Genetics What is Genetics All body cells contain
Genetics
What is Genetics? All body cells contain “Blueprints” with instructions as to how an animal will look or act etc. One Gene comes from each parent (pairs) Genes are divided into sections (Chromosomes) that carry genes Sex chromosomes: male = XY, female = XX
Chromosome Chromosome- Rod like bodies that contain the genetic material of an individual. Chromosomes come in pairs and matching pairs are called homologous. Homologous chromosomes are similar in size and shape, and carry genes that affect the same traits.
DNA vs. RNA DNA- Deoxyribonucleic Acid- The Genetic material that makes up the chromosomes RNA- Group of molecules that are necessary for reading the DNA code and synthesizing proteins
Genes Genes- section on the chromosome that codes for a specific protein that determines how traits develop Locus- The location of genes on the chromosome. Plural is loci Alleles- Genes that occupy a specific locus but affect a trait in different ways. In humans, eye color is primary alleles are brown, blue, green. In cattle, black and red coat are alleles.
Mitosis Vs. Meiosis Mitosis: process of cell division that results in two genetically identical daughter cells developing from a single parent cell Meiosis: is the division of a germ cell involving two fissions of the nucleus and giving rise to four gametes, or sex cells, each possessing half the number of chromosomes of the original cell
How many chromosomes does each of the following have? Cattle 30 Swine 19 Sheep 27 Goats 30 Horses 39 Chickens 32 Humans 23 Turkeys 41
Types of genetic Traits Qualitative- Controlled by only one set of genes Coat color in angus cattle Polled or horned White color in swine White wool in sheep
Dominant Genes When one gene overshadows the other Angus Cattle: black is dominant over red Hereford: white face is dominant Hampshire Hog: white belt is dominant Horns are dominant Dominant= Capital Letter B
Recessive Genes When a gene will not be expressed when pair with a dominant gene Recessive genes can only express themselves if both genes are recessive Polled vs Horned (Pp) (pp) Black wool vs white (Ww) (ww) Red coat in angus Recessive= Lowercase Letter b
Genotype vs. Phenotypes Genotype- the genetic makeup of a trait Phenotype- The physical expression of a trait Two black genes or a black and red gene Black Two animals may have the same phenotype, but different genotypes
Homozygous vs. Heterozygous Homozygous- one that carries two genes for a trait Heterozygous- one that carries two different genes
Pedigree The record of descent of an animal, showing it to be purebred.
Punnet Square Determine the genetic probability of traits P = horned p = polled If a homozygous horned cow (PP) is mated to a homozygous polled bull (pp), what percent of the calves will be horned, polled?
Punnet Square
Punnet Square If a homozygous horned cow (PP) is mated to a heterozygous horned bull (Pp), what percent of the calves will be polled?
Punnet Square
Sex Linked Genes Some recessive genes are attached to the X and Y chromosomes Humans: Colorblindness and Baldness are on the X chromosomes In Men, traits expressed anytime present In Women, must have two recessives to show trait Children get baldness from mothers
Punnet Square: What sex will the offspring be?
If Dad is bald, will you be bald?
Baldness is carried by the mother
What is Mom is bald?
Incomplete Dominance If both genes express themselves Shorthorn Cattle: Red male mated to a White female = Roan calf RR + WW = RW
Punnet Square Shorthorn Cattle R = Red W = white RW = roan If a red bull (RR) is mated to a white cow (WW), what color will the calves be?
Shorthorn: Red X White
Punnet Square If a red bull (RR) is mated to a roan (RW) cow, what color will the calves be?
Shorthorn: Red X Roan
What if Both Parents are Roan?
Undesirable Characteristics Dwarfism Monorchid = only one testicle descends Cryptorchid = no testicles descend Short ears & tails
Mutation Dramatically different from what is expected genetically Horned calf from polled parents Loss of some or extra body parts Lethal Mutation: causes death at birth Sublethal Mutation: limits animals ability to grow to maturity Beneficial Mutation: loss of tail in lambs
Abnormality Similar to a Mutation, only it is caused by something in the environment Siamese twins
Heritability Chance that traits will be inherited Low: multiple births, fat covering Medium: birth wt, wean wt, milk, wool grade, carcass wt, rate of gain High: Loin eye area, fleece length & quality
Heritability Currently have ewes that wean 70 lb lambs Want to raise weaning wt to 110 lbs Select a ram with a wean wt of 110 lbs Heritability of weaning wt is 30% What can you expect new lamb crop to weigh at weaning?
Heritability What is the difference in current weaning wt and that of the new ram? 110 - 70 = 40 lbs Heritability % x difference 30% x 40 = 12 lbs Can expect a gain in weaning wt of 12 lbs 70 lbs + 12 lbs = 82 lbs
Purpose in Livestock Improving by selecting quality sires and dams
- Slides: 40