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Chapter 8 Section 3 Studying Heredity Objectives Predict the results of monohybrid genetic crosses by using Punnett squares. Apply a test cross to determine the genotype of an organism with a dominant phenotype. Predict the results of monohybrid genetic crosses by using probabilities. Analyze a simple pedigree.
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New Vocabulary Punnett square Test cross Probability pedigree
Sex-linked gene
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To predict the genotypes and phenotypes of offspring, Mendel ___________ his crosses and analyzed ________ amounts of data In 1905, a mathematician named Reginald ___________ devised a _______________ method, called a punnett square, for predicting the outcome of ________________ crosses controlled vast short hand Punnett individual
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Chapter 8 Punnett Squares
Section 3 Studying Heredity Punnett Squares A Punnett square is a diagram that predicts the outcome of a ______________ cross by considering all possible ___________ combinations of gametes in the cross. single allele
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segregate Female Y Y top Male y left y
Remember, the two alleles in a gene _________________ during gamete formation The possible gametes that the female can produce are written along the _________ of the square. The possible gametes that the male can produce are written along the _________ side of the square. segregate Female Y Y top Male y left y
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Each box inside the square is filled in with two letters obtained by ___________ the allele along the ______ of the box with the allele along the _________ of the box. Female combining top Male Yy Yy side Yy Yy
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What process is occurring in each box when the gametes combine?
fertilization
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What genotype will all of the possible offspring have?
And the phenotype? Yy yellow
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Practice! T t T TT Tt t Tt tt 1TT : 2Tt : 1tt 3 tall : 1 short
Cross a two pea plants heterozygous for height… T = tall and t = short Genotype ratio? Phenotype ratio? T t T TT Tt t Tt tt 1TT : 2Tt : 1tt 3 tall : 1 short
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Practice! Y y y Yy yy y Yy yy 2Yy : 2yy 2 yellow : 2 green
Cross a “female” pea plant heterozygous for seed color and a “male” recessive for seed color… Y = yellow and y = green Genotype ratio? Phenotype ratio? Y y y Yy yy y Yy yy 2Yy : 2yy 2 yellow : 2 green
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Reduce the ratio 2:2 Convert this ratio to a fraction What percent does the fraction represent? 1 : 1 50%
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The previous crosses were for genes on _________________ chromosomes
Review…what are autosomes? Punnett squares can also be created for ________ chromosomes In this case, the alleles must be linked on the _______ or _______ chromosome autosomal Your 1st 22 homologous pairs of chromosomes sex X Y
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Morgan In 1910, Thomas Hunt __________ discovered sex-linked inheritance while studying _______ ________. In fruit flies, the gene for eye color is linked on the ______ chromosome If R = red and r = white, determine the eye color and sex for the following genotypes XRXR = ________________ XRXr = _________________ XrXr = __________________ XRY = __________________ XrY = __________________ fruit flies X Red female Red female White female Red male White male
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In humans, red green color blindness is a _____________ trait linked on the _____ chromosome
Determine the following phenotypes… XCXc = _______________ XcY = ________________ XCY = ________________ The female above does not have color blindness but ____________ the recessive allele recessive X Color vision female Color blind male Color vision male carries
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Practice! XC Xc Xc XCXc XcXc XCY XcY Y 1 XCXc : 1 XcXc : 1 XCY : 1 XcY
Cross a female who is a carrier for colorblindness with a male recessive for color blindness C = normal vision and c = colorblind Genotype ratio? Phenotype ratio? Does a male offspring inherit colorbindness from his mom or dad? Xc XCXc XcXc XCY XcY Y 1 XCXc : 1 XcXc : 1 XCY : 1 XcY 1 c.v. female : 1 c.b. female : 1 c.v. male : 1 c.b. male Mom!...inherits Y from dad
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Review? What genotype(s) may a purple pea plant have?
Animal breeders, horticulturists, and others involved in breeding organisms often need to know whether an organism with a dominant phenotype is _______________ or ________________ for a trait. To determine the genotype, breeders cross the organism with an individual that is _____________ for the trait in a cross called a ________ cross PP or Pp homozygous heterozygous recessive test
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Test cross P P P p p p p p Pp pp Pp Pp Pp Pp Pp pp
If the unknown genotype is PP, what color flowers will all of the offspring have? If the unknown genotype is Pp, what color flowers may the offspring have? Purple Purple and white
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Chapter 8 Outcomes of Crosses # of outcomes # of outcomes
Section 3 Studying Heredity Outcomes of Crosses Like Punnett squares, ______________ calculations can be used to predict the results of genetic crosses. Probability is the _________________ that a specific event will occur. Probability = probability likelihood # of outcomes desired # of outcomes total
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So if there are five marbles in a jar, and only one is red, what is the probability that you pull a red marble out of the jar? If you flip a coin, what is the probability that it will land heads up? If you flip a coin again, what is the probability that it will lands head up? 1/5 1/2 1/2
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future X X X XX XX Y XY XY 1/2 1/2
So prior events do not affect the outcome of ____________ events In the following cross… What is the probability that two parents will have a girl? What is the probability that their next child will be a girl? X X X XX XX Y XY XY 1/2 1/2
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The outcomes predicted by Punnett squares are most often seen in ______________ populations….
Is everyone’s family made up of exactly half girls and half boys? But a larger population, like the entire _________, is roughly 50:50 or 1:1 large no planet
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multiple To determine the probability of ____________ events or events occurring at the _________ time, the probability for each event is _________________ by eachother. What is the probability that a coin will land heads up four times consecutively? same multiplied ½ x ½ x ½ x ½ = 1/16
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P p P PP Pp p Pp pp T t T TT Tt t Tt tt 3/4 3/4 ¾ x ¾ = 9/16
What is the probability that a pea plant offspring will have purple flowers? What is the probability that a pea plant offspring will be tall? What is the probability that a pea plant offspring will have purple flowers and tall height? P PP Pp 3/4 p Pp pp 3/4 T t T TT Tt t Tt tt ¾ x ¾ = 9/16
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Chapter 8 Inheritance of Traits
Section 3 Studying Heredity Inheritance of Traits Geneticists often prepare a ________________, a family history that shows how a trait is inherited over _____________ generations. Pedigrees are particularly helpful if the trait is a genetic _______________ and the family members want to know if they are _____________ or if their _________________ might get the disorder. By analyzing a pedigree, we can determine if a trait is ______________ or ______ - linked and ____________ or ______________ pedigree several disorder carriers children autosomal sex dominant recessive
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Female = circle Male = square Horizontal Line = mating Vertical line = offspring Shaded = affected by the trait Diagonal line = death from trait
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Autosomal recessive Aa Aa aa recessive two carrier Aa or AA
Most genetic disorders are caused by _____________ alleles In this situation, an offspring with ______ recessive alleles has the trait, while each parent is a _________________ What allele combinations might have the other two offspring have? Aa Aa recessive aa two carrier Aa or AA
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Autosomal Dominant aa aa Aa aa
If a trait is dominant, an affected individual will have at least ______ parent who also has the _____________ trait Is the female parent homozygous dominant or heterozygous? How do you know? aa Aa one aa Aa aa dominant heterozygous Not all of the offspring inherit a dominant allele
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Sex-linked XcY XcY XCXc males XCXc Y female
If a trait is sex-linked, it will appear more often in ________ than in females What genotype must all of the females have? What chromosome does a male parent pass onto his son? So is the recessive X-linked gene inherited from the male or female parent? XcY XCXc males XcY XCXc Y female
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Objective 1 T t t t Tt tt Tt tt 2Tt : 2tt 2 tall : 2 short
Predict the results of monohybrid genetic crosses by using Punnett squares. If T = tall and t = short… Genotype ratio? Phenotype ratio? T t t Tt tt t Tt tt 2Tt : 2tt 2 tall : 2 short
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Objective 2 t t Tt Tt Dominant Genotype? tt tt T t
Apply a test cross to determine the genotype of an organism with a dominant phenotype. t t Tt Tt T Dominant Genotype? tt tt t
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Objective 3 T t T TT Tt t Tt tt
Predict the results of monohybrid genetic crosses by using probabilities. If T = tall and t = short, what is the probability that an offspring will inherit short height? T t T TT Tt t Tt tt 1/4
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Objective 4 Analyze a simple pedigree. Does this pedigree
show an autosomal dominant, autosomal recessive, or sex- linked trait? Autosomal recessive
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