Human Heredity

There are traits that are controlled by one gene with 2 alleles. Often, one is dominant and the other is recessive Example: widow’s peaks and dimples.

Some traits are controlled by a gene with multiple alleles – 3 or more for a single trait. For example: blood types and skin color in humans.

There are 44 chromosomes that we call autosomal chromosomes. However, there are 2 chromosomes that determine our sex and we call them sex chromosomes. These 46 chromosomes all carrier genes on them that determine our traits.

Out of our 23 pairs of chromosomes, 1 pair is the sex chromosomes (X and Y). Female = XX Male = XY

Question: What is the probability that your parents will have a boy or girl? XY (dad) x XX (mom) X Y X X XXXY XXXY Phenotype: 50% boy 50% girl Genotype: 50% XX 50% XY

Question? If my parents have 5 boys in a row, what is the chance they will have a girl the next time? 50%

Human genes are inherited the same way that Mendel discovered. Some traits are controlled by one gene. Therefore, you can study inheritance of traits through a pedigree. A pedigree is a chart or “family tree” that traits a specific trait.

Genetic counselors analyze these charts to infer about genotypes of family member. Dominant gene: →affected individuals have at least one affected parent →the phenotype generally appears every generation

Recessive gene: →unaffected parents can have affected offspring →affected progeny are both male and female

Sex-linked gene: Some traits are carried on the sex chromosomes. Genes on the X or Y chromosomes are sex-linked genes. These traits are passes on from parent to child. Sex- linked genes can be recessive or dominant. MALES are more likely to have a sex-linked trait because they only have ONE X and Y. The allele is USUALLY on the X chromosome. Ex. colorblindness, hemophilia, hairy ears, muscular dystrophy

Are you colorblind? What numbers do you see?

Carrier – person who has one recessive allele and one dominant allele for a trait or heterozygous for that trait (only women can be carriers). Example Hemophiliac carrier X H X h Colorblind carrier X B X b

Carriers do not show that particular trait phenotypically but have a chance to pass the trait on to their child. Carrier – half colored

Reading a Pedigree Task 2: Take out your pedigree sheet and some paper. Lets do the first one together. Do # 2. Come see me to get your paper starred. Task 1: Genotyping a pedigree chart

Sex linked Punnett Squares: Question: What is the probability that a carrier female and a colorblind male will have a girl who is colorblind (b = colorblind, B = normal)? YXbXb XBXB XbXb XBXbXBXb XbXbXbXb XbYXbY XBYXBY Phenotype: 25% normal boy 25% colorblind boy 25% normal girl 25% colorblind girl

Try this one on your own Question: What is the probability that a homozygous (normal vision) female and a colorblind male will have a girl who is colorblind (b = colorblind, B = normal)?

XBXB XBXB XBXbXBXb XBXbXBXb XBYXBY XBYXBY XbXb Y Phenotype: 50% normal girls 50% normal boys Parents: X B X B x X b Y

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Genetics Disorders and Mutations

Mutations … are changes in the genetic material can be good or bad can be on a single gene or the whole chromosome

Genetic Disorder – abnormal condition that a person inherits through genes or chromosomes. They are caused by mutations or changes in a person’s DNA. Write down 3 disorders that have affected someone you know.

Cystic Fibrosis Genetic disorder where the body produces abnormally thick mucus in the lungs and intestines making respiration and digestion difficult caused by a mutation in a gene. The product of this gene is a chloride ion channel important in creating sweat, digestive juices and mucus. One in four babies are born with cystic fibrosis Most common among Northern European descent

Sickle Cell Anemia Sickle cell is a genetic disorder that affects the blood’s hemoglobin. Hemoglobin is the protein in your blood that carries oxygen. Sickle-cell anemia is caused by a point mutation in protein chain of hemoglobin, replacing the amino acid glutamic acid with the amino acid valine The ‘sickle shape’ of the cell doesn’t allow the red blood cell to carry very much oxygen. Most common among African American descent Famous People with Sickle Cell Disease Miles Davis, jazz musician. Paul Williams, singer (The Temptations) Georgeanna Tillman, singer (The Marvelettes) Tionne "T-Boz" Watkins, singer (TLC)

Hemophilia Hemophilia is a genetic disorder in which a person’s blood clots VERY slowly or not at all. A person with hemophilia can bleed to death from a paper cut or scrape. This is sex-linked disorder on the X chromosome. –Queen Elizabeth suffered from this disorder. This man received a vaccine. This is what having hemophilia did to is body.

Down Syndrome Down Syndrome is a genetic disorder that occurs when an individual receives an extra copy of a chromosome. A mistake occurs during Meiosis I: the chromosomes failed to separate correctly (non-disjunction) therefore leaving an extra copy of chromosome #21.

Doctor’s use tools like amniocentesis and karyotypes to help detect most diseases.

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What is a karyotype? Picture of your chromosomes Arranged from largest to smallest quickly identify chromosomal changes

Diagnosis the karyotypes in the back of the room at your table. Make sure to include: Case number Boy or girl Number of chromosomes Normal or abnormal (if abnormal, what is the problem?)

4 Types of Genetic Disorders 1. Single gene –Change in the DNA sequence –More than 6000 known disorders –Autosomal or sex linked –1 in 200 births Examples: cystic fibrosis, sickle cell anemia, Marfan syndrome, Huntington’s disease

Types of Genetic Disorders 2. Multi-factoral –combination of environmental factors and mutations in multiple genes –more complicated Examples: heart disease, high blood pressure, Alzheimer’s disease, arthritis, diabetes, cancer, and obesity

Types of Genetic Disorders 3. Chromosomal –abnormalities in chromosome structure as missing or extra copies or gross breaks and rejoining Example: Down Syndrome

Types of Genetic Disorders 4. Mitochondrial –rare type of genetic disorder –caused by mutations in the non-chromosomal DNA of mitochondria

Here are some genetics disorders, some you have heard about and some you haven’t.

Turners Syndrome 1 in 5,000 births 45 chromosomes X only #23 Monosomy Nondisjunction

Turners Syndrome 96-98% do not survive to birth No menstruation No breast development No hips Broad shoulders and neck

Cri-Du-Chat Syndrome 1 in 216,000 births 46 chromosomes XY or XX #5 Deletion of lower arm

Cri-Du-Chat Syndrome Moon-shaped face Heart disease Mentally retarded Malformed larynx Normal lifespan

Aniridia-Wilms Tumor Syndrome 1 in 50,000,000 births 46 chromosomes XY or XX #11 Deletion of upper arm

Aniridia-Wilms Tumor Syndrome Mentally retarded Growth retarded Blindness Tumors on kidneys Short lifespan

Thirteen Q Deletion Syndrome 1 in 500,000 births 46 chromosomes XY or XX #13 Deletion of lower arm

Thirteen Q Deletion Syndrome Mentally retarded Deformed face No thumbs Heart disease Short lifespan

Prader-Willi Syndrome 1 in 5,000,000 births 46 chromosomes XY=97% XX=3% #15 Deletion of lower arm

Prader-Willi Syndrome Small bird-like head Mentally retarded Respiratory problems Obesity Short lifespan

Eighteen Q Deletion Syndrome 1 in 10,000,000 births 46 chromosomes XY or XX #18 Deletion of lower arm

Eighteen Q Deletion Syndrome Mentally retarded Heart disease Abnormal hands and feet Large eyes Large ears Normal lifespan

Cat-Eye Syndrome 1 in 1,000,000 births 46 chromosomes XY or XX #22 Deletion of bottom arm

Cat-Eye Syndrome Fused fingers and toes Mentally retarded Small jaw Heart problems Normal lifespan

Four-Ring Syndrome 1 in 10,000,000 births 46 chromosomes XY or XX #4 Inversion

Four-Ring Syndrome Cleft palate Club feet Testes don’t descend Short lifespan

Down Syndrome 1 in 31,000 births 46 chromosomes XY=97% XX=3% #14/21 Translocation 1 in 1,250 births 47 chromosomes XY or XX #21 Trisomy Nondisjunction Down Syndrome Trisomy

Down Syndrome Short, broad hands Stubby fingers Rough skin Impotency in males Mentally retarded Small round face Protruding tongue Short lifespan

Patau’s Trisomy Syndrome 1 in 14,000 births 47 chromosomes XY or XX #13 Trisomy Nondisjunction

Patau’s Trisomy Syndrome Small head Small or missing eyes Heart defects Extra fingers Abnormal genitalia Mentally retarded Cleft palate Most die a few weeks after birth

Edward’s Trisomy Syndrome 1 in 4,400 births 47 chromosomes XX=80% XY=20% #18 Trisomy Nondisjunction

Edward’s Trisomy Syndrome Small head Mentally retarded Internal organ abnormalities 90% die before 5 months of age

Jacob’s Syndrome 1 in 1,800 births 47 chromosomes XYY only #23 Trisomy Nondisjunction

Jacob’s Syndrome Normal physically Normal mentally Increase in testosterone More aggressive Normal lifespan ?

Klinefelter Syndrome 1 in 1,100 births 47 chromosomes XXY only #23 Trisomy Nondisjunction

Klinefelter Syndrome Scarce beard Longer fingers and arms Sterile Delicate skin Low mental ability Normal lifespan

Triple X Syndrome 1 in 2,500 births 47 chromosomes XXX only #23 Trisomy Nondisjunction

Triple X Syndrome Normally physically Normal mentally Fertile