Transcription is a process which the information
is transformed to an appropriate place for
translation.
Translation is a process by which molecules
(proteins) are formed.
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Cell Structure
Nucleus
Golgi
Ribosome
Endoplasmic Recticulum
Lyosome
Vacuole
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DNA and RNA
DNA deoxyribonucleic acid RNA ribonucleic acid
DNA
- double strand - helix structure - organic
base(s) adenine, guanine, thymine, cytosine -
discovered by Watson and Crick, 1953
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DNA and RNA
DNA deoxyribonucleic acid RNA ribonucleic acid
RNA
- usually single strand - adenine, guanine,
uracil not thymine, cytosine
Three general types -messenger RNA mRNA initial
message from DNA -transfer RNA tRNA recognizes
the mRNA codons -ribosomal RNA rRNA assembly
area for translation
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Breeding Methods

• Inbreeding

• Out Breeding

• Random Mating

• Cross Breeding

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Choosing a Mating System

• Gene Purity homozygous genes may be wanted

(Inbreeding)

• Conversely, you may need to choose a mating
  system,
• which fosters some hybrid vigor in the
  offspring
• (Out breeding)

• Some producers are not concerned with mating
  orders
• and allow their animals to mate randomly
  (Random
• Breeding)

• Crossing of animals from two different pure
  stocks to
• produce a terminal F1 cross for production
  purposes and
• maximum hybrid vigor.

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Inbreeding

• Production of offspring by parents more closely
  related than the average of the breed

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Inbreeding - Genetic Effect

• Fosters gene purity via increasing homozygous
  gene pairs

• Increases uniformity within the herd to a
  certain point!

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Inbreeding - Genetic Effect

• Uncovers recessive genes
• Increases incidence of genetic defects

• Aids in eliminating undesirable traits

• Decreases performance in traits related to
  physical
• fitness (i.e., survival to weaning).

• Lowers fertility if intensely performed.

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Inbreeding - When to Use

• Use for superior animals
• To develop a specific line of animals

• Trying to uncover specific genes (good or bad)

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Out Breeding (Crossing)

• Defined mating of individuals less closely
  related than the average of the breed

• Involves relatively unrelated animals of the
  same
• breed

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Out Breeding (Crossing) Genetic Effect

• Decrease the proportion of homozygous gene pairs.

• Increase the amount of heterozygous gene
  pairs.

• Decrease gene purity

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Out Breeding (Crossing) Phenotypic Effect

• Improves traits related to physical fitness

• Can provide the most heterosis within a breed

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Out Breeding (Crossing) When to Use

• In building a herd.

• When an undesirable trait appears

• Move from out breeding towards inbreeding as
• the genetics/herd improves.

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Random Breeding

• Defined mating without regard to relationship
  includes random assignments of females to more
  than one male (e.g., pasture type breeding)

• Largely used on commercial herds

• Cant prove identity to breed association

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Crossbreeding

• Defined mating two different animals from pure
  stock

• Increases the amount of heterozygous gene pairs
  
• (F1 F2 Generation)

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Crossbreeding - Why do it?

• To obtain the best traits from each breed

• Introduce new genetic material when selection
• differential has become small

• To obtain hybrid vigor

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Hybrid Vigor Example

• Breed A had a weaning weight of 520 lb.
• Breed B had a weaning weight of 600 lb.
• The herd average is 560 lb.
• So, what is the hybrid vigor in your current
  herd given the A by B cross and new offspring
  weight of 590 lb?

590 - 560 30 pounds net difference in weight
30/560 100 5.4 increase due to hybrid vigor
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Affected traits

• Most important traits are affected by several
  to many gene pairs.

• Geneticists utilize population genetics (large
  number of
• observations) to determine heritability of
  traits.

• To do so, they study data from studies where
  the environment
• effects are kept to a minimum (controlled).

• These effects are determined in order to know
  those effects
• due to heredity.

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Rules for Genetic Improvement

• 1. Have maximum genetic variation
• 2. Select for important traits with moderate to
  
  high heritability estimates.

3. Make accurate measurements of traits in
selection program.
4. Use selected animals effectively