Pedigree Analysis: Types of Inheritance, Mendelian Principles, and Pedigree Charts - PDF

Sex limited traits Only in one sex. 1.Lactation (milk production for female) 2.Beards/ moustache 3.Egg laying in female eggs. 4.Pre- eclampsia in female (increased blood pressure during pregnancy)  Sex- influenced traits Baldness BB – male bald, female bald bb – non bald, non bald Bb- Bald,...

Sex limited traits Only in one sex. 1.Lactation (milk production for female) 2.Beards/ moustache 3.Egg laying in female eggs. 4.Pre- eclampsia in female (increased blood pressure during pregnancy)  Sex- influenced traits Baldness BB – male bald, female bald bb – non bald, non bald Bb- Bald, non bald  Sex-linked inheritance Hemophilia Normal female – XHXH Carrier female – XHXh Hemophiliac female – XhXh Normal Male- XHY Hemophiliac Male- XhY Color blindness  Extension and Modification of Mendelian Principle Mendelian Analysis !Mendel followed single genes through multiple generations – Law of Segregation – Law of Independent Assortment !Observed ratios of !3:1 and 1:2:1 in monohybrid crosses and !9:3:3:1 in dihybrid crosses !These ratios explain some inheritance Mendelian Analysis in Humans " Most traits are affected by more than one gene " cannot be analyzed using simple Mendelian genetics. " Some are relatively simple genetically " follow the pattern of Mendelian inheritance. " Many single gene traits that can be Genetics is not straightforward in humans: " no true-breeding humans " generation time is long (impractical) " controlled matings??? " siblings rarely mate to Pedigre  Pedigr ee A pedigree is a drawing of a family tree.  The pedigree is used by genetic counselors and other medical professionals to assess families and try to spot patterns or indications which may be helpful in  Creating Your Pedigree: 3 Steps Step 1: Your Family’s Information Write a list of all your family members, including: Parents Brothers and sisters (include half- siblings) Children Grandparents Aunts and uncles Cousins Nieces and nephews Next to each family member’s name, write down everything you know about their health and medical history. If you are adopted, you can collect information on either or both your adopted and birth families.  Information to Include Age or date of birth (or best guess, e.g. 40’s) Date of death for family members who have passed away Height and weight (optional) For those with medical problems, write down things like if they smoked, diet or exercise habits, etc. For those with medical conditions, write down how old the person was when they  Medical conditions such as: Cancer Learning problems or Heart disease mental retardation Diabetes Vision or hearing loss at a Asthma young age Mental illness Known genetic conditions, High blood pressure like cystic fibrosis or Stroke sickle cell disease Kidney disease Birth defects (e.g. spina bifida, cleft lip, heart  Step 2: Drawing Your Family Tree Symbols Used in Drawing  Ready to Draw! First, start with yourself! Place yourself towards the bottom or middle of the center of the page, because older generations will go above you But leave space underneath your symbol for your information; Date of birth, any medical conditions, height and An arrow next to you represents that YOU are the person who called attention to this family  Siblings Draw your brothers and sisters next to yourself Older siblings go on your left, younger siblings on your right Then draw vertical lines up from each sibling and connect the vertical lines with a horizontal line. This represents  Parents Draw your parents above yourself Draw a horizontal line connecting your parents. Then draw a vertical line from the horizontal line to your symbol (if only child) or the sibshipline. The horizontal line is a relationship line. If your biological parents are divorced or not together, draw a diagonal line through the horizontal line. If either of your parents have children with a different partner, draw a second relationship line to the other partner. Any half-siblings from this relationship should have a vertical line  Aunts, Uncles, Cousins, Nieces & Nephews Your parents’ siblings (your aunts and uncles) are drawn next to them and connected with a sibshipline. It’s okay if you have to draw them out of order by age, but do your best! In order to save space, you may choose not to include the spouses of your parents’ brothers and sisters. When drawing cousins, connect their line of descent directly to their parent or to their parents’ relationship line. Same concept when drawing the children  Grandparents Draw your maternal grandparents above your mother, or your mother’s sibshipline. Connect them with a relationship line (if applicable) and draw a line of descent to your mother or Draw your paternal grandparents above your father, or your father’s sibshipline. Connect them with a relationship line (if applicable) anddraw a line of descent to your father or Step 3: Put it all together and what do you get... 1. Why would a pedigree be useful to a doctor or genetic counselor? 2. What can be determined from looking at our example pedigree? If you were a doctor or genetic counselor, what would you discuss with our example family? 3. Should all doctors be required to ask their patients about their family health Pedigree Analysis  In humans we must use pedigrees to study inheritance Pedigrees are an orderly diagram of a families relevant genetic features extending through multiple generations Pedigrees help us infer if a trait is from a single gene and if the trait is  STEPS WHEN INTERPRETING A PEDIGREE CHART 1.Determine what type of disorder the pedigree chart shows. 2.Determine whether the disorder is dominant or recessive.  Types of Disorder  Autosomal  X-Linked  Y-Linked  Mitochondrial  Chromosomal 1. autosomal- If it is a 50/50 ratio between men and women the disorder. Two types (Autosomal dominant and Autosomal Recessive) 2. X-linked- If most of the males or females in the pedigree are affected, then the disorder. Two types (X-linked Dominant and X-linked Recessive) 3. Y-Linked - If it is only males that are affected the disorder 4.Mitochondrial - If the trait is inherited from mother only the disorder. After determining the type of disorder follow the next step.  STEPS WHEN INTERPRETING A PEDIGREE CHART 1.Determine what type of disorder the pedigree chart shows. 2.Determine whether the disorder is dominant or recessive.  If the disorder is dominant, one of the parents must have the disorder.  If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.  Rules of Inheritance  Autosomal Dominant Appears in both sexes with equal frequency Both sexes transmit the trait to their offspring Does not skip generations  Affected offspring must have an affected parent unless they posses a new mutation When one parent is affected (het.) and the other parent is unaffected, approx. 1/2 of the offspring will be affected Unaffected parents do not transmit the trait  BRACHYDACTY LY is a shortening of the fingers and toes due to unusually short bones. This is an inherited condition, and in most cases does not present any problems for the  Autosomal Recessive Appears in both sexes with equal frequency Trait tend to skip generations Affected offspring are usually born to unaffected parents  When both parents are hetrozygous, approx. 1/4 of the progeny will be affected Appears more frequently among the children of consanguine marriages  X-Linked Dominant Both males and females are affected; often more females than males are affected. Does not skip generations. Affected sons must have an affected mother; affected daughters must have either an affected mother or an affected father.  Affected fathers will pass the trait on to all their daughters. Affected mothers if heterozygous will pass the trait on to 1/2 of their sons and 1/2 of their daughters.  X-Linked Recessive More males than females are affected Affected sons are usually born to unaffected mothers, thus the trait skips generations Approximately 1/2 of carrier mothers’ sons are affected It is never passed from father to son All daughters of affected fathers are carriers  Y-Linked Dominant Only males are affected It is passed from father to all sons It does not skip generations  Mitochondrial Trait is inherited from mother only All children of a mother are at risk to be affected or carriers. Representative Recessive and Dominant Traits  Best identified by cytogenetic testing based on clinical findings such as the following: o Combinations of major and/or minor congenital anomalies o Mental retardation with or without major/minor anomalies o Recurrent pregnancy loss o Sexual development disorders (e.g., ambiguous genitalia, primary amenorrhea, delayed puberty) o Infertility Stillbirth or infant death  Try to identify what type of disorder and trait are present in the following: (briefly discuss your answer) 1. 2.  X-Linked Dominant Both males and females are affected; often more females than males are affected Does not skip 3.  Autosomal Recessive When both parents are hetrozygous, approx. 1/4 of the progeny will be affected Appears more frequently among the 4.  Y-Linked Dominant Only males are affected It is passed from father to all sons It does not skip generations 5. Assignment based on we've discussed, create a Pedigree of your family from 1st Generation (Grandparents unto your Generation). Include the disorders or diseases passed from generation to generation even the Acquired diseases. Problem 1: Here are four human pedigrees. The black symbols represent an abnormal phenotype inherited in a simple Mendelian manner. a. For each pedigree, state whether the abnormal condition is dominant or recessive. Try to state the logic behind your answer. b. Problem 2: Consider the accompanying pedigree of a rare autosomal recessive disease, PKU. a. List genotypes of as many of the family members as possible. b. If individuals A and B marry, what is the probability that their first child will have PKU? c. If their first child is normal, what is the probability that Phenylketonuria (commonly known their second child will have as PKU) is an inherited disorder that increases the levels of a substance PKU? called phenylalanine in the blood. d. If their first child has the Phenylalanine is a building block of disease, what is the probability proteins (an amino acid ) that is obtained through the diet. It is found in that their second child will be all proteins and in some artificial https://medlineplus.gov/genetics/condition/phenylketonuria/ #:~:text=Phenylketonuria%20(commonly%20known%20as%20PKU,and%20in