Genetics study of heredity Gene determinant of heredity Chapter is outline of basic principles of genetics wwwsardisagovau livestock meatwoolbreeding genetics Cell Theory of Inheritance ID: 911608
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Slide1
Fundamental Principles of Genetics (Chapter 8)
Genetics – study of heredityGene – determinant of heredityChapter is outline of basic principles of genetics
www.sardi.sa.gov.au/
livestock
/meat_wool/breeding_
genetics
Slide2Cell Theory of Inheritance
Plants and animals composed of cellsPlant cell – surrounded by cell wall
Animal cell – surrounded by cell membrane
Nucleus – location of chromosomes in cell
Chromosomes – carrier of genes
Slide3Chromosomes
Carriers of genetic material – genesOccur in pairs
Homologous chromosomes – members of a pair
Number of chromosomes constant among normal members of a species
Slide4Chromosome Number
Diploid (2N) numbersdonkey 62 horse 64
mule 63 swine 38
sheep 54 cattle 60
human 46 mink 30
dog 78 cat 38
chicken 78
Normal body cells have diploid (2N) number
Gametes (sperm and egg) have haploid (1N) number
Slide5Chromosomes
Two major types
Sex chromosomes – one pair which influences sex of organism
Autosomes – all pairs other than sex chromosomes
http://learn.genetics.utah.edu/content/begin/traits/karyotype/index.html
Slide6Sex Determination
MammalsSex chromosomes are:
female XX homogametic
male XY heterogametic
Chickens and turkeys
Sex chromosomes are:
female ZW heterogametic
male ZZ homogametic
Slide7Chromosomal Abnormalities
Changes in number of chromosomes (nondisjunction of sex cell)Aneuploidy – extra or missing chromosome(s)
Polyploidy – extra sets of chromosomes
Usually lethal in animals
Except aneuploidy of very small chromosomes (eg Down Syndrome in humans is extra #21)
Slide8Chromosomal Abnormalities
Changes in chromosome structure (see fig. 8.3, p. 143 illustration)
Deletion – piece of chromosome removed
Duplication – piece of homologous chromosome duplicated
Translocation – exchange of material between different (nonhomologous) chromosomes
Inversion – segment of chromosome reversed
Chromosomal Abnormalities
Changes in chromosome structure
Cause loss of fertility
Amount of loss dependent on type of change and importance of the affected segment of the chromosome
http://learn.genetics.utah.edu/content/begin/traits/karyotype/index.html
Slide10Cell Division
Two types
Mitosis – division of normal body cells
Meiosis – division of germinal cells to produce gametes (sperm and egg)
Slide11Cell Division
Mitosis
Cell division of normal body cells
Each daughter cell has same genetic complement as original cell
Slide12Cell Division
Mitosis
Four phases
Prophase
Metaphase
Anaphase
Telophase
Interphase – period between cell divisions
Slide13Cell Division
MeiosisDivision in germinal cells to produce sperm and egg
Each cell that results has 1N number of chromosomes (half of number of chromosomes in body cells
Slide14Cell Division
MeiosisTwo cycles of:
Prophase
Metaphase
Anaphase
Telophase
Results in four cells with 1N number
Slide15Cell Division
MeiosisDuring late prophase I
homologous chromosomes wrap together (synapsis)
Crossing over – exchange of genetic material between homologous chromosomes
Slide16Cell Division
MeiosisSpermatogenesis – meiotic production of sperm cells
Oogenesis – meiotic production of egg cells
Slide17Check It Out!
http://www.dnaftb.org/
Slide18The Gene
Component of DNA – deoxyribonucleic acid
Large double stranded polymer of units called nucleotides
Nucleotide
Sugar – deoxyribose
Phosphate group
Nitrogeneous base
adenine guanine
cytosine thymine
Slide19Transcription of RNA
Bases in DNA code for transcription of RNA
RNA – ribonucleic acid
Also nucleic acid
Single stranded
Uracil instead of thymine
Ribose instead of deoxyribose
Slide20RNA
Three primary types of RNA
Messenger RNA
Transfers code from DNA to protein synthesis
Transfer RNA
Carries amino acids to the ribosome
Ribosomal RNA
Forms part of the structure of the ribosome
Slide21Translation of RNA
RNA binds with ribosome
Ribosome is location of protein synthesis
Information on RNA used to generate amino acid sequence in proteins
Slide22Genetic Code
Each amino acid coded by a three base sequence (codon)
Most amino acids have more than one codon
One codon specifies beginning of a protein
Three codons specify the end of a protein
Slide23Control of Gene Function
Complete gene is actually a complex of different types of genes (complex called an operon)
Structural genes
Code for actual protein sequence
Regulatory genes
Affect function of the structural genes
Slide24Interactions Between Genes
EpistasisTwo or more gene pairs (not alleles) in which one gene pair influences expression of another gene pair – may or may not be on homologs
Example:
Horned, polled, scurred
Two gene pairs (horned vs polled) (smooth vs scurred)
If horned – scurred vs smooth does not matter
If polled – scurred vs smooth can express
Slide25Genes and Embryological Development
After union of sperm and eggCell division occurs
Early development - all cells are alike
Subsequent development – cells differentiate
Embryological development is genetically controlled
Slide26Genes and Embryological Development
Lethal genesGenes which stop development
Many must be received from both parents to cause death
Cause of high percentage of embryonic death
Slide27Biotechnology
BiotechnologyAll technologies that pertain to molecular manipulation of living material
Very difficult word to characterize
Genetic engineering
New methods for modifying the animal genome
Slide28Microbe Engineering
Recombinant DNA TechnologySegment of DNA removed from species of interest
Segment is inserted into a microorganism
Microorganism makes the product specified by the DNA
DNA is “recombined” into a new location
Slide29Recombinant DNA
Used for production of:Bovine growth hormone to increase milk production
Vaccines
Other pharmaceuticals
Bacteria to consume oil spills or other pollutants
Slide30Transgenesis
TransgenesisMovement of genes from one species into another
First use – development of mouse with extra genes for growth hormone
Slide31Genetic Engineering in Plants
Round-up-ready cropsSeveral crop species have been engineered to be resistant to the herbicide Round-up
Bt crops
Corn and cotton have genes from a microbe that causes them to be resistant to corn borer and boll weevil
Flavr-Savr tomato
Gene altered to lengthen shelf life
Slide32Cloning
Clone – genetic identicalIdentical twins are clones
Cloning by embryo splitting has been available for several years
Cloning from an adult DNA donor not possible until “Dolly”
Slide33Cloning
DollyDeveloped at Roslin Institute
Sheep cloned from cells from adult ewe mammary gland
Cells had to be “started over” to remove results of cell differentiation
Slide34Cloning
Potential uses for cloning in animalsLimited importance in routine livestock improvement
Combine with transgenesis to produce animals with unique genetic makeup
transgenesis to create first copy of animal with specific gene inserted
cloning to make multiple copies of that animal
Slide35Marker Assisted Selection
Current selection Based on actual traits measured in animals
Marker assisted selection
Based on identification of genetic markers that are associated with performance traits
Can be applied as soon as appropriate tissue (blood, skin etc) can be obtained
Shortens time to obtain information for choosing superior parents
Slide36Segregation and Recombination
Genes occur in pairs (except for those on sex chromosomes which are sex-linked)
The segregation of genes (in body cells) at one locus (gene location) is normally independent of the segregation of genes (in gametes) at another location (Principle of Independent Assortment)
Exception to this rule when genes are linked (on same chromosome)
Slide37Segregation and Recombination
LinkageGenes tend to be inherited together if close together on same chromosome
Linkage relationships are broken by crossing over (exchange between homologous chromosomes) during meiosis I, prophase I
Basis for idea of Marker Assisted Selection – if genetic marker is linked with gene for trait of interest, can select based on the marker
Slide38Mutation
Mutation – change in the base sequenceMay result in change in amino acid sequence in protein
May result in change in the phenotype
Change is usually detrimental (selection)
Only source of new genetic material
Slide39Phenotypic Expression of Genes
Phenotype = Genotype + Environment
Gene action varies among different genes
Dominance relationships vary widely
Slide40Phenotypic Expression of Genes
Dominant and recessive
Color in Angus
Genotype Phenotype
BB Black
Bb Black
bb Red
Black is dominant to red
Red is recessive
BB or bb – homozygous
Bb - heterozygous
Slide41Phenotypic Expression of Genes
Lack of dominance
Color in Shorthorns
Genotype Phenotype
RR Red
RW Roan
WW White
Both red and white are expressed in heterozygote
Slide42Phenotypic Expression of Genes
Additive
Each gene substitution (A for a, B for b) contributes the same amount (each A or B “adds” the same amount (absolute?)
Example: skin color in humans
Livestock examples in Ch 9
Contrast with non-additive types of gene action (dominance, epistasis)
Slide43Phenotypic Expression of Genes
Genetic control of almost all traits is some combination of additive and non-additive
Allows use of selection to improve herds through increasing frequency of desirable genes
Allows use of crossbreeding to maximize efficient combinations of genes
Slide44Sex-linked Inheritance
Some genes on the sex chromosomes
Inheritance pattern affected because males have only one X chromosome
Hemophilia in humans
Slide45Sex-influenced Inheritance
Inheritance that is affected by sex of individual
eg. scurs - dominant in males, recessive in females
eg. horns in sheep – dominant in males, recessive in females
Slide46Sex-limited Inheritance
Some traits express in only one sex
Female
Milk production, egg production, age at first estrus
Male
Scrotal circumference
Slide47Genome Project
Human Genome project Initiated by National Institutes of Health and Department of Energy
Large multi-year, multi-location project to map the human genome
Other genome projects
Cattle, sheep, swine, horses, dogs, cats, turkeys, chickens, mice and many other species