BIOL 101 Guided Reading Questions GRQs Complete and submit this GRQ as a PDF before lecture and before your online Mastering Assignment L11 GRQs Patterns of Inheritance I Reading Objectives Define and use the terms that geneticists use to communicate about inheritance Construct Punnett squares to examine the offspring that arise from independent segregation within parents for autosomal and sex linked traits Determine the types of gametes that form through independent assortment in a dihybrid and link this to metaphase I of meiosis Explain why a tester is a useful tool in genetic crosses Module 9 2 The science of genetics began in an abby garden 1 What made the pea plant a good model for studying genetics as opposed to say humans they have easily observable traits reproduce quickly and can be easily controlled for cross pollination They also produce many offspring and are capable of both self pollination and cross pollination 2 One important aspect for Mendel was that he had pea plants that could breed true what does this mean For example if a plant was a purebreeding purple flower plant what does this indicate about the plant s two alleles that code for flower color homozygous for a trait meaning that it has two identical alleles for that trait For a purebreeding purple flower plant this indicates that both alleles for flower color are the same PP or pp depending on the dominant or recessive trait Module 9 3 Mendel s law of segregation describes the inheritance of a single character 1 Take time to be sure you know the bold faced terms You need a good understanding of these terms to speak like a geneticist List here any that you are not already familiar with and define them These terms should become more obvious as you start applying them in the next section too The law of segregation is useful to predict how alleles for one character will segregate into gametes 2 What type of gametes can a parent that is homozygous dominant PP make through meiosis A homozygous dominant PP parent can only produce gametes with the dominant allele P 3 What type of gametes can a parent that is homozygous recessive pp make through meiosis BIOL 101 Guided Reading Questions GRQs Complete and submit this GRQ as a PDF before lecture and before your online Mastering Assignment A homozygous recessive pp parent can only produce gametes with the recessive allele p 4 What type of offspring will they make if the gametes of these two parents fuse through fertilization All offspring will be heterozygous Pp and exhibit the dominant phenotype 5 Practice constructing a Punnett square when a purple heterozygote Pp is crossed to another purple heterozygote Pp What will be the phenotypes of the offspring and in what ratio will they be to each other Phenotypes 3 purple flowered plants PP Pp Pp 1 white flowered plant pp Phenotypic ratio 3 1 Module 9 4 Homologous chromosomes bear the alleleles for each other 1 What is similar about homologous chromosomes What might be different Does a drawing help you here Similar Homologous chromosomes have the same genes in the same locations loci Different They may carry different alleles for the same gene e g one may carry a dominant allele and the other a recessive one Module 9 5 The law of independent assortment is revealed by tracking two characters at once 1 Mendel used single gene or monohybrid experiments to describe his law of segregation He used characters or dihybrid experiments to come up with what law law of independent assortment 2 When an organism that is heterozygous for two genes RrYy is crossed to another organism that is the same genotype RrYy the phenotypic ratio will always be what Dihybrid x dihybrid 9 3 3 1 3 What fraction will have the dominant phenotype for both traits 9 16 4 What fraction will have the dominant phenotype for trait A and be recessive for B 3 16 5 What fraction will have the dominant phenotype for trait B and be recessive for a 3 16 6 What fraction will have the recessive phenotype for both traits 1 16 BIOL 101 Guided Reading Questions GRQs Complete and submit this GRQ as a PDF before lecture and before your online Mastering Assignment 7 Using the traits in Labradors discussed in the book predict the phenotype of offspring obtained by mating a black Lab homozygous for coat color and normal vision with a chocolate Lab that is blind from PRA All offspring will have black coats and normal vision if black is dominant and PRA blindness is recessive Module 9 6 Geneticists can use a testcross to determine unknown genotypes 1 What is a testcross useful for determine the genotype of an individual with a dominant phenotype whether it is homozygous dominant or heterozygous 2 What is the genotype of one of the individuals that is always crossed in a testcross We call this individual a tester Homozygous recessive Module 9 7 Mendel s laws reflect the rules of probability 1 Use the rule of multiplication what is the chance that a woman who is pregnant four different times will give rise to a family with four sons 1 16 using the rule of multiplication 1 2 chance for a boy each time multiplied across four pregnancies 2 Apply the rule of addition to a single gene Punnett square when Bb x Bb What fraction of offspring at heterozygotes See Fig 9 7 1 2 Module 9 20 Chromosomes determine sex in many species 1 How many autosomes are in the human male 44 Sex chromosomes 2 XY 2 How many autosomes are in the human female 44 Sex chromosomes 2 XX 3 How is it possible that a baby is born with the XY chromosomes but has ovaries This example illustrates a complexity of defining biological sex simply by XY chromosomes This could occur due to a mutation in the SRY gene which is responsible for male sex development leading to the development of ovaries despite the presence of XY chromosomes Module 9 21 Sex linked genes exhibit a unique pattern of inheritance 1 White eyes is an x linked recessive trait in fruit flies A female fruit fly that is heterozygous is crossed with a red eyed male What are the possible offspring Set up a Punnett square What if the male was white eyed instead Use Figure 9 21 to check your understanding after you try this BIOL 101 Guided Reading Questions GRQs Complete and submit this GRQ as a PDF before lecture and before your online Mastering Assignment Half of the female offspring will be red eyed homozygous or heterozygous and half of the male offspring will be red eyed If the male is white eyed instead the male offspring will be 50 white eyed and 50 red
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