genetics genetics chapter 4 genetics is the science of heredity. heredity is the transmission of...
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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.