Genetics Flashcards
Define genetics
Study of heredity
When and who started modern genetics? (Quantitative genetic testing)
Gregor Mendel 1800s
Define phenotype
Physical appearance of animal
Physical expression of genes
Define genotype
Genetic makeup
Define genome
Entire genetic material of an animal
Define genes
Functional units of inheritance
Polymer of DNA and its 3 parts
Nucleotide
1. 5 carbon sugar (ribose vs. deoxyribose)
2. Phosphate
3. Nitrogenous base
5 main nitrogenous bases
Pyrimidines: cytosine and thymine (uracil)
Purines: Adenine and Guanine
Significance of base pairing
Easy to exactly replicate (duplicate) accurately
Define mutation
When replication is not exact due to chemical change in DNA
(This word is overused)
Define migration
Bringing new genotypes through breeding stock into a population
Define selection
Using some animals more than others as parents
Natural: by nature
Artificial: by management
What are the products of genes?
Protein molecules via synthesis of amino acids
Triplet codes vs. codon
Triplet code: DNA
Codon: RNA
- 64 possibilities for 20-21 amino acids
Define autosomes
Chromosomes in somatic cells
How many chromosome pairs do humans, horses, cattle, wheat, and fruit flies have?
Humans- 23
Horses- 32
Cattle- 30
Wheat- 21
Fruit fly- 4
Define transcription
Synthesis of mRNA strand by “copying” a DNA segment
Define translation
Production of amino acids from RNA codon sequences
Protein synthesis pathway
DNA (transcription in nucleus) mRNA (translation in ribosomes) proteins folding
3 types of RNA
Messenger (mRNA)- contains information to directs protein synthesis
Ribosomal (rRNA)- structure and function of ribosomes
Transfer (tRNA)- identifies codons in mRNA and brings correct amino acid
Define locus
Location of a particular gene on a chromosome (address)
Define homologous chromosomes
Same loci and structure
Define alleles
Different forms of the same gene
Define homozygous
Genes are alike for a particular trait (same alleles)
Define heterozygous
Genes are not alike for a particular trait (different alleles)
Define dominant
An allele that overpowers and prevents the expression of another allele
Define recessive
An allele that is expressed only when animal is homozygous for non-dominant allele
Where does random (independent) assortment occur?
Meiosis
3 gene actions
Qualitative inheritance (simple traits)
Sex-linked inheritance
Quantitative inheritance (polygenic traits)
Describe qualitative inheritance
Controlled by a single gene
Phenotype is discontinuous
(Ex. Cow coat color)
Define codominance
When two alleles are both expressed in heterozygote
Ex. Checkered chickens
Define incomplete dominance
Get 3 distinct phenotypes instead of 2
Hetero is dilute or medium
(Ex. Pink flower)
Sex-linked inheritance in mammals vs. birds/ reptiles
Mammal
F- XX
M- XY
Reptiles/ Birds
F- ZW
M- ZZ
Genes uncontested on sex chromosome is expressed no matter what.
Describe quantitative inheritance
Many genes involved (additive effects)
Phenotypes described by measurements
Continuous distribution of phenotypes
Define heterosis
Other names: overdominance + hybrid vigor
Heterozygote shows better results than either homozygote
Often in crossbreeding
Most common equation in genetics
Phenotype= genotype + environment
(Means we must standardize environment for studies)
Formula for genetic progress
Genetic gain/year= (heritability x selection differential (intensity))/generation interval in years
What is heritability?
(h^2)
Percent of trait dictated by genetics
Estimates variation in phenotypes
Ranges from 0-1
.4-.5 for weight
.1 for health, fitness, reproduction
How to calculate selection differential?
Compare average of selected male/female with population average and divide by two.
Then Add to pop. Avg.
What is the generation interval?
The average age of parents when offspring born.
Evidence of genetic change
Meat to bone ratio in turkey
Lean pigs
3 selection methods
Tandem- one trait at a time
Independent culling levels- minimal acceptable levels assigned to traits
Selection index- traits evaluated and expressed as a single score (can include economics and correlation)
Define registered
Recorded in some breed association and meets criteria outlined by org.
Define “grade”
Not registers
Could be about same genetically as registered
3 effects of inbreeding
Increases homozygosity
Decrease reproductive performance and growth
More susceptible to stress and disease
Define line breeding
Milder form of inbreeding
Emphasizes one outstanding ancestor
3 types of outbreeding
Species cross: ex. Mule or beefalo
Crossbreeding: same species by different breed (max. Heterosis and breed complementation)
Outcrossing: mating unrelated animals within a breed
How fast can inbreeding effects be eliminated?
In one generation
Positive vs. negative correlations
Positive= both increase together
Negative= one goes up and the other decreases
Close to 1 or -1 is stronger
