Genetic Disorders. And Sex- linked Traits

Transcription

1 Genetic Disorders And Sex- linked Traits

2 Chromosomal Abnormalities Aneuploidy: having an extra or missing chromosome fairly common in gametes. Errors in meiosis causes chromosomes to not separate equally into the gametes.

3 Aneuploidy Frequency of Aneuploidy: In males: constant, 1-2% of sperm have an extra or missing chromosome. In females: rate increases with age. Illustrated by the frequency of Down syndrome births at different ages of mother.

4 Aneuploidy Except for the X and Y, humans don t survive with only 1 copy of any chromosome. Also, 3 copies is lethal in most cases. Aneuploidy is a major cause of spontaneous aborkon in early pregnancy. Down Syndrome is the most common human aneuploidy. It is also called trisomy- 21, meaning 3 copies of chromosome number 21.

5 Examples of Aneuploidy 1. Down Syndrome (type of Trisomy) a genekc condikon in which the individual has 3 copies of the 21 st chromosome.

6 Down Syndrome

7 Down Syndrome Phenotype: small broad nose, upward slankng eyes with small folds in corners, some cardiac deformikes, moderate to severe learning disabilikes Occurs about 1 in 1000 births.

8

9 2. Turner Syndrome Missing or incomplete X chromosome (XO)

10 Turner Syndrome Phenotype Develop physically as female Shorter in stature (missing SHOX gene responsible for long bone growth) Ovaries don t develop properly (Sterile, delayed puberty) Stocky build, short webbed neck, low hairline Swelling of hands and feet, heart issues Doesn t affect intelligence Treatment Hormone therapy helps most/all symptoms except the sterility.

11 Turner Syndrome affects 60,000 females in US Seen in 1 of every 2000 to 2500 girls about 800 new cases diagnosed each year.

12 3. Klinefelter Syndrome (XXY)

13 Klinefelter Syndrome XXY The Y chromosome makes physically male Symptoms (subtle and highly varied) Typically testes not fully developed (less testosterone and inferkle) May be taller than average, proporkonally longer arms and legs, less muscle development less body hair, slight breast development, wider hips, sterile, can have some learning disabilikes OZen not diagnosed, or diagnosed accidentally Symptoms helped by testosterone treatment.

14 Klinefelter Syndrome XXY is one of the most common genekc condikons, affeckng about 1 in 660 genekc males.

15 Other Aneuploidy Examples 4. Triplo- X: 5. XYY: 3 X s (female) Male Many undiagnosed Many never because have no diagnosed due to a symptoms. lack of symptoms Some have slight social Tend to be taller, and developmental more physically problems, especially ackve, slight mental language- related. disabilikes, prone to Occasional ferklity acne. problems, but many have normal ferklity.

16 Hermaphrodites?!? Hermaphrodite: An individual that has all female reproduckve parts, and all male reproduckve parts No such thing in Humans

17 XY female (2 ways it can happen) 1. SRY gene inacjvated by mutajon: testes don t develop and the embryo develops as normal female. 2. Androgen insensijvity : person is XY with a funckonal SRY gene, but cells lack testosterone receptor protein, so the cells don t ever get the message that the testosterone is sending. Testes develop in the abdominal cavity, and no ovaries, fallopian tubes, or uterus develop. At puberty, the internal testes secrete testosterone, which gets converted into estrogen and the body develops as a normal (but sterile) adult female.

18 XY women show some male- like features that make them good models Phenotype: Look like women Do not have uterus, don t have periods Some have testes instead of ovaries Taller than most women Chiseled Jaw Good Muscle definikon Don t have as much body fat

19 Hermaphrodites In some cases, androgen insensikvity is only parkal: the cells respond a liale bit to testosterone produced by the testes. The embryo develops with ambiguous genitalia, neither completely male not completely female. Another condikon, congenital adrenal dysplasia, causes the adrenal glands to produce an abnormally large amount of testosterone in a female embryo, This can also cause development of ambiguous genitalia. Another rare condikon: a chimera occurs when two separate embryos fuse together. This can result in a person with some XX cells and some XY cells. This condikon is extremely rare:

20 Chromosome Structure Abnormalities DuplicaJon: an extra copy of a region of chromosome DeleJon:missing a region of chromosome Inversion: part of the chromosome is inserted backwards TranslocaJon: two different chromosomes switch pieces

21 Chromosomal Deletion Cri- du- Chat Syndrome cry of the cat Caused by delejon on the short arm of Chromosome 5 MulKple genes missing

22 Cri- du- chat syndrome Symptoms: Small at birth, larynx doesn t develop correctly (cat- like cry), small head Can have heart defects, problems with hearing and seeing, poor muscle tone Possible HyperacKvity or aggression and severe intellectual disability

23 Causes of Chromosomal Abnormalities DeleKons during the formakon of an egg or sperm, are caused by unequal recombinakon during meiosis. RecombinaKon normally occurs between pairs of chromosomes while they are lined up at the metaphase plate. If the pairs of chromosomes don't line up correctly, or if the chromosome breaks aren't repaired properly, the chromosomes can gain or lose pieces.

24 Twins 2% of births MonozygoJc (IdenJcal) 30% of twins A single zygote splits into 2 between 1 to 9 days azer the zygote forms. The twins share the same genome

25 Dizygotic (Fraternal) 70% of twins Two separate eggs are ferklized with two separate sperm. Two totally independent zygotes are created. The twins have different genomes

26 Conjoined twins very rare (1 in 200,000) IdenKcal twins who fail to completely separate azer the 13 th day azer ferklizakon. May be due to the fusion, or incomplete separakon of zygotes. May be two fully formed individuals connected at various locakons, or rarely, parasikc twins, where one is much smaller and less formed, or even completely contained.

27 Sex Linked Traits Traits that occur on the X or Y chromosome X- linked traits are traits found on the X Chromosome

28 Since males only have one X, all genes on it, whether dominant or recessive, are expressed. A mutant gene on an X chromosome in a female is usually covered up by the normal allele on the other X. Most mutakons are recessive. So, most people with sex- linked genejc condijons are male.

29 Why can females have 2 copies of the X chromosome, when an extra copy of most chromosomes is deadly (like having 3 of any other chromosome? In each cell one of the X chromosomes turns off. This turned off chromosome is known as a Barr body. The effect of Barr bodies can be seen in Calico colored cats.

30

31

32 Example: Calico Colored cats. A calico cat has patches of orange and patches of black X O = orange X B = black Males: X O Y = orange / X B Y = black Females: X O X O = orange / X B X B = black / X B X O = calico Because individual cells determine which X chromosome to deackvate, the patches of color arise

33 Colorblindness We have 3 color receptors in the reknas of our eyes. They respond best to red, green, and blue light. Each receptor is made by a gene. The blue receptor is on an autosome (chrom 7), while the red and green receptors are on the X chromosome (sex- linked).

34 Colorblindness Most colorblind people are males, who have mutated, inackve versions of either the red or the green (somekmes both) color receptors. Most females with a mutant receptor gene are heterozygous: the normal version of the receptor genes gives them normal color vision.

35 How to write a Alleles for Sex Linked Traits Women: Normal: X B X B Carrier: X B X b Colorblind: X b X b Men: Normal: X B Y Colorblind: X b Y

36 Colorblind Test! You will be given a colorblind test. You will see circles with many colors of dots The dot paaern makes up a number What number do you see?

37 With Color Vision:

38 Color Blind Test What number do you see?

39

40 Color Blind Test What number do you see?

41 This what you would see if you were totally color blind What number do you see?

42 Color Blind Test What number do you see?

43 Color Blind Test What number do you see?

44

45

46

47

48

49

50 Color Blind Test What number do you see?

51 Color Blind Test What number do you see?

52

53 Everyone should see this one: Circle, Star, Square

54 Yellow Square (Red/Green CB and Normal) Brown circle (only Normal Vision people)

55 Yellow circle (Red/Green CB and Normal) Brown Square (only Normal Vision people)

56 Which do you see? Normal Vision should see Boat

57 With color vision you see this: But if you were red-green colorblind. You would see the #: 5

58

59 What word do you see?

60 Says No

61 Blue Color Blind

62

63 If you can't make out the '6', '0' or '4' in the 3 circles of this Ishihara color chart respectively, chances are, you have protanopia, deuteranopia, or tritanopia.

64 NO Red is mixed up with blue or green NO Blue or Yellow

65

66 What do the colorblind see? Types of Colorblindness NORMAL PROTAN: Red Blind DEUTERAN: Green Blind TRITAN: Blue Blind RED YELLOW GREEN CYAN BLUE MAGENTA

67 Types of Colorblindness Normal No color vision Protanopia: no red Deuteranopia: no green Tritanopia: no blue

68 Practice Problem 1. A colorblind man marries a female who is a carrier for colorblindness. What is the probability that they will have a child who is colorblind? 2. A male who can see in color marries a female who is a carrier for colorblindness. What are the possible phenotypes of their children?

69 Hemophilia blood does not clot when exposed to air can easily bleed to death from very minor wounds. treated by injeckng the proper clonng proteins, isolated from the blood of normal people. (Now 75% use genekc engineering) 1 in 10, 000 males 1 in 100,000,000 females

70

71 Common amongst royalty in Europe Queen Victoria = Carrier

72

73

74 Practice Problems 3. A woman with hemophilia marries a man who does not have hemophilia. What are the possible phenotypes of their children? 4. A woman without hemophilia marries a man with hemophilia. They have a son with hemophilia. Create a punnea square for this family. What are the probabilikes of their offspring?