Fundamental Principles of Genetics (Chapter 8) - PowerPoint Presentation

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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

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Cell 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

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Chromosomes

Carriers of genetic material – genesOccur in pairs

Homologous chromosomes – members of a pair

Number of chromosomes constant among normal members of a species

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Chromosome 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

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Chromosomes

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

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Sex Determination

MammalsSex chromosomes are:

female XX homogametic

male XY heterogametic

Chickens and turkeys

Sex chromosomes are:

female ZW heterogametic

male ZZ homogametic

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Chromosomal 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)

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Chromosomal 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

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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

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Cell Division

Two types

Mitosis – division of normal body cells

Meiosis – division of germinal cells to produce gametes (sperm and egg)

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Cell Division

Mitosis

Cell division of normal body cells

Each daughter cell has same genetic complement as original cell

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Cell Division

Mitosis

Four phases

Prophase

Metaphase

Anaphase

Telophase

Interphase – period between cell divisions

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Cell 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

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Cell Division

MeiosisTwo cycles of:

Prophase

Metaphase

Anaphase

Telophase

Results in four cells with 1N number

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Cell Division

MeiosisDuring late prophase I

homologous chromosomes wrap together (synapsis)

Crossing over – exchange of genetic material between homologous chromosomes

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Cell Division

MeiosisSpermatogenesis – meiotic production of sperm cells

Oogenesis – meiotic production of egg cells

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Check It Out!

http://www.dnaftb.org/

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The 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

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Transcription 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

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RNA

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

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Translation of RNA

RNA binds with ribosome

Ribosome is location of protein synthesis

Information on RNA used to generate amino acid sequence in proteins

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Genetic 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

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Control 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

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Interactions 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

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Genes 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

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Genes 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

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Biotechnology

BiotechnologyAll technologies that pertain to molecular manipulation of living material

Very difficult word to characterize

Genetic engineering

New methods for modifying the animal genome

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Microbe 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

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Recombinant DNA

Used for production of:Bovine growth hormone to increase milk production

Vaccines

Other pharmaceuticals

Bacteria to consume oil spills or other pollutants

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Transgenesis

TransgenesisMovement of genes from one species into another

First use – development of mouse with extra genes for growth hormone

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Genetic 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

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Cloning

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”

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Cloning

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

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Cloning

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

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Marker 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

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Segregation 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)

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Segregation 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

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Mutation

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

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Phenotypic Expression of Genes

Phenotype = Genotype + Environment

Gene action varies among different genes

Dominance relationships vary widely

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Phenotypic 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

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Phenotypic 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

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Phenotypic 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)

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Phenotypic 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

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Sex-linked Inheritance

Some genes on the sex chromosomes

Inheritance pattern affected because males have only one X chromosome

Hemophilia in humans

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Sex-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

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Sex-limited Inheritance

Some traits express in only one sex

Female

Milk production, egg production, age at first estrus

Male

Scrotal circumference

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Genome 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