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Genetics Modified by Georgia Agricultural Education Curriculum Office July 2002 August 2008 Genetics • Is the science of heredity. • Heredity is the transmission of genetic or physical traits from parent to offspring. August 2008 Gregor Mendel • Austrian Monk • Considered the “Father of Heredity” • He conducted plant breeding experiments in their monastery garden. • In 1865 he made his work public, units of inheritance. August 2008 What makes us unique? • Each of the 100 Trillion cells in our body except the red blood cells contains the entire human genome, in the nucleus of every cell is the genetic information “blueprint” to construct the individual. • It is the Deoxyribonucleic acid (DNA) • Function of DNA – Genetic code for almost every organism. – Provide template for protein synthesis. August 2008 Composition of DNA • The structure of DNA was discovered by Watson and Crick in 1953. • It is a twisted double helix molecule, containing sugar, phosphates, and nitrogenous bases. • The sugar is deoxyribose and the phosphoric acid molecules are always the same and provides for the structure (side of the ladder). • The only difference between us is the order and arrangement of the four bases (rungs of the ladder). August 2008 Bases of DNA • • • • • • Adenine= A Thymine= T Guanine= G Cytosine= C A always pairs with T C always pairs with G August 2008 Bases of RNA • • • • • • • Adenine= A Uracil= U Guanine= G Cytosine= C G always pairs with C T from the DNA = A in the RNA A from the DNA = U in the RNA August 2008 DNA Model August 2008 Chromosomes • The DNA in every cell is located in rod like segments called chromosomes • Chromosomes occurs in pairs in every cell of our body except in the sperm and ovum. • Chromosomes numbers are the same for each species. August 2008 Chromosome Numbers Species Cattle Swine Sheep Horse Human Chicken Goat Donkey August 2008 Diploid # 60 38 54 64 46 78 60 62 Haploid # 30 19 27 32 23 39 30 31 Chromosomes • There are 2 sex chromosomes included in the diploid number of the chromosomes. • All of the other chromosomes are referred to as autosomes. • In mammals if the sex chromosomes are alike, XX it results in a female. • If the sex chromosomes are different, XY it results in a male. August 2008 Sex Determination • Females contribute an X chromosome towards the sex of their offspring. • Males can contribute an X or a Y chromosome toward the sex of their offspring. • Absence of an Y chromosome results in a the embryo developing into a female. • Presence of an Y chromosome results in the embryo developing into a male. August 2008 Sex Determination • Gametogenesis = Formation of gametes through meiosis. • Male = 4 viable spermatids • Female = 1 viable ovum, 3 polar bodies. August 2008 Tell me what I am ????? August 2008 Tell me what I am ????? August 2008 Cell Division • Meiosis – Is the form of cell division which results reducing the chromosome number from the diploid # to the haploid #. – Occurs only in the sex cells, sperm and ovum. • Mitosis – Is the form of cell division which results in the formation of identical daughter cells, keeps the chromosome number constant. – Tissue growth and repair. – Occurs throughout the body except in the sex cells. August 2008 Genotype or Gamete • Genotype contains two copies of the gene. – AaBB • Gamete (sex cells) contains only one copy of the gene. – AB • Determine the possible gametes of AaBB – AB August 2008 aB Gamete or Genotype • • • • • • • State if its a gamete or genotype. Aa D DdEeFFgg sRtxyq AaBBeeFF adgEFT August 2008 List all the possible gametes. • • • • • From the genotype AaBb AB Ab aB ab August 2008 Genes • Chromosomes contains several units of inheritance “genes”. • Genes usually occurs in pairs, one from each parent. • Some traits are inherited directly from one set of genes. • Some traits are inherited through several sets of genes. August 2008 Genes • It was presumed that we were composed of about 100,000 genes to construct us. • Today, research has proven that number is a lot less than 100,000. • Extra credit for the student that can find an article about the current number of genes. August 2008 Terms to know • Homozygous- contains 2 identical genes for the same trait, AA, BB, cc • Heterozygous- contains 2 different genes for the same trait, Aa, bB, Cc • Phenotype- Outward appearance of a trait, coat color, polled, horned. • Genotype- Genetic classification of a gene, AA, Aa, aa. • Allele- Location of a gene on the chromosome. • F-one = First cross mating. • F-two = Second cross mating. August 2008 What are dominant genes? • The gene that express itself, the powerful and dominant gene. • It has the power to overshadow the recessive gene when there is complete dominance. • Some examples are: – White faced in cattle – Droopy ears in swine – Polled in cattle – Black coat color in Angus cattle August 2008 What are Recessive Genes? • The gene that is overshadowed by a dominant gene • Recessive genes can only express themselves in the absence of the dominant gene • Polled vs Horned (Pp) (pp) • Black wool vs white (Ww) (ww) • Dwarfism vs normal size (dd) • Albino August 2008 Punnet Square • • • • • Angus- Black coat color is dominant. BB = Homozygous Dominant and Black Bb = Heterozygous and is black bb = Homozygous recessive and red A heterozygous bull is mated to 50 homozygous recessive cows. • How many calves are black? • How many calves are red? • What is the genotypic and phenotypic ratios? August 2008 Punnet Square August 2008 B b b Bb bb b Bb bb Results • 2 heterozygous = Bb • 2 Homozygous Recessive bb • 25 Black, 25 Red • Genotypic ratio = 0:2:2 • Phenotypic ratio = 2 Black: 2 Red August 2008 What are 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 August 2008 If Dad is bald, will you be bald? Y X B X X August 2008 X X B X X B X Y X Y Baldness is carried by the mother X X B X August 2008 X X B X X Y X BY X Y What if Mom is bald? X X B X B August 2008 X X B X X B Y X BY XB Y What is Incomplete Dominance? • If both genes express themselves • Shorthorn Cattle: Red male mated to a White female = Roan calf • RR crossed rr = Rr August 2008 Punnet Square • • • • • Shorthorn Cattle RR = Red rr = white Rr = roan If a red bull (RR) is mated to a white cow (rr), what color will the calves be? August 2008 Shorthorn: Red X White R August 2008 R r Rr Rr r Rr Rr Punnet Square • If a red bull (RR) is mated to a roan (Rr) cow, what color will the calves be? August 2008 Shorthorn: Red X Roan August 2008 R R R RR RR r Rr Rr What if Both Parents are Roan? August 2008 R r R RR Rr r Rr rr What is a 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 August 2008 What is Heritability? • Chance that traits will be inherited • Low: multiple births, fat covering • Medium: birth wt, wean wt, milk, wool grade, carcass weight, rate of gain • High: Loin eye area, fleece length & quality August 2008 Mating Systems • Upgrading: mating purebreds with grade animals • Inbreeding: mating closely related animals • Linebreeding: mating distantly related animals • Outcrossing: mating unrelated animals in the same breed. • Crossbreeding: mating animals of same species but different breeds. August 2008 What is Hybrid Vigor? Heterosis • Offspring will outperform either of the parents • Corn Breed A yields 100 bu/acre • Corn Breed B yields 100 bu/acre • Crossbreed A & B yields corn that yields 200 bu/acre • Vigor only expressed in crossbreeding August 2008 The End August 2008