1. Phenotypic diversity Flashcards
Define DNA
double-stranded, helical nucleic acid molecule that is the carrier of genetic information and the fundamental substance of which genes are composed
Chromosome
a strand of DNA that is encoded with genes and made up of DNA tightly coiled many times around proteins called histones (for support)
Gene
Basic physical unit of heredity and the DNA sequence at specific location on a chromosome
allele
Alternative form of genes
>2 possible alleles at a locus
only two possible alleles one from sire and one from dam
Locus
a particular position or place where a piece of DNA is situated
Homozygote
individual carrying two alike alleles
Heterozygote
individual carrying two unlike alleles of a gene
Genotype
Genetic constitution of an individual
combination of alleles at a particular locus
Chromatid
each of the two thread-like strands into which a chromosome divides longitudinally during cell division
each contains a double helix of dna
Karyotype
the chromosome complement of an individual defined by the number, form and size of the chromosomes
how many chromosomes do cattle have (2n)
60
how many chromosomes do pigs have (2n)
38
Mendel’s first law
law of segregation
during gamete formation each member of the allelic pair separates from the other to form the genetic constitution
gamete only have half the number of chromosomes
thus each parent contributes only one allele to the offspring
Medel’s second law
law of independent assortment
genes assort independently during meiosis if all possible gametes are formed in equal proportions
pairs of alleles are passed on to offspring independently
offspring can possess combinations of genes that none of the parents had
Exceptions to Mendel’s law
Linkage
independent segregation depends on the genes being unlinked
loci are linked when located on the same chromosome
explain mendelian sampling
random samples of parental genes caused by segregation and independent assortment
give three external environmental factors
nutrition
parasites
climate
give three internal environmental factors
age of dam
birth status
gender
why bother with breeding and selection
in a given environment animals with superior genetics will always outperform animals with inferior genetics
so we can get better results with animals with good genetics if the selection and genetics complement the environment
Define selection
choosing and growing specific individual animals with desirable characteristics to breed with them and improve genetics of new generations
Define animal breeding
the directed development of breeds through the selection of parent animals expressing desired traits
list three types of selection and explain what is achieved through each
Directional-to move the mean of the population either higher or lower so that weaker genetics is eliminated
Stabilizing- to have a more centralized mean with less genetic variation away from the mean
Disruptive-eliminating the middle of a bell curve to disrupt the mean and move the variation further away from the mode
define traits
traits are observable/ measurable characteristics eg birthweight
define a Phenotype
the measured level of performance for a traits eg. 35 kgs.
