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Human Heredity

Human Heredity. Learning Target 14.1. Explain how human traits are inherited. Explain why human traits are not ideal for the study of genetics. Discuss the influence of the environment on gene expression. Studying Genetics.

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Human Heredity

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  1. Human Heredity

  2. Learning Target 14.1 • Explain how human traits are inherited. • Explain why human traits are not ideal for the study of genetics. • Discuss the influence of the environment on gene expression.

  3. Studying Genetics • 100 years ago Thomas Hunt Morgan proposed using the fruit fly Drysophyla melanogaster as a way of studying genetics for three reasons. 1. They reproduce quickly (2 weeks) 2. They are small and can be kept in large numbers 3. They only have 8 chromosomes (4 pair) which are relatively large and easily seen.

  4. Here is what is done! • The human organism in contrast contains 23 pairs, or 46 chromosomes • To study these biologists must trap cells in the metaphase stage of mitosis using a poison that destroys microtubules. • From here they take a picture, cut out the chromosomes and pair them up in what’s known as a karyotype. • A karyotype reveals there are two sex chromosomes, X and Y and 44 autosomes

  5. Karyotype

  6. Normal female

  7. Normal Male

  8. Reproductive Cells • Human sex cell contains 22 autosomes and 1 sex chromosome • The egg and sperm unite to form a zygote • During meiosis females will produce an egg with an X chromosome and males will produce sperm with an X or Y.

  9. Pedigree Analysis • Human generations consist of about 20 years which makes most experiments impossible to carry out. • A Pedigree analysis makes it possible to study several generations of traits

  10. Pedigree

  11. Genes and People • Many human traits are inherited by the action of dominant and recessive genes, although other traits are determined through more complicated gene interactions

  12. Human Blood Groups • Multiple alleles are three or more alleles of the same gene that code for a single trait. ABO and RH blood groups are determined by multiple alleles.   • In 1900 an Australian physician Karl Landsteiner discovered that there were four types of blood groups

  13. Individuals with AB Blood Produce both antigens Blood type is Individuals with AA or AO Produce only A antigens Blood type is Individuals with BB or BO Produce only B antigens Blood type is Individuals with OO Do not produce antigens blood type is Blood Types

  14. Human Blood Groups • Blood type exists as four possible phenotypes • There are 2 main genes responsible for blood type • ABO Blood Groups – determined by single gene with 3 alleles (MULTIPLE ALLELES) • Rh Blood Groups – determined by single gene with 2 alleles • Rh+ allele is dominant over Rh- allele • What is phenotype of someone who is Rh positive? • What is phenotype of someone who is Rh negative?

  15. ABO Blood Group • The three alleles are: • IA (we will write as A)- Codes for “A” blood • IB (we will write as B)- Codes for “B” blood • i – recessive allele (we will write as O)- Codes for “O” blood

  16. ABO Blood Group • Alleles A and B are codominant • These alleles produce antigens that can be recognized by immune system on the surface of the blood cells • The allele for O is recessive to the alleles A and B • Individuals with ii (or O blood type) produce NO antigens

  17. Universal Recipient and Donor • Universal Donor – Blood Type O • Has NO antigens • Universal Recipient – Blood Type AB • Has BOTH antigens SAFE TRANSFUSION PHENOTYPE GENOTYPE ANTIGEN TO FROM

  18. Referring to a Blood Type • When you refer to a blood group, you use both groups at the same time • EX: Person with AB- Blood Type • Individual has AB alleles from the ABO Gene • Individual has Rh- allele from the Rh gene

  19. Lets try it together: Suppose a mother who is heterozygous for A blood type has a child with a father who is blood type O. What would their potential children's blood types be? When they had they had their first born child there was a bit of a mix up at the hospital and they are not sure that they brought home the right baby. The baby they brought home is homozygous A. Is this their child??

  20. Learning Targets 14.2 • How is sex determined? • How do small changes in DNA cause genetic disorders. • Why are sex-linked disorders more common in males than in females?

  21. Sex Chromosomes • In the early part of the nineteenth century Nettie Stevens discovered the sex chromosomes X and Y when studying the meal worm. • It was later discovered that humans displayed the same system. It is the presence or absence of the Y chromosome that determines the sex of an individual

  22. Sex Chromosomes

  23. In 1909 Thomas Hunt Morgan did an experiment on fruit flies to see how white eyes were inherited. • He did a cross between a white eyed male and a red eyed female and found all were red eyed. Xr Y XRXr XRY XR XR XRY XRXr

  24. When he did the F2 cross he found ¼ white eyed flies like he expected however he noticed all the white eyed flies were male. • Morgan had found Sex-linked (X linked) genes. XR Y XRXR XRY XR Xr XrY XRXr

  25. Sex Linked Genes • Sex Linked Genes — found on sex chromosome • Ex: Colorblindness, Hemophilia, Duchenne Muscular Distrophy • Many sex-linked genes are found on the X chromosome • More than 100 sex-linked genes are on the X chromosome • Y Is much smaller and appears to contain few genes

  26. Sex Linked Genes • Since males have only one X chromosome, all X-linked alleles are expressed • So, sex linked diseases are more common in males • Sex linked genes move from Mothers to Sons • In females, there is an extra X, so one X is randomly switched “off” • The “off” X forms a Barr body – just a dense region of nucleus

  27. Examples of Sex-Linked Disorders • Colorblindness • Three genes associated with color vision are on X • A defective version of any of these produces colorblindness in males • Red-green is the most common form, and appears in 1 in 10 males in the US • In Females, it is rare—1 in 100 females has colorblindness • WHY IS IT DIFFERENT IN MALES & FEMALES? • Colorblindness is recessive • Females must have two copies of allele to have disorder • Males have just one X and only need one copy

  28. Father (normal vision) Colorblindness Normal vision Colorblind Male Female Daughter (normal vision) Son (normal vision) Mother (carrier) Daughter (carrier) Son (colorblind)

  29. Examples of Sex-Linked Disorders Hemophilia • Individuals with the recessive alleles for hemophilia are unable to clot blood properly. • It affects about 1 in 10,000 males and 1 in 1 million females.

  30. Examples of Sex-Linked Disorders Duchenne Muscular Dystrophy • It affects 1 in 3,000 males who suffer a sudden weakness in muscles that eventually leads to death

  31. Autosomal Genetic Disorders • Although many genetic disorders are located on the X chromosome, the majority are located on autosomes. • Autosomal Disorders – found on the autosomes #1-22 • Ex: Albinism, Cystic Fibrosis, Tay Sacks, Sickle Cell Anemia, Huntingtons Disease

  32. Types of Autosomal Disorders • Albinism • Albinism is a condition in which the skin is unable to produce melanin a skin pigment. • Albinism is caused by a recessive allele on chromosome 11.

  33. Types of Autosomal Disorders Cystic fibrosis •  Cystic fibrosis is the most common fatal genetic disease. • It affects people of European ancestry affecting 1 in every 2500 people. • Cystic fibrosis is found on chromosome 7 and causes a build up of liquid in the lungs

  34. Types of Autosomal Disorders Tay-Sacks Disease • Tay-Sacks disease is a fatal genetic disorder caused by a recessive allele. • It affects people of Jewish ancestry. • People affected by Tay-Sacks suffer a rapid breakdown of the nervous system.

  35. Types of Autosomal Disorders • Sickle Cell Anemia • The condition causes many of the blood cells to be sickle shaped. • A person with sickle cell anemia is easily deprived of oxygen and the affected blood cells often become lodged in capillaries which causes serious damage or death.

  36. The gene for sickle cell anemia (S) is codominant with the normal hemoglobin gene (A). • People who are heterozygous are carriers and about half of their blood cells are affected.  • These people suffer few ill effects. S A S S S S A S A A A A

  37. Types of Autosomal Disorders • People who are homozygous SS are sufferers and are severely affected because all their blood cells are sickle shaped. • * People of African ancestry are the most common carriers of sickle cell anemia.

  38. About 10% of people in USA are carriers but as many as 40% are carriers in some African countries. • The reason it is so common even though it is detrimental is that people who are carriers are partially resistant to malaria. •   Those who are normal are not resistant and those who have sickle cell usually don't reproduce. • This causes carriers to be more common in some regions.

  39. Types of Autosomal Disorders Huntington Disease • Huntington disease, which is produced by a single dominant allele (H), is an example of a genetic disease. • Huntington disease is a disease that does not express itself until a person reaches their thirties or forties.

  40. Types of Autosomal Disorders • The disease causes a painful progressive loss of muscle control and mental function until death occurs. • Because the disease doesn't express itself until later in life, it is often passed on to the next generation.

  41. Polygenic traits • Human traits controlled by a number of genes are called polygenic. • Example; height, weight, and skin color

  42. Chromosomal Disorders • NONDISJUNCTION: Homologous chromosomes fail to separate during meiosis (literally means “not coming apart”) • Possible wrong number of chromosomes in gametes • Possibly resulting in the wrong number of chromosomes in offspring Homologous chromosomes fail to separate

  43. Sex Chromosomal Disorders • The two most common nondisjunction disorders include: • Turners Syndrome • Klinefelter Syndrome • In females, Turner’s Syndrome- • Girls who only get one X chromosome • Genotype: XO • Abbreviated 45XO and are sterile

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