GeneticsGenetics

Chapter 4

GeneticsGenetics

• Is the science of heredity.• Heredity is the transmission of

genetic or physical traits from parent to offspring.

Gregor MendelGregor 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?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 DNAComposition 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 DNABases of DNA

• Adenine= A• Thymine= T• Guanine= G• Cytosine= C• A always pairs with T• C always pairs with G

Bases of RNABases 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 ModelDNA Model

ChromosomesChromosomes

• 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 NumbersChromosome Numbers

Specie Diploid # Haploid #Cattle 60 30Swine 38 19Sheep 54 27Horse 64 32Human 46 23Chicken 78 39Goat 60 30Donkey 62 31

ChromosomesChromosomes• 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 DeterminationSex 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 DeterminationSex 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 ?????

Tell me what I am ?????Tell me what I am ?????

Cell DivisionCell 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.

Genotype or GameteGenotype 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 GenotypeGamete or Genotype

• State if its a gamete or genotype.

• Aa• D• DdEeFFgg• sRtxyq• AaBBeeFF• adgEFT

List all the possible List all the possible gametes.gametes.

• From the genotype AaBb• AB• Ab• aB• ab

GenesGenes

• 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.

GenesGenes

• 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 knowTerms 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?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 What are Recessive Recessive GenesGenes??

• 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 SquarePunnet 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 SquarePunnet Square

B b

b

b

Bb bb

Bb bb

ResultsResults

• 2 heterozygous = Bb

• 2 Homozygous Recessive bb

• 25 Black, 25 Red• Genotypic ratio

= 0:2:2• Phenotypic ratio

= 2 Black: 2 Red

What are What are Sex Linked Sex Linked GenesGenes??

• 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 If Dad is bald, will you be bald?bald?

X Y

X XX X Y

XX XYX

B

B

B

Baldness is carried by the Baldness is carried by the mothermother

X Y

X XX X Y

XX XYX

BB B

What if Mom is bald?What if Mom is bald?

X Y

X XX X Y

XX XYX

BB B

B B B

What is What is Incomplete Incomplete DominanceDominance??

• If both genes express themselves

• Shorthorn Cattle: Red male mated to a White female = Roan calf

• RR crossed rr = Rr

Punnet SquarePunnet 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 WhiteShorthorn: Red X WhiteR R

r

r

Rr Rr

Rr Rr

Punnet SquarePunnet Square

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

Shorthorn: Red X RoanShorthorn: Red X RoanR R

R

r

RR RR

Rr Rr

What if Both Parents are What if Both Parents are Roan?Roan?R r

R

r

RR Rr

Rr rr

What is a What is a MutationMutation??• 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?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 SystemsMating 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 What is Hybrid VigorHybrid Vigor? ? HeterosisHeterosis

• 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 EndThe End

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