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 3.a.3 – The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring (14.1-14.4).

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Presentation on theme: " 3.a.3 – The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring (14.1-14.4)."— Presentation transcript:

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2  3.a.3 – The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring ( ).  4.c.2 – Environmental factors influence the expression of the genotype in an organism – (14.3).  4.c.4 – The diversity of species within an ecosystem may influence the stability of the ecosystem (14.3).

3 Blending Theory 1. Blending Theory - traits were like paints and mixed evenly from both parents Incubation Theory 2. Incubation Theory - only one parent controlled the traits of the children Ex: Spermists and Ovists Particulate Model their 3. Particulate Model - parents pass on traits as discrete units that retain their identities in the offspring

4  Father of Modern Genetics  Mendel’s paper published in 1866, but was not recognized by science until the early 1900’s  Died prior to his “fame”

5 experimental  Used an experimental approach (scientific method) mathematics  Applied mathematics to the study of natural phenomena  Ratios and probability good records  Kept good records and observations  Large test  Large test sample/size

6 1. Short life span 2. Bisexual *Both sexes in one flower/plant *Stamens and carpels 3. Many traits known *Easy to see/observe traits 4. Cross- and self-pollinating *Easy to control reproduction 5. You can eat the failures

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8 two different parents  Cross between two different parents  Results in hybrid offspring ◦ The offspring may be different than the parents.

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10  Cross with only one flower ◦ Stamens/carpels fertilize each other!  Naturally occurring event in pea plants  Results in pure-bred offspring where the offspring are identical to the parents  Is this asexual reproduction???  NO…you still have gametes

11  Used seven characters, each with two expressions or traits  Example  Example: ◦ Character - height ◦ Traits - tall or short

12  Mono = one single character  Crosses that work with a single character at a time ◦ Example - Tall X short

13 Parental  The Parental generation or the first two individuals used in a cross ◦ Example - Tall X short  Mendel used reciprocal crosses, where the parents alternated for the trait

14  F1 - first filial generation ◦ Filial – Latin for “son”  F2 - second filial generation, ◦ Bred by crossing two F1 plants together or allowing a F1 to self-pollinate

15 Notice Notice: only ONE plant shown (self-fertilz.) Notice Notice: TWO P1 plants shown (cross fertilz.)

16 P1 P1 Tall X short (TT x tt) F1 F1 all Tall (Tt) F2 F2 3 tall to 1 short (1 TT: 2 Tt: 1 tt) TallShort

17  Mendel observed SAME pattern in ALL 7 characters ◦ F1 generation showed only one of the traits (regardless of sex) ◦ The other trait reappeared in the F2 at ~25%  3:1 ratio; 3 dominant – 1 recessive  Remember: the % are estimates (still have mutations that could change %)

18 1. Genes can have alternate versions called alleles 2. Each offspring inherits two alleles, one from each parent  He made this conclusion without having knowledge of chromosomes/DNA makeup

19 ** Remember: Each diploid cell has a pair of homologous chromosomes -Therefore, any gene has 2 loci *one on maternal chromo *one on paternal chromo

20 3. If the two alleles differ, the dominant allele is expressed  The recessive allele remains “hidden” (unseen) unless the dominant allele is absent Mendel’s Law of Dominance  Now called Mendel’s Law of Dominance

21 4. The two alleles for each trait separate during gamete formation (meiosis) Mendel's Law of Segregation  This now called Mendel's Law of Segregation

22 Law of Segregation

23  Phenotype  Phenotype - the physical appearance of the organism  Genotype  Genotype - the genetic makeup of the organism, usually shown in a code ◦ T = tall ◦ t = short

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25  Homozygous  Homozygous - When the two alleles are the same (TT/tt)  Heterozygous  Heterozygous- When the two alleles are different (Tt)  Notice (for single-gene traits  Notice (for single-gene traits: ◦ Three choices for genotypes ◦ Homo Dom (TT), Homo Rec (tt), Hetero (Tt)

26 Cross Genotype Phenotype TT X tt all Tt all Dom Tt X Tt 1TT:2Tt:1tt 3 Dom: 1 Res TT X TT all TT all Dom tt X tt all tt all Res TT X Tt 1TT:1Tt all Dom Tt X tt 1Tt:1tt 1 Dom: 1 Res Notice the 3:1 ratio!!!

27  Cross of a suspected heterozygote with a homozygous recessive ◦ Goal: to determine genotype of unknown  Ex: T? X tt *If TT - all Dominant *If Tt - 1 Dominant: 1 Recessive

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29 two  Cross with two genetic traits ◦ Di = two 4 letters  Need 4 letters (two for each trait) to code for the cross ◦ Ex: TtRr (Mono = Tt OR Rr)  Each Gamete  Each Gamete - Must get 1 letter for each trait ◦ Ex. TR, Tr, etc. (when combine = 4 letters)

30  Critical to calculating the results of higher level crosses heterozygous traits  Look for the number of heterozygous traits

31  The formula 2 n can be used, where “n” = the number of heterozygous traits.  Ex  Ex: TtRr, n=2 (2 heterozygous traits) ◦ 2 2 or 4 different kinds of gametes are possible (TR, tR, Tr, tr)  Ex:  Ex: TtRR, n = ? ◦ 2 1 or 2 different gametes are possible

32 TtRr X TtRr  Each parent can produce 4 types of gametes. (n=2; 2 2 =4) ◦ TR, Tr, tR, tr  Cross is a 4 X 4 = 16 possible offspring

33  9 Tall, Red flowered  3 Tall, white flowered  3 short, Red flowered  1 short, white flowered Or: 9:3:3:1 ratio

34  The inheritance of 1st genetic trait is NOT dependent on the inheritance of the 2 nd trait ◦ Ex: Inheritance of height is independent of the inheritance of flower color  This relates to dihybrid crosses – one character’s inheritance is NOT connected to the inheritance of another!

35  Ratio of Tall to short is 3:1  Ratio of Red to white is 3:1  The cross is really a product of the ratio of each trait multiplied together.  (3:1) X (3:1) = 9:3:3:1 ◦ *Use FOIL method to attain ratio

36  Genetics is a specific application of the rules of probability  Probability  Probability - the chance that an event will occur out of the total number of possible events

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38  The monohybrid “ratios” are actually the “probabilities” of the results of random fertilization Ex: 3:1 75% chance of the dominant 25% chance of the recessive

39  The probability that two alleles will come together at fertilization, is equal to the product of their separate probabilities  Steps to determining probability: ◦ 1) Determine ratios for each character/trait  How? Do “little” Punnett squares for EACH trait ◦ 2) Multiply ratios together

40  The probability of getting a tall offspring is ¾.  The probability of getting a red offspring is ¾. (use same Punnett square as above – only with R/r)  The probability of getting a tall red offspring is ¾ x ¾ = 9/16

41 Product Rule  Use the Product Rule to calculate the results of complex crosses rather than work out the Punnett Squares  Ex: TtrrGG X TtRrgg

42 TtrrGG X TtRrgg “T’s” = Tt X Tt = 3:1 “R’s” = rr X Rr = 1:1 “G’s” = GG x gg = 1:0 Product is: (3:1) X (1:1) X (1:0 ) = 3:3:1:1

43 1. Incomplete Dominance 2. Codominance 3. Multiple Alleles 4. Epistasis 5. Polygenic Inheritance

44  When the F1 hybrids show a phenotype somewhere between the phenotypes of the two parents  Ex. Red X White snapdragons F1 = all pink F2 = 1 red: 2 pink: 1 white  NOT BLENDING!!!!!

45 Not enough red pigment made

46  No hidden recessive  3 phenotypes and 3 genotypes (Hint! – often a “dose” effect) ◦ Red = C R C R ◦ Pink = C R C W ◦ White = C W C W

47 Another example

48  Both alleles are expressed equally in the phenotype  NOT an intermediate (like incomplete dominance  Ex. MN blood group ◦ MM, MN, NN  Ex: Rooster/chicken feathers  Ex: flower petal color

49  No hidden recessive  3 phenotypes and 3 genotypes (but not a “dose” effect)

50  When there are more than 2 alleles for a trait ◦ *Remember: only 2 alleles exist for Mendel’s pea plants  Ex. ABO blood group ◦ I A - A type antigen ◦ I B - B type antigen ◦ i - no antigen

51  Multiple genotypes and phenotypes  Very common event in many traits

52 Phenotypes Genotypes A I A I A or I A i B I B I B or I B i AB I A I B O ii

53  I A and I B are dominant  A and B are CODOMINANT  A and B are the names for two different carbohydrates found on the surface of RBCs ◦ Blood types are actually ways of differentiating the type of antigens on a person's red blood cells

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56  Rh blood factor is a separate factor from the ABO blood group  Rh+ = dominant  Rh- = recessive

57  Wife is type A  Husband is type AB  Child is type O Question - Is this possible? Comment Comment - Wife’s boss is type O…There’s some explaining to be done!

58  Factors that are expressed as continuous variation  Lack clear boundaries between the phenotype classes  Ex: skin color, height

59  Several genes govern the inheritance of the trait  Ex: Skin color is likely controlled by at least 4 genes ◦ Each dominant gives a darker skin

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61  Mendelian ratios fail  Traits tend to "run" in families  Offspring often intermediate between the parental types  Trait shows a “bell-curve” or continuous variation

62  Often done by Pedigree charts  Why? ◦ Can’t do controlled breeding studies in humans ◦ Small number of offspring ◦ Long life span

63 Male Female Person with trait

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65 Dominant Trait Recessive Trait

66  Several thousand known!  Some examples: ◦ Albinism ◦ Sickle Cell Anemia ◦ Tay-Sachs Disease ◦ Cystic Fibrosis ◦ PKU ◦ Galactosemia

67  Most common inherited disease among African-Americans  Single amino acid substitution results in malformed hemoglobin  Reduced O 2 carrying capacity  Codominant inheritance

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69  Only affects Eastern European Jews  Brain cells unable to metabolize type of lipid; accumulation of the lipid causes brain damage  Death in infancy or early childhood

70  Most common lethal genetic disease in the U.S.  Most frequent in Caucasian populations (1/20 a carrier)  Produces defective chloride channels in membranes

71  Usually rare  Skips generations  Occurrence increases with consaguineous matings (people descended from the same ancestor)  Often an enzyme defect  Affects males and females equally

72  Less common then recessives  Affects males and females equally  Ex: ◦ Huntington’s disease ◦ Achondroplasia ◦ Familial Hypercholesterolemia

73  Each affected individual had one affected parent.  Doesn’t skip generations.  Homozygous cases show worse phenotype symptoms.  May have post-maturity onset of symptoms.

74  Blood tests for recessive conditions that can have the phenotypes treated to avoid damage  Genotypes are NOT changed  Ex: PKU ◦ Required by law in all states ◦ Tests 1- 6 conditions ◦ Required of “home” births too

75  Where Genetic and Environment Factors interact to cause the disease  Ex: Heart Disease factors ◦ Genetics ◦ Diet ◦ Exercise ◦ Bacterial infections

76  Recognize Mendel's experiments and their role in the scientific discovery of genetic principles.  Identify Mendel's Laws of Genetics.  Recognize the use and application of probability in genetics.  Recognize the basic Mendelian crosses and genetic terminology.  Recognize various extensions of Mendelian genetics and their effect on inheritance patterns.  Identify human traits that exhibit Mendelian inheritance patterns.  Recognize methods used in genetic screening and counseling.  


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