Genetics Chapter 4

Genetics Is the science of heredity. Heredity is the transmission of genetic or physical traits from parent to offspring.

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.

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.

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).

Bases of DNA Adenine= A Thymine= T Guanine= G Cytosine= C A always pairs with T C always pairs with G

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

DNA Model

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 specie.

Chromosome Numbers Specie Diploid # Haploid # Cattle 60 30 Swine 38 19 Sheep 54 27 Horse 64 32 Human 46 23 Chicken 78 39 Goat 60 30 Donkey 62 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.

Sex Determination Female can contribute only a X chromosome towards the sex of their offspring. Male 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.

Sex Determination Gametogenesis = Formation of gametes through meiosis. Male = 4 viable spermatids Female = 1 viable ovum, 3 polar bodies.

Tell me what I am ?????

Tell me what I am ?????

Cell Division Meiosis Mitosis 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.

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 aB

Gamete or Genotype State if its a gamete or genotype. Aa D DdEeFFgg sRtxyq AaBBeeFF adgEFT

List all the possible gametes. From the genotype AaBb AB Ab aB ab

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.

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.

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.

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

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

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?

Punnet Square

Results 2 heterozygous = Bb 2 Homozygous Recessive bb 25 Black, 25 Red Genotypic ratio = 0:2:2 Phenotypic ratio = 2 Black: 2 Red

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

If Dad is bald, will you be bald?

Baldness is carried by the mother

What if Mom is bald?

What is Incomplete Dominance? If both genes express themselves Shorthorn Cattle: Red male mated to a White female = Roan calf RR crossed rr = Rr

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?

Shorthorn: Red X White

Punnet Square If a red bull (RR) is mated to a roan (Rr) cow, what color will the calves be?

Shorthorn: Red X Roan

What if Both Parents are Roan?

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

What is 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

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.

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

The End You can use your notes to do the next two worksheets.