1221 x 1221 how many different genotype for the f2

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Unformatted text preview: Monohybrid cross F2 phenotypic ratio Test cross phenotypic ratio Two traits (two genes) 9:3:3:1 1:1:1:1 Dihybrid cross F2 phenotypic ratio Test cross phenotypic ratio what is the genotypic ratio of the F2 generation? 1:2:2:1 x 1:2:2:1 How many different genotype for the F2 generation? 9 because they are independently assorted, 3 genotypes from R and 3 from Y. Summary • A particular trait (phenotype) is determined by a factor (Gene). • There are two forms of this factor (alleles). • Principle of dominance: When T and t co-exist in a plant, one observes the T phenotype. T: dominant t: recessive • Principle of segregation: The two alleles, T and t, separate (segregate) during gamete formation, then unite at random, one from each parent, at fertilization. • Principle of independent assortment: The alleles of different genes segregate (assort) independently during gamete formation. V. Human Pedigrees Family Pedigrees Dominant Traits Pedigree analysis: a tool to study human genetics • Mendel’s principles apply to the inheritance of many human traits -Rare traits can be studied by carefully analyzing families that are affected. In other words, the trait may be rare in the population but common in a particular family. Recessive Traits Freckles No freckles Widow’s peak Straight hairline Free earlobe Attached earlobe Family Pedigree female male affected individual mating offspring Fetus or sex unspecified • Filled, means affected, open means unaffected (normal). Family Pedigree • Shows the history of a trait in a family • Allows researchers to analyze human traits Female Dd Joshua Lambert Dd Abigail Linnell D_ Abigail Lambert D_ John Eddy Dd dd Dd Dd Deaf Hearing carrier: person with one copy of the allele for a recessive disorder and does not exhibit symptoms Dd Elizabeth Eddy dd Jonathan Lambert Dd D_ Hepzibah Daggett Male Dd dd Important assumption for now: When a trait is rare, and there is a random mating, you can assume that a person who marries into the affected family is not a carrier. Human Disorders Controlled by a Single Gene •  Many human traits show simple inheritance patterns and are controlled by genes on autosomes (chromosomes other than sex chromosomes X & Y). Autosomal Dominant T raits Polydactyly • Dominant human genetic disorder; affected individuals have extra digits •  In some cases, affected child may have unaffected parents (incomplete penetrance). Autosomal Dominant T raits How can one look at a pedigree and tell that the disease is caused by a dominant gene? • Affected individual always has an affected parent. • Usually, affected individuals appear in every generation. • Heterozygotes show phenotype. • Affected parents pass the phenotype to both sons and daughters. Pink: affected Blue: normal Sample Problem aa aa aa aa aa aa aa Aa aa aa aa Aa Aa aa aa aa aa aa aa aa aa Aa Aa Aa aa aa ? 1/2 1. Assign the genotypes to all individuals, left top to bottom right, with Aa, etc. 2. Probability that diamond will be affected? Autosomal Recessive T raits Au...
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