Chapter 3 Lecture Concepts of Genetics Tenth Edition Mendelian Genetics

Mendel and his peas Mendel put forth the basic principles of inheritance, publishing his findings in The significance of his work did not become widely known until © 2012 Pearson Education, Inc.

Monohybrid Crosses Reveal: Mendel's first three postulates Unit factors in pairs –Genetic characters are controlled by unit factors existing in pairs in individual organisms Dominance/Recessiveness –In the pair of unit factors for a single characteristic in an individual, one unit factor is dominant and the other is recessive Segregation –The paired unit factors segregate (separate) independently during gamete formation

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A Punnett square allows the genotypes and phenotypes resulting from a cross to be visualized easily

© 2012 Pearson Education, Inc. Figure 3.3

Now Solve This: 3-1 pg 47 © 2012 Pearson Education, Inc.

The test cross: One character A testcross is a way to determine whether an individual displaying the dominant phenotype is homozygous or heterozygous for that trait

© 2012 Pearson Education, Inc. Figure 3.4

Probability as a tool in genetics Express the likelihood of the occurrence of a particular event Have to know something about how the vent takes place or how often it takes place. The multiplication rule – probability of two or more independent events taking place together is calculated by multiplying their independent probabilities –Ex: Roll of the die two fours 1/6 x 1/6 “AND” The addition rule – probability of any one or two or more mutually exclusive events is calculated by adding the probabilities of these events –Ex: want either a three or a four 1/6 + 1/6 = 2/6 = 1/3 EITHER and OR © 2012 Pearson Education, Inc.

Application of probability to genetics Cross between two pea plants heterozygous for height locus Tt x Tt ½ T and ½ t gametes by each plant –TT ½ x ½ tall –Tt ½ x ½ tall –tT ½ x ½ tall –tt ½ x ½ short © 2012 Pearson Education, Inc.

Solve the problem: What is the probability of rolling two six sided dice and obtaining the following numbers? A) 2 and 3 B) 6 and 6 C) at least one 6 D) Two of the same number ( two 2’s etc) E) An even number on both dice F) An even number on at least one die © 2012 Pearson Education, Inc.

Answers A) 1/18 B) 1/36 C) 11/36 D) 1/6 E) ¼ F) ¾ © 2012 Pearson Education, Inc.

Dihybrid Crosses Crossed peas that differed in two characteristics – two factor cross Generated a unique F2 ratio © 2012 Pearson Education, Inc.

Figure 3.5

© 2012 Pearson Education, Inc. The product law can be used to predict the frequency with which two independent events will occur simultaneously Dihybrid crosses are basically two monohybrid crosses conducted separately.

© 2012 Pearson Education, Inc. Figure 3.6

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Mendel's fourth postulate: Independent assortment –states that: –traits assort independently during gamete formation –all possible combinations of gametes will form with equal frequency –Due to the independent separation of homologous pairs of chromosomes in meiosis

Now Solve This © 2012 Pearson Education, Inc.

Answer © 2012 Pearson Education, Inc.

The Trihybrid Cross Demonstrates That Mendel's Principles Apply to Inheritance of Multiple Traits

© 2012 Pearson Education, Inc. The Trihybrid cross demonstrates that Mendel's principles apply to inheritance of multiple traits Trihybrid crosses involving three independent traits show that Mendel's rules apply to any number of traits

© 2012 Pearson Education, Inc. The forked-line method, or branch diagram The forked-line (branched diagram) method is easier to use than a Punnett square for analysis of inheritance of larger number of traits

© 2012 Pearson Education, Inc. Figure 3.9

© 2012 Pearson Education, Inc. Table 3.1

© 2012 Pearson Education, Inc. Chi-Square Analysis Evaluates the Influence of Chance on Genetic Data

© 2012 Pearson Education, Inc. Chi-Square analysis evaluates the influence of chance on genetic data Chance deviation from an expected outcome is diminished by larger sample size

© 2012 Pearson Education, Inc. Chi-Square Calculations and Null Hypothesis When we assume that data will fit a given ratio, we establish what is called the null hypothesis—so named because it assumes that there is no real difference between the measured values (or ratio) and the predicted values (or ratio) The apparent difference can be attributed purely to chance

© 2012 Pearson Education, Inc. Chi-square (  2 ) analysis is used to test how well the data fit the null hypothesis Table 3.3 shows the steps in  2 calculations for the F 2 generation of a monohybrid cross

© 2012 Pearson Education, Inc. Table 3.3

© 2012 Pearson Education, Inc. Chi-square analysis requires that the degree of freedom (df) be taken into account, since more deviation is expected with a higher degree of freedom (Figure 3.11) The degree of freedom is equal to n – 1, where n is the number of different categories into which each datum point may fall

© 2012 Pearson Education, Inc. Figure 3.11

© 2012 Pearson Education, Inc. Once the number of degrees of freedom is determined, the  2 value can be interpreted in terms of a corresponding probability value (p)

Now Solve This: © 2012 Pearson Education, Inc.

Pedigrees Reveal Patterns of Inheritance of Human Traits

© 2012 Pearson Education, Inc. Pedigrees reveal patterns of inheritance of human traits A pedigree shows a family tree with respect to a given trait. Pedigree analysis reveals patterns of inheritance

© 2012 Pearson Education, Inc. Figure 3.12

© 2012 Pearson Education, Inc. Figure 3.13

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Table 3.4

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