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Human Inheritance Notes Ch. 14 - Part II Sex-Linked and Autosomal Genetic Disorders.

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Presentation on theme: "Human Inheritance Notes Ch. 14 - Part II Sex-Linked and Autosomal Genetic Disorders."— Presentation transcript:

1 Human Inheritance Notes Ch. 14 - Part II Sex-Linked and Autosomal Genetic Disorders

2 Karyotype Chart Once the cells have been gathered, scientists will take a picture of the chromosomes and make a karyotype chart. Once the cells have been gathered, scientists will take a picture of the chromosomes and make a karyotype chart. Karyotypes show the 23 homologous pairs for the person in which the cells were taken. The pairs are put in order from longest to shortest and numbered from 1 to 23. Pairs 1-22 are called autosomes. Pair 23 are the sex chromosomes. Karyotype interactive

3 Is this a Male or Female Karyotype chart? Female- XX

4 Down Syndrome Chromosome number disorders link Chromosome number disorders link Chromosome number disorders Chromosome number disorders Cells contain one extra copy of chromosome # 21. This results in: characteristic facial features short stature mental retardation shorter life-span Increased risk for heart problems, immune system problems, and cancer. Down Syndrome link

5 Klinefelter Syndrome This results in a male who has This results in a male who has one extra X chromosome. one extra X chromosome.47,XXY This results in This results in This male can not have children. This male can not have children. He can show mental retardation. He can show mental retardation. Is a true male, but can have some female characteristics. Is a true male, but can have some female characteristics. Klinefelter Syndrome Link

6 Sex-linked Inheritance (carried on the X chromosome) Sex-linked disorders are more commonly seen in males. Sex-linked disorders are more commonly seen in males. Genes carried on the X chromosome are said to be sex-linked traits. Genes carried on the X chromosome are said to be sex-linked traits. A carrier is a person who is heterozygous for a disorder, but does not show the disorder A carrier is a person who is heterozygous for a disorder, but does not show the disorder Carriers of sex-linked traits are female. Carriers of sex-linked traits are female.

7 Sex-linked Disorders (carried on the X chromosome) Example 1 : Hemophilia a recessive allele written as X h a recessive allele written as X h What is hemophilia? “free bleeders” What is hemophilia? “free bleeders” A clotting protein is missing. A clotting protein is missing. Uncontrolled bleeding can occur from wounds and bruises. Uncontrolled bleeding can occur from wounds and bruises. Affects 1 out of every 10,000 males Affects 1 out of every 10,000 males

8 PhenotypeGenotype Normal FemaleXHXHXHXH Carrier FemaleXHXhXHXh Female with Hemophilia XhXhXhXh Normal MaleXHYXHY Male with HemophiliaXhYXhY

9 Problem 1: A normal man marries a woman who is a carrier. Create a Punnett square to determine the probability of passing on the allele to their offspring. XhXh XHXH YXHXH XHYXHY XHXhXHXh What are their chances of having a daughter with hemophilia? 0% a daughter who is a carrier? 25% XhYXhY a normal son? 25% a son with hemophilia? 25% XHXHXHXH

10 Sex-linked Disorders (carried on the X chromosome) Example 1 : Colorblindness a recessive allele written as X c a recessive allele written as X c What is the most common form of colorblindness? What is the most common form of colorblindness? Condition where the person cannot distinguish between the colors red and green. Condition where the person cannot distinguish between the colors red and green. Affects 1 out of every 10 males and 1 and 100 females. Affects 1 out of every 10 males and 1 and 100 females.

11 Problem 1: A color-blind man marries a woman who is a carrier. Create a Punnett square to determine the probability of passing on the allele to their offspring. XcXc X C+ YXcXc X C+ YX C+ X c XcXcXcXc What are their chances of having a daughter with normal vision 25% a daughter who is a carrier? 25% XcYXcY a normal son? 25% a color-blind son? 25%

12 Is a sex-linked trait more often seen in males or females? Why? Is a sex-linked trait more often seen in males or females? Why? Sex-linked traits are seen more often in males because males only have to inherit one copy of the trait on the X chromosome he received from his mom! Sex-linked traits are seen more often in males because males only have to inherit one copy of the trait on the X chromosome he received from his mom! How can we tell if a genetic disorder is sex-linked?

13 Sex-linked Disorders (carried on the X chromosome) Example 3 : Duchenne Muscular Dystrophy a recessive allele written as X d a recessive allele written as X d What is muscular dystrophy? What is muscular dystrophy? A disorder that causes the muscles to slowly weaken and eventually leads to death. A disorder that causes the muscles to slowly weaken and eventually leads to death. Affects 1 out of every 3,000 males Affects 1 out of every 3,000 males

14 Autosomal Disorders These are disorders carried on the autosomes, rather than the sex- chromosomes. Most genetic disorders are recessive. Most genetic disorders are recessive. Recessive disordered alleles produce proteins that either malfunction or no longer function. Recessive disordered alleles produce proteins that either malfunction or no longer function. A heterozygous carrier has a normal phenotype because the one “normal” allele produces enough of the required protein. A heterozygous carrier has a normal phenotype because the one “normal” allele produces enough of the required protein.

15 Recessive Autosomal Disorders Albinism Caused by a recessive allele on the chromosome 11. Caused by a recessive allele on the chromosome 11. Individuals who are homozygous recessive are unable to produce melanin, the pigment responsible for human skin color. Individuals who are homozygous recessive are unable to produce melanin, the pigment responsible for human skin color. They have no pigment in their hair or skin, and are sensitive to light. They have no pigment in their hair or skin, and are sensitive to light.

16 Recessive Autosomal Disorders Cystic Fibrosis Caused by a recessive allele on chromosome 7. Caused by a recessive allele on chromosome 7. Found in 1 in every 2,500 Caucasian births. 1 in 25 are carriers. Found in 1 in every 2,500 Caucasian births. 1 in 25 are carriers. Individuals who are homozygous recessive make a defective cell membrane protein. Individuals who are homozygous recessive make a defective cell membrane protein. This creates extra mucus that clogs the lungs and breathing passageways leads to bacterial infections. This creates extra mucus that clogs the lungs and breathing passageways leads to bacterial infections. Two carriers have a 25% chance of having a child with cystic fibrosis.

17 Dominant Autosomal Disorders Dominant disorders are typically lethal and are extremely rare. Dominant disorders are typically lethal and are extremely rare. This is because if a person inherits it he or she dies before they can have children. This is because if a person inherits it he or she dies before they can have children. Exceptions: Exceptions:

18 Huntington Disease This caused by a rare dominant allele on chromosome 4. 1/25,000 affected. This caused by a rare dominant allele on chromosome 4. 1/25,000 affected. Symptoms start with a loss of muscle control. Symptoms start with a loss of muscle control. *No symptoms until age 30 to 40. Mortality within 15 years after systems first appear. *No symptoms until age 30 to 40. Mortality within 15 years after systems first appear. The gene for Huntington disease is dominant, so that every child of a person with the disease has a 50% chance of inheriting the gene and having the disease. The gene for Huntington disease is dominant, so that every child of a person with the disease has a 50% chance of inheriting the gene and having the disease. *This is a lethal disorder, homozygous dominant fetus, the baby miscarries. *This is a lethal disorder, homozygous dominant fetus, the baby miscarries.

19 Huntington Disease *This is a lethal disorder, which means if a person is homozygous dominant the baby miscarries. *This is a lethal disorder, which means if a person is homozygous dominant the baby miscarries. *No symptoms until age 30 to 40. *No symptoms until age 30 to 40. *Why could not showing the disease until later in life be a problem? A person who doesn’t know they have the disorder can pass it on to their children before they show the disease. *Why could not showing the disease until later in life be a problem? A person who doesn’t know they have the disorder can pass it on to their children before they show the disease.

20 Sickle Cell Anemia (codominant disorder) It is found in 1 out of every 1,600 African Americans. (codominant disorder) It is found in 1 out of every 1,600 African Americans. It is an anemia due to the sickled allele producing an alternate from of hemoglobin (red blood protein), which causes cells to sickle or become crescent shaped. It is an anemia due to the sickled allele producing an alternate from of hemoglobin (red blood protein), which causes cells to sickle or become crescent shaped. Individuals with two sickle cell alleles are said to have sickle cell anemia. Individuals with two sickle cell alleles are said to have sickle cell anemia. It can lead to serious medical problems with sickled cells forming blood clots. It can lead to serious medical problems with sickled cells forming blood clots.

21 Pedigree Charts The family tree of genetics What is a pedigree? What is a pedigree? Constructing a pedigree Constructing a pedigree Interpreting a pedigree Interpreting a pedigree

22 What is a Pedigree Chart? A Pedigree chart traces the inheritance of a particular trait through several generations. A Pedigree chart traces the inheritance of a particular trait through several generations. One GOAL of using a pedigree chart is to figure out who are carriers of the trait, because this information is typically unknown. One GOAL of using a pedigree chart is to figure out who are carriers of the trait, because this information is typically unknown.

23 Constructing a Pedigree Male Male Female Female

24 Married Couple- Married Couple- Horizontal Line Horizontal Line Siblings Siblings Vertical line Vertical line More than one Sibling: More than one Sibling: a horizontal line is drawn with a vertical line coming down for each sibling. a horizontal line is drawn with a vertical line coming down for each sibling. Constructing a Pedigree

25 Fraternal twins- Fraternal twins- Two line branching from the same point Two line branching from the same point two eggs and two sperm cells. two eggs and two sperm cells. Identical twins- Identical twins- Also called Maternal Twins Also called Maternal Twins Same as fraternal twins but a horizontal line is added. Same as fraternal twins but a horizontal line is added. one egg and one sperm unite and later splits to form two babies one egg and one sperm unite and later splits to form two babies Constructing a Pedigree

26 I II III Constructing a Pedigree Roman numerals to the left of the pedigree show the generations. Birth Order: children are listed in birth order with oldest on left and youngest on the right.

27 Two horizontal lines from the same person represent two marriages / matings. Example: This man first had a girl with the lady on the left, then had a boy and girl with the lady on the right. Constructing a Pedigree

28 More Symbols in a Pedigree Chart Full Shaded: Full Shaded: Affected person who shows a disorder Affected person who shows a disorder Half shaded: Half shaded: Autosomal carrier Autosomal carrier Circle with dot: Circle with dot: X-linked carrier –always female X-linked carrier –always female Deceased Deceased

29 Pedigrees are used to find out: Pedigrees are used to find out: who are carriers of the disorder & who are carriers of the disorder & the probability of having a future child with the disorder. the probability of having a future child with the disorder. To begin to interpret a pedigree, first determine if the disorder is: To begin to interpret a pedigree, first determine if the disorder is: Autosomal dominant Autosomal dominant Autosomal recessive Autosomal recessive Sex-linked (carried on the X chromosome) Sex-linked (carried on the X chromosome) Predicting using Pedigree Charts

30 Interpreting a Pedigree Chart First ask: Is it a Sex-linked or Autosomal Disorder? If there is a much larger number of males than females who are affected then the disorder is Sex-linked. If there is a much larger number of males than females who are affected then the disorder is Sex-linked. If there is a 50/50 ratio between males and females who are affected then the disorder is autosomal. If there is a 50/50 ratio between males and females who are affected then the disorder is autosomal.

31 Interpreting a Pedigree Chart If it is autosomal disorder then ask: Is it dominant or recessive? If two parents do not show the trait and their children do show it, then it is an autosomal recessive disorder If two parents do not show the trait and their children do show it, then it is an autosomal recessive disorder (parents are heterozygous) (parents are heterozygous) If the disorder is autosomal dominant, then at least one of the parents must show the disorder. If the disorder is autosomal dominant, then at least one of the parents must show the disorder.

32 Practice Examples Does this pedigree show a Does this pedigree show a Sex-linked or Autosomal disorder?

33 Answer: Sex-Linked Disorder much larger number of males are affected

34 Practice Examples Does this pedigree show a Does this pedigree show a Sex-linked or Autosomal disorder?

35 Answer: Autosomal Disorder 50/50 ratio between males and females


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