Review. 0 Genotype: alleles that are present 0 Phenotype: physical appearance. 0 If Red is dominant to white, what is the phenotype of the above?

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Ira Hamilton
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2 Review 0 Genotype: alleles that are present 0 Phenotype: physical appearance 0 Rr 0 RR 0 rr 0 If Red is dominant to white, what is the phenotype of the above? 2

3 Vocab to Remember! 0 Allele 0 Gene 0 Trait 0 Dominant 0 Recessive 0 Mendel 0 Autosomes 0 Sex Chromosomes 0 And so forth... 3

4 7.1 Autosomes 0 Any chromosome other than the sex chromosomes 0 How many are there in a diploid human cell? 4

5 Recessive Alleles 0 Only seen when there is no dominant allele present 0 Ex: 0 Homozygous recessive 0 Sex linked 5

6 Recessive Disorder 0 Caused by recessive allele 0 Must not have any dominant alleles in order for disorder to show up 0 More common 6

7 Autosomal Recessive 0 On autosomes NOT sex chromosomes 0 Affects both males and females equally 0 Why? 0 Which pairs could be affected on the right? Disorders 7

8 Carriers Heterozygous Have 1 recessive allele Appear normal Show no symptoms Can pass recessive allele on Offspring could have disease 8

9 Which Crosses? 0... Could produce an affected individual? 0 This one? 0 How about this one? 0 And this one???? 9

10 Dominant Disorder 0 Caused by dominant allele 0 Only need one allele for disorder to present 0 Far less common 0 Progeria The Medical Breakthrough 12 min 10

11 Sex Linked Traits 0 Genes are located on sex chromosomes NOT on autosomes 0 X chromosome is larger 0 Holds more info than Y 0 Has more influence on phenotype 0 ~1000 genes on X 0 ~78 on Y 0 Which chromosomes are sex linked? 11

12 Sex-Linked Gene Expression 0 Different than autosomal 0 Whatever is carried on the X chromosome is expressed in males... 0WHY? 0 Males XY 0 Females - XX 12

13 Here Kitty, Kitty... 0 Why are calicos always females? 0 Has to do with the X chromosome... 13

14 X Chromosome Inactivation 0 One X chromosome coils VERY tightly 0 Becomes inactivated 0 Not expressed 0 Causes Calico coloration in cats 0 Alleles expressed randomly across their body 14

15 7.2 Complex Patterns of Heredity Polygenic traits Multiple alleles Incomplete dominance Codominance 15

16 Mendelian Genetics 0 Had only two possible phenotypes 0 Explains some traits 0 BUT not all... 0 Some traits are more complicated 16

17 Incomplete Dominance Intermediate form No dominant No recessive Heterozygous individual is different from either parent Produces a new phenotype 17

18 Incomplete Dominance Ex: Primroses Four-o-clocks Snapdragons Betta fish 18

19 Incomplete Dominance Sometimes written using different letters: Red = RR White = WW Thus: Pink = RW Or using subscripts: R 1 R 1 = Red R 2 R 2 = White R 1 R 2 = Pink 19

20 Incomplete Dominance Why? The single "red" allele is unable to code for the production of enough red pigment to make the petals dark red 20

21 Betta Fish 0 Green = homozygous = B 1 B 1 0 Steel Blue = homozygous = B 2 B 2 0 Royal Blue = heterozygous = B 1 B 2 21

22 Codominance Neither allele is dominant nor recessive Heterozygous display both traits Both alleles are expressed completely but separately Ex: Blood type AB Flower colors (some) 22

23 Multiple Alleles Genes with three or more alleles = Possible alleles But REMEMBER: only inherit two One from each parent Ex: Human blood type 23

24 Blood Type 0More complicated: 0 Multiple alleles 0 Codominance 0 Dominant/recessive 0 Determined by presence of antigens (protein) on blood cells 0 A antigen 0 B antigen 0 O = no antigens 24

25 Blood Type: If a person receives an A allele and a B allele, their blood type is type AB What if they get an A and an A? 25

26 Human Blood Types Controlled by 3 alleles Four possible phenotypes: A, B, AB, and O O is recessive A and B are codominant 26

27 ABO Blood Types 27

28 Human Blood Types 28

29 Polygenic Traits Influenced by several genes May be on same or different chromosome Many combinations occur in offspring Degrees of intermediate conditions 29

30 Polygenic Traits Ex: Eye color Height Weight Hair color Skin color 30

31 Epistasis 0 When a gene interferes with the expression of other genes 0 Ex: 0 Albinism a gene blocks production of pigments 0 Skin, hair, and eyes = light 31

32 Traits and the Environment Phenotype often depends on the environment Ex: Hydrangea flowers In acidic soil bloom blue In basic soil bloom pink 32

33 Traits and the Environment Ex: Arctic fox Temperature affects pigment production gene In summer pigment made In winter-no pigment made 33

34 Traits and the Environment Ex: Siamese cats Temperature affects fur color Cooler regions of body = darker fur 34

35 Traits and the Environment 0 Ex: Turtles 0 Sex determined by temperature 0 Warm temperature = females 0 Cooler temperature = males 35

36 7.3 Gene Linkage 0 Genes that tend to be inherited together = linked 0 First described by 0 William Bateson and R.C. Punnett (also invented Punnett Square) 0 Studied dihybrid crosses in peas 36

37 Thomas Hunt Morgan Studied fruit flies = Drosophila melanogaster Determined chromosomes made up of genes Sex-linked traits were discovered 37

38 Linkage Maps 0 Show relative location between linked genes 0 First made by Alfred Sturtevant, a student of Morgan s 0 Used crossing over frequencies 38

39 7.4 Pedigree Shows how a trait is inherited over several generations A chart Symbols represent people Lines represent relationships Allows us to see disorder quickly 39

40 Pedigree Basics: 40

41 Autosomal Recessive Trait Allele located on autosome Affects both males and females Recessive = only shows up if homozygous recessive! 41

42 Autosomal Dominant Trait Allele located on autosome Affects both males and females Dominant = if present allele it is expressed! 42

43 Sex-linked Traits-Recessive Allele located on sex chromosome On X chromosome Affects mostly males 43

44 Determine the Type of Trait Autosomal or sex-linked? Dominant or recessive? How can we tell? 44

45 Albinism Determine the genotypes of individuals: 45

46 Genetic Disorders Harmful effects produced by inherited mutations Many carried by recessive alleles Carriers Heterozygous (Ex: Tt) Appear normal Carry a recessive gene Can pass it on 46

47 Human Genetic Disorders Ex: Sickle Cell Anemia Recessive Affects blood Produces defective hemoglobin Carries oxygen Found in RBC 47

48 Sickle Cell Anemia Causes many RBCs to bend Become sickleshaped Cells rupture easily and get stuck in vessels Blocks blood flow Not enough oxygen 48

49 Sickle Cell Anemia Interesting fact: If Heterozygous: Protected from malaria! Sickled cells kill protist that causes malaria Still have enough normal cells to carry oxygen 49

50 Human Genetic Disorders Ex: Cystic Fibrosis Recessive Most common in Caucasians 1 in 25 Caucasians = carriers 1 in 2,500 Caucasian infants = homozygous recessive = disorder 50

51 Cystic Fibrosis Produces abnormally thick mucus Affects lungs Blocks ducts of liver and pancreas Treatment only relieves symptoms No known cure 51

52 Human Genetic Disorders Ex: Hemophilia Hemo = blood Philia = tendency toward Tendency to bleed excessively 52

53 Hemophilia Sex linked Recessive Many genes code for proteins involved in blood clotting one is on X chromosome 53

54 Hemophilia Blood does not clot properly Extended bleeding time Minor cuts and bruises treated the same Internal bleeding in joints = problem Leads to arthritis and limited motion 54

55 Hemophilia No cure Avoid serious injuries May need: Transfusions Injections of blood clotting factors 55

56 Hemophilia Before modern treatments hemophiliacs often died young Fairly normal lives today 56

57 Hemophilia Once called the Royal Disease Trait was found in many Europeans families 57

58 Human Genetic Disorders Ex: Huntington s Disease (HD) Autosomal Caused by dominant allele If inherited it is expressed! Fatal No cure 58

59 Huntington s Disease Symptoms often appear at ages Forgetfulness and irritability Loss of muscle control Severe mental illness Eventually death 59

60 Huntington s Disease Nancy Wexler Studied in Venezuela Located gene in 1993 Now you can be tested 1 in 30,000 in US affected 60

61 Treating Genetic Disorders Most cannot be cured Some can be treated Key: early diagnosis Ex: Phenylketonuria (PKU) Lack enzyme Cannot change phenylalanine to tyrosine Phenylalanine builds up Causes severe retardation Diagnosed and placed on low phenylalanine diet 61

62 Gene Therapy Hope TO: correct certain genetic disorders Replace the defective gene Insert copies of healthy genes 62

63 Genetic Counseling Medical guidance Information about possible genetic problems 63

Punnett Square with Heterozygous Cross (Video clip) There is a glaring error with this video clip. Can you spot it???

Punnett Square with Heterozygous Cross (Video clip) There is a glaring error with this video clip. Can you spot it??? Section 3: Studying Heredity Objectives Predict the results of monohybrid genetic crosses by using Punnett squares. Apply a test cross to determine the genotype of an organism with a dominant phenotype.