1221 x 1221 how many different genotype for the f2

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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...
View Full Document

This note was uploaded on 01/16/2014 for the course LIFESCI 4 taught by Professor Ribaya during the Spring '08 term at UCLA.

Ask a homework question - tutors are online