Chapter 14. Human Genetics

Transcription

1 Chapter 14 Human Genetics

2 Human Chromosomes Humans have 46 chromosomes 22 pairs of our chromosomes are autosomes Chromosomes that are not sex chromosomes 1 pair of our chromosomes are sex chromosomes XX = girl XY = boy

3 We can organize all of our 46 chromosomes from largest to smallest into a chart called a karyotype The sex chromosomes are always listed at the end

4 Karyotypes are useful tools for diagnosing patients with chromosomal genetic disorders Down Syndrome, Fragile X syndrome, Turners, etc

5 Amniocentesis How do we get these chromosomes? Procedure of removing fetal cells from the amniotic fluid in the womb

6 Pedigrees A pedigree is a tool used to determine the mode of inheritance of a gene in a particular family

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8 Pedigree Activity This is the story of Grandma and Grandpa Flipnob and their clan. They were married way back in 1933, and have been just like newlyweds ever since. From their union, four individuals were created. Elizabeth, the eldest, was born in Fred soon followed in In 1939 Michelle was brought into this world. Mickey (a surprise to the whole family) was the baby of the family, not being born until 1950.

9 Elizabeth fell in love at a young age, and wed her high school sweetheart, David in From this marriage, two bundles of joy came about (at the same time) Identical Twins!! John and Sonny

10 It took Fred a little longer to find his soul mate. Finally in 1970, Fred found the woman of his dreams, Wilma and they were married. Since they married so late in life, they only brought one new person into this world Barney

11 Michelle was a hard working woman, and never found time in her schedule for love. She led a very productive and fulfilling life, but she never did marry and have children.

12 Mickey was a wild one!! After a long string of girlfriends, he finally chose Monica to spend the rest of his life with. They were wed in 1975 and brought two girls into this world. Krista 1977 Janet 1979

13 Questions Not having freckles is a recessive trait. Grandpa Flipnob did not have freckles, but his beautiful bride did. Fred and Michelle were the only two of their siblings to have freckles. Of the grandchildren, the twins did not have freckles, and neither did Barney, but the two girls did

14 Assign two recessive genes to any person on the pedigree whose symbol is shaded. Small letters are written below the person s symbol Assign only one dominant gene to any person on the pedigree whose symbol is unshaded. A capital letter is written above the symbol. Us this information to determine the second alleles for each person with the dominant phenotype.

15 Chromosomal disorders & blood types

16 Blood Group Genes Rh factor is determined by a single gene It is dominant so an individual with Rh+/Rh+ or Rh+/Rh- are said to be Rh positive A person with two Rh- alleles is said to be Rh negative Rh stands for Rhesus monkey

17 The A, B, AB and O blood groups are controlled by multiple alleles I A I A and I A i = blood type A I B I B and I B i = blood type B I A I B = blood type AB ii = blood type O

18 Blood Types - Multiple Alleles and Codominance In humans, there are four blood types (phenotypes): A, B, AB, and O O is recessive, two O alleles must be present for the person to have type O blood A and B are codominant. If a person receives an A allele and a B allele, their blood type is type AB Crosses involving blood type often use an I to denote the alleles - see chart.

19 to know whether at type A or B person is heterozygous or homozygous. Type O's are automatically OO and type AB is automatically AB. Crosses are performed the same as any other.

20 The blood type determines what antibodies are located within the blood. Type A blood has type B antibodies. If type B blood is put into their bodies, their immune system reacts as if it were a foreign invader, the antibodies clump the blood - can cause death. Type AB blood has no antibodies, any blood can be donated to them - they are called the "universal acceptors" Type O blood has no surface markers on it, antibodies in the blood do not react to type O blood, they are called the "universal donors"

21 What happens when you give a person with type A blood, type B blood? Clumping can occur and it is deadly!

22 Human Genes Human genome our complex set of genetic information Human Genome Project An international effort to map all 4 billion base pairs of the human genome. It is complete and the information is being used to help those with genetic disorders

23 Chromosomal Disorders Down Syndrome Occurs from nondisjunction (failure of chromosomes to separate during meiosis) Three copies of chromosome 21 Mild to severe mental retardation, increased susceptibility to many diseases, other birth defects

24 Recessive Alleles Most genetic disorders are recessive This means the child has to inherit both alleles for the trait from the parents Example: Cystic Fibrosis Excess mucus in lungs, digestive tract, liver and increased susceptibility to infections

25 Cystic fibrosis is autosomal recessive C c Recessive and found on an autosome C CC Cc What is the probability of having a child with CF if both parents are heterozygous for the trait? c Cc cc

26 Another Autosomal recessive disorder is PKU (Phenylketonuria) Lack of normal skin pigment; mental retardation It is treatable and we are all tested when we are born

27 A woman who is a Phenylketonuric marries a man who is normal. They have a child that is diagnosed with PKU at birth. What is the father s genotype? P P p Pp Pp p p Pp Pp p Possible genotypes? P Pp Pp PP or Pp p pp pp

28 Dominant Alleles Some genetic disorders are dominant Example: Huntington s Disease Progressive loss of muscle coordination and mental function until death occurs

29 A Man who is heterozygous for Huntington s disease has a child with a woman who does not carry a gene for Huntington s. What is the probability that they will have a child with Huntington s? h h H H h H h h h h h h

30 Codominant Alleles Example: Sickle Cell Anemia People who have sickle cell anemia have abnormally shaped red blood cells This is due to a defect in the hemoglobin protein that carries oxygen These RBC s tend to get stuck in narrow blood vessels which damages cells, tissues and organs

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32 A person who is heterozygous for Sickle cell is said to have Sickle cell trait A mild reversible form of sickling may occur, but may go unnoticed. Heterozygous individuals in tropical regions have an advantage, because this trait renders them resistant to malaria

33 A man and a woman both heterozygous for Sickle cell have a child what are the possible genotypes and phenotypes of this child? A A AA S AS S AS SS

34 Tay-Sachs disease (abbreviated TSD) autosomal recessive a baby with Tay-Sachs disease is born without one of those important enzymes, Hexosaminidase A (Hex A). So, as those fatty proteins build up in the brain, they hurt the baby's sight, hearing, movement, and mental development.

35 Sex linked traits

36 Sex-linked Traits Some genes that code for traits are located on the X chromosome Males are affected more than females because they only have one X chromosome

37 Example: Color blindness Most common form is red-green color blindness If a male has an affected X chromosome, he is color blind, a female with one affected chromosome will be normal, but is called a carrier

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39 A normal male marries a carrier female. What is the probability that they will have a son who is color blind? X X X X Y X Y X c X X c X c Y

40 A colorblind male and a normal female are expecting a child. What is the chance they will have a colorblind boy? X X X c X X c X X c Y X Y X Y

41 Example 2: Hemophilia A blood clotting disorder A cut or bruise could be deadly Proteins called clotting factors now allow hemophiliacs to lead a fairly normal life

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43 A Carrier female and a normal male are expecting their first child. What is the probability that this child will have hemophilia? Carry the gene for hemophilia? X X h X XX XX h Y XY X h Y

44 Sex Chromosome disorders Too many or not enough sex chromosomes Example: Females can have Turner syndrome (45X) Most look normal, may have decrease life span and are usually sterile Male s can have Klinefelter Syndrome (47XXY) Most look normal, but may be infertile. They may exhibit some emotional or social problems

45 Human DNA Analysis We can test for the presence of certain alleles by using gene probes Fluorescent tags that attach to the gene of interest

46 DNA fingerprinting Using gel electrophoresis, scientists can identify individuals based on their DNA code Everybody has a unique DNA fingerprint Paternity cases, Crime investigations

47 Gene Therapy An absent or faulty gene is replaced by a normal, working gene Sometimes viruses are used to carry the gene into the cells. They are modified so they don t cause disease Blood disorders may be treated by bone marrow transplant with normal cells