Download - Principles and Patterns of Inheritance
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• I.History of Genetics• Genetics - the scientific study of
inheritance • The domestication of dogs is one of the
earliest human experiences with genetics.• Millions of years ago there were no dogs.• Today’s domestic dogs are descended
from a wolf ancestors
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• Ancient people selected traits to be passed from generation to generation.
• Trait - a characteristic that can be
passed from parent to offspring
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• It has not always been understood how traits are passed from parent to offspring.
• For many centuries scientists believed that traits were blended in offspring, they would later learn that this idea was incorrect.
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• Review:• during cell division chromosomes
are replicated and distributed to daughter cells during meiosis.
• The traits that are passed from parents to offspring are in these chromosomes
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• II.Gregor Mendel• Clues to
understanding inheritance came from an Austrian monk, Gregor Mendel, in the 1860’s.
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• He used pea plants to study how traits were passed from one generation to the next.
• Mendel gathered detailed information on more than 20,000 pea plants over an eight year period.
• He applied mathematics and statistics to his findings and found that they did not support the blending hypothesis.
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• III. Mendel’s Experiments• Mendel chose to work with the pea
plant for several reasons:1. the structure of the pea plant- the pea flower petals make it very easy for the pollen from the anther from a plant to fertilize it’s own pistil.
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• This produced a purebred offspring.
purebred offspring - receives the same genetic traits from both parents
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• Mendel was also able to transfer pollen from one plant to another by hand. This produced a hybrid.
• hybrid offspring - receives different forms of a genetic trait from each parent
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2. Presence of distinctive traits
Mendel studied several traitsEach of the traits had two
distinct forms
ex. pea pods are either yellow or green, there is no intermediate
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3. Rapid reproduction cycle
This allowed Mendel to repeat his experiments many times to test his results
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• IV. Mendel’s ObservationsMendel began his experiments using two different groups of inbred plants. He called this the parents (or P) generation.
yellow pea x green pea
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• He called the offspring of that mating the first filial generation or F1 generation.
100%yellow pea plants • Mendel let the F1 plants self fertilize to
produce the F2 generation. 75% of the F2offpsring produced
were yellow while 25% were green.(3:1 ratio)
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• V. Mendel’s Conclusions• Mendel’s experiments showed that
the blending hypothesis was wrong.
• Mendel hypothesized that each trait is controlled by a distinct “factor”
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• We now know that Mendel’s “factors” are genes.
• Gene - a section
of a chromosome that codes for a particular trait.
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• Alleles - different forms of a gene (ex. yellow, green in peas) Alleles are represented by letters ex. Y=yellow, y= green
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• dominant allele - form of the gene that is expressed fully when two different alleles are present
• recessive allele - form of the gene not expressed when two different alleles are present.
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• Letters are used to represent alleles:
the dominant traits is represented by an uppercase letter ex.Y
• the recessive allele is represented
by a lower case letter ex.y
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• Mendel published his work in 1866, his work went unrecognized for 37 years.
In 1903, Walter S.Sutton used a microscope and observed that chromosomes behaved like Mendel’s factors.
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genesChromosome
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• VI. Genes Affect Traits • GENOTYPE - the genetic make up of an
organism. The genotype includes both genes in a pair of homologous chromosomes.
• genotype of purebred yellow peas is YY• genotype of hybrid yellow peas is Yy• genotype of green peas_______
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• PHENOTYPE - the outward expression of a trait
• phenotype for F1 generation of peas is yellow
Green seeds Yellow seeds
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• If the two alleles of the gene are the same they are called homozygous. ex. YY, yy
• If the two alleles of the gene are different they are called heterozygous ex.Yy
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• VII. Mendel’s Laws• The basic rules of inheritance are
called Mendel’s Laws• Law of Segregation - each pair of
genes segregates and ends up in gametes during meiosis
• half an organisms gametes contain one chromosome from a homologous pair, the other half contain the other chromosome
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• Law of Independent Assortment - gene pairs separate into gametes randomly and independently of one another.
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• Law of Dominance - recessive allele is expressed only when the organism has no copy of the corresponding dominant allele
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• IX. Genetic InteractionsComplete dominance – the dominant allele masks the recessive allele
Recessive trait : Sugary kernels shown only when no dominant allele is present
Dominant trait: Yellow kernels
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• incomplete dominance - when two different alleles for the same trait combine the offspring is an intermediate ex.red snap dragon x white snap dragon = pink snap dragon
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• codominance - both alleles in the heterozygote express themselves fullyex. blood type
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• Polygenic Traits - traits affected by more than one gene.
ex. eye color, skin color
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• X. Probability• fractions, percentages, or ratios used to
predict the likelihood of an outcome, you are measuring probability.
• When you flip a coin, you can get either heads or tailsThe probability of getting heads is 1/2, 50%, 1:1
• Scientists can use probability to predict the outcome of breeding experiments.
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