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Unit B Unit B Understanding Animal Understanding Animal

Body SystemsBody Systems

Lesson 8 Lesson 8 Understanding Animal Understanding Animal

GeneticsGenetics

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TermsTerms

AllelesAlleles ChromosomeChromosome Co dominanceCo dominance CrossoverCrossover Deoxyribonucleic Deoxyribonucleic

acidacid DNADNA DominantDominant Genetic codeGenetic code

GenomeGenome GenotypeGenotype HeredityHeredity HeritabilityHeritability Heritability estimateHeritability estimate HeterozygousHeterozygous HomozygousHomozygous Incomplete Incomplete

dominancedominance

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Terms Cont. Terms Cont.

LinkageLinkage MutationMutation PhenotypePhenotype ProbabilityProbability Punnett SquarePunnett Square

Qualitative traitsQualitative traits Quantitative traitsQuantitative traits RecessiveRecessive Sex chromosomesSex chromosomes

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Why is it important for a livestock Why is it important for a livestock producer to understand genetics?producer to understand genetics?

The study of genetics is concerned with the The study of genetics is concerned with the transfer of traits. transfer of traits.

Gregor Mendel discovered that these traits are Gregor Mendel discovered that these traits are inherited through units called genes. Genes inherited through units called genes. Genes were found in pairs and half of the inherited were found in pairs and half of the inherited traits come from the father and half from the traits come from the father and half from the mother. mother.

This passing of traits from parents to offspring This passing of traits from parents to offspring is called is called heredityheredity. Not all differences in . Not all differences in animals are caused by genetics. Some are animals are caused by genetics. Some are caused by the conditions under which the caused by the conditions under which the animal is raised.animal is raised.

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Importance of GeneticsImportance of Genetics

A A chromosomechromosome is a is a tiny threadlike part in tiny threadlike part in a cell that contains a cell that contains the genetic material the genetic material found in the nucleus.found in the nucleus.

The genetic material The genetic material found in the found in the chromosomes is called chromosomes is called the the genomegenome of the of the organism.organism.

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Importance of GeneticsImportance of Genetics Chromosomes are made of Chromosomes are made of

genes that consist of DNA. genes that consist of DNA. DNA DNA is a protein-like nucleic acid on is a protein-like nucleic acid on genes that controls inheritance. genes that controls inheritance.

Each DNA molecule consists of Each DNA molecule consists of two stands shaped as a double two stands shaped as a double helixhelix

There are 4 nitrogen bases There are 4 nitrogen bases found in DNA. They are: found in DNA. They are: cytosine, guanine, adenine, and cytosine, guanine, adenine, and thymine. thymine.

The The genetic codegenetic code is the is the sequence of nitrogen bases in sequence of nitrogen bases in the DNA molecule. Replicating the DNA molecule. Replicating itself allows for the molecule to itself allows for the molecule to pass genetic information from pass genetic information from one cell generation to the next.one cell generation to the next.

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How do genotype and phenotype How do genotype and phenotype differ?differ?

GenotypeGenotype is the actual genetic is the actual genetic code. It controls physical and code. It controls physical and performance traits. The genotype of performance traits. The genotype of an organism cannot be changed by an organism cannot be changed by environmental factors.environmental factors.– Genetics sounds like Genotype!Genetics sounds like Genotype!

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PhenotypePhenotype is the organism’s is the organism’s physical or outward appearance. This physical or outward appearance. This is the part of the genotype the is the part of the genotype the organism expresses or shows. In organism expresses or shows. In some instances, phenotype may be some instances, phenotype may be altered by the organism’s altered by the organism’s environment.environment.– Phenotype sounds like Phenotype sounds like

Physical Traits!Physical Traits!

How do genotype and How do genotype and phenotype differ?phenotype differ?

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A A homozygoushomozygous organism is one organism is one having similar having similar allelesalleles or genes on or genes on the DNA molecule for a particular the DNA molecule for a particular trait. trait.

While a While a heterozygousheterozygous organism is organism is one having different alleles for a one having different alleles for a particular trait.particular trait.

How do genotype and How do genotype and phenotype differ?phenotype differ?

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How can I estimate which traits will How can I estimate which traits will be inherited by offspring?be inherited by offspring?

Estimating is based on probability. Estimating is based on probability. ProbabilityProbability is the likelihood or chance is the likelihood or chance that a trait will occur.that a trait will occur.

Mating animals of particular traits does not Mating animals of particular traits does not guarantee that the traits will be expressed guarantee that the traits will be expressed in offspring. in offspring.

HeritabilityHeritability is the proportion of the total is the proportion of the total variation (genetic and environmental) that variation (genetic and environmental) that is due to additive gene effects.is due to additive gene effects.

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A A heritability estimateheritability estimate expresses expresses the likelihood of a trait being passed the likelihood of a trait being passed on from parent to offspring. If a trait on from parent to offspring. If a trait has a high heritability, the offspring has a high heritability, the offspring are more likely to express that same are more likely to express that same traittrait

How can I estimate which traits How can I estimate which traits will be inherited by offspring?will be inherited by offspring?

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Heritability Estimates for Beef CattleHeritability Estimates for Beef CattleExamples of TraitsExamples of Traits

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HeritabilityHeritability The genes contained in an animal control The genes contained in an animal control

traits of that animal. Some traits are traits of that animal. Some traits are controlled by only one pair of genes, while controlled by only one pair of genes, while others require several pairs.others require several pairs. – Qualitative traitsQualitative traits are traits controlled only by are traits controlled only by

a single pair of genes & cannot be altered by a single pair of genes & cannot be altered by the environment. Their phenotype is either one the environment. Their phenotype is either one thing or the other. For example, either black or thing or the other. For example, either black or white. These traits most easily show how genes white. These traits most easily show how genes are inherited. An example is coat color.are inherited. An example is coat color.

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Quantitative traitsQuantitative traits are traits are traits controlled by several pairs of genes. controlled by several pairs of genes. These traits are expressed across a These traits are expressed across a range. These traits can also be range. These traits can also be altered by environment. Examples altered by environment. Examples include rate of gain, growth rate, include rate of gain, growth rate, back fat depth, etc.back fat depth, etc.

HeritabilityHeritability

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Not all traits contained within an Not all traits contained within an organism are expressed. organism are expressed. – DominantDominant traits cover up or mask the traits cover up or mask the

alleles for alleles for recessiverecessive traits. In some traits. In some organisms there are cases of organisms there are cases of co- co- dominancedominance of traits in which both of traits in which both dominant and recessive genes are dominant and recessive genes are expressed. expressed. Incomplete dominanceIncomplete dominance happens when a blending of the allele pair happens when a blending of the allele pair is expressed.is expressed.

HeritabilityHeritability

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The The Punnett SquarePunnett Square is a technique is a technique for predicting genotype. It considers for predicting genotype. It considers the dominant and recessive genes of the dominant and recessive genes of the male and female parents for one the male and female parents for one trait.trait.

HeritabilityHeritability

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Estimating the Heritability of Certain Estimating the Heritability of Certain TraitsTraits

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Estimating the Heritability of Certain Estimating the Heritability of Certain TraitsTraits

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Sex Determination, Linkage, Crossover, and Sex Determination, Linkage, Crossover, and MutationMutation

There are several other factors that There are several other factors that are important for livestock producers are important for livestock producers to understand.to understand.– Sex determinationSex determination—Determination of the —Determination of the

sex of zygote depends on the sex of zygote depends on the sex sex chromosomeschromosomes..

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Sex DeterminationSex Determination

MammalsMammals—Male sex —Male sex chromosomes are either X chromosomes are either X or Y. A zygote that receives or Y. A zygote that receives a Y chromosome from a Y chromosome from sperm will be male and a sperm will be male and a zygote that receives an X zygote that receives an X chromosome from sperm chromosome from sperm will be female. The male will be female. The male makes sex determination as makes sex determination as all eggs from female all eggs from female receive an X chromosome.receive an X chromosome.– Therefore, a female zygote will Therefore, a female zygote will

have two X chromosomes (XX) have two X chromosomes (XX) while a male zygote will have one while a male zygote will have one X and one Y chromosome (XY).X and one Y chromosome (XY).

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Sex DeterminationSex Determination PoultryPoultry—The female determines the —The female determines the

sex of the offspring. The male carries sex of the offspring. The male carries two sex chromosomes (ZZ). The two sex chromosomes (ZZ). The female carries only one sex female carries only one sex chromosome (ZW). After meiosis, all chromosome (ZW). After meiosis, all the sperm cells carry a Z the sperm cells carry a Z chromosome. Only half of the egg chromosome. Only half of the egg cells carry a Z chromosome; the other cells carry a Z chromosome; the other half carries a W chromosome.half carries a W chromosome.

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LinkageLinkage The tendency for certain The tendency for certain

traits to appear in groups traits to appear in groups in the offspring is called in the offspring is called linkagelinkage..

Early studies in genetics Early studies in genetics were based on the idea were based on the idea that all genes are that all genes are redistributed in each redistributed in each mating. It was found, mating. It was found, however, that some groups however, that some groups of traits seemed to stay of traits seemed to stay together in the offspring.together in the offspring.

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CrossoverCrossover

CrossoverCrossover is the is the formation of new formation of new chromosomes resulting chromosomes resulting from the splitting and from the splitting and rejoining of the original rejoining of the original chromosome. This forms chromosome. This forms new chromosomes with new chromosomes with different combinations different combinations of genes.of genes.

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MutationMutation

Mutation Mutation is the appearance of a is the appearance of a new trait in the offspring that did not new trait in the offspring that did not exist in the genetic makeup of the exist in the genetic makeup of the parents.parents.

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Review/ SummaryReview/ Summary

How are genotypes and phenotypes How are genotypes and phenotypes different? different?

How is heritability estimated in How is heritability estimated in animals?animals?

What happens during crossover and What happens during crossover and mutation? mutation?