Mendel s Laws of Genetic Inheritance How to explain genetic inheritance o a family group photograph illustrating the passage of hereditary information from one generation to the next o the three children resemble one another and their parents more closely that they resemble other humans because they inherit their particular genes from their parents o the cat shares many features with the humans but during millions of year of evolution that have separated humans and cats we both have accumulated many hereditary changes that now make us quite different species Gregor Mendel 1822 884 o from monohybrid cross Mendel deduced that Genetic characters are controlled by unit factors that exist in pairs When two unlike factors for a single trait co exist in an individual one factor is dominant to the other recessive Principle of segregation During the formation of gametes the paired factors separate or segregate randomly so that each gamete receives one or the other factor with equal likelihood Mendel s Principle of Independent Assortment o During the formation of gametes segregating pairs of unit factors assort independently of each other o Important to realize that when two or more events occur independently the probability of both events occurring together is the PRODUCT of the chances of each event occurring along example tossing coins Analysis of monohybrid cross where one trait is followed o true breeding the same traits will show up thought generations DD Tall plant dd short plant ex having a self breeding DD plant self pollinate and it will be true breeding for DD plants DD x dd Dd Dd x Dd DD Dd Dd dd genotypic ratio is 1 2 1 phenotypic ratio is 3 1 QUESTION What is the genotypic ratio of offspring if I cross two heterozygous flies with wings Ww x Ww ANSWER 1 2 1 or 1 WW 2Ww and 1ww QUESTION What is the genotypic ratio of offspring if I cross a heterozygous fly with wings with a wingless fly Ww x ww ANSWER 1 1 or 2WW and 2ww Analysis of dihybrid cross o Where two traits are followed o usually parents are true breeding and yellow and round are dominant to wrinkled and green yellow round x green wrinkled yellow wrinkled x green round all yellow round yellow round x yellow round 9 16 yellow round 3 16 green round 3 16 yellow wrinkled 1 16 green wrinkled Product law of probabilities o When two independent events occur simultaneously the combined probability of the two outcomes is equal to the product of their individual probabilities of occurrence o Can see when generating a phenotypic ratio using the forked line method o Determine the probability that a plant of genotype CcWw will be produced from parental plants of genotypes CcWw and Ccww o calculate the individual probabilities of obtaining the separate outcomes Cc and Ww Cc x Cc 1 4 CC 1 2 Cc 1 4cc Ww x ww 1 2 Ww 1 2 ww p 1 2 Cc 1 2 Ww 1 4 CcWw QUESTION What are the odds of throwing heads five times in a row ANSWER 1 2 x 1 2 x 1 2 x 1 2 x 1 2 or 1 in 2 5 Product law of probabilities forked line method example o F1 generation yellow round x yellow round 3 4 are yellow are green are round and are wrinkled are round and are wrinkled 9 16 yellow round 9 16 yellow wrinkled 3 16 green round 1 16 green wrinkled Analysis of dihybrid cross o P1 cross P1 cross GGWW yellow round and ggww green wrinkled GGww yellow wrinkled x ggWW green round F1 generation GgWw yellow round in both cases GgWw x GgWw 8 yellow round 3 yellow wrinkled 3 green round and 1 green wrinkled QUESTION What are the F2 genotypic and phenotypic ratios if you cross a wingless red eyed fly wwRR with a winged white eyed fly WWrr ANSWER 9W R 3W rr 3wwR 1wwrr Genetic Pedigree Analysis o notation for pedigree analysis circle female square male diamond sex unknown affected individuals are always shaded one horizontal line connecting a circle and a square parents a double horizontal line connecting a circle and a square consanguineous parents related a horizontal line with vertical lines extending to with squares and circles attached to them offspring in birth order Genetic Pedigree Analysis o recessive traits typically skip generations o recessive autosomal traits appear equally in both sexes