Post on 03-Jan-2016
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
XX XY
XX XY
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 XHXh
Colorblind carrier XBXb
• 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)?
YXb
XB
Xb
XBXb
XbXb XbY
XBY
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)?
XB
XB
XBXb
XBXb XBY
XBY
Xb YPhenotype:
50% normal girls
50% normal boys
Parents: XBXB x XbY
?
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 DiseaseMiles 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.
?
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 chromosomesX only #23 MonosomyNondisjunction
Turners Syndrome
96-98% do not survive to birthNo menstruationNo breast developmentNo hipsBroad shoulders and neck
Cri-Du-Chat Syndrome1 in 216,000 births
46 chromosomesXY or XX
#5 Deletion of lower arm
Cri-Du-Chat Syndrome
Moon-shaped faceHeart diseaseMentally retardedMalformed larynxNormal lifespan
Aniridia-Wilms Tumor Syndrome
1 in 50,000,000 births
46 chromosomesXY or XX
#11 Deletion of upper arm
Aniridia-Wilms Tumor Syndrome
Mentally retardedGrowth retardedBlindnessTumors on kidneysShort lifespan
Thirteen Q Deletion Syndrome
1 in 500,000 births
46 chromosomesXY or XX
#13 Deletion of lower arm
Thirteen Q Deletion Syndrome
Mentally retardedDeformed faceNo thumbsHeart diseaseShort lifespan
Prader-Willi Syndrome1 in 5,000,000 births
46 chromosomesXY=97% XX=3%
#15 Deletion of lower arm
Prader-Willi Syndrome
Small bird-like headMentally retardedRespiratory problemsObesityShort lifespan
Eighteen Q Deletion Syndrome
1 in 10,000,000 births
46 chromosomesXY or XX
#18 Deletion of lower arm
Eighteen Q Deletion Syndrome
Mentally retardedHeart diseaseAbnormal hands and feetLarge eyesLarge earsNormal lifespan
Cat-Eye Syndrome
1 in 1,000,000 births
46 chromosomesXY or XX
#22 Deletion of bottom arm
Cat-Eye Syndrome
Fused fingers and toesMentally retardedSmall jawHeart problemsNormal lifespan
Four-Ring Syndrome
1 in 10,000,000 births
46 chromosomesXY or XX
#4 Inversion
Four-Ring Syndrome
Cleft palateClub feetTestes don’t descendShort lifespan
Down Syndrome
1 in 31,000 births
46 chromosomesXY=97%
XX=3%
#14/21 Translocation
1 in 1,250 births
47 chromosomesXY or XX
#21 Trisomy Nondisjunction
Down Syndrome Trisomy
Down Syndrome
Short, broad hands Stubby fingersRough skinImpotency in malesMentally retardedSmall round faceProtruding tongueShort lifespan
Patau’s Trisomy Syndrome
1 in 14,000 births
47 chromosomesXY or XX
#13 Trisomy Nondisjunction
Patau’s Trisomy Syndrome
Small headSmall or missing eyesHeart defectsExtra fingersAbnormal genitaliaMentally retardedCleft palateMost die a few weeks after birth
Edward’s Trisomy Syndrome
1 in 4,400 births
47 chromosomesXX=80%
XY=20%
#18 Trisomy Nondisjunction
Edward’s Trisomy Syndrome
Small headMentally retardedInternal organ abnormalities90% die before 5 months of age
Jacob’s Syndrome
1 in 1,800 births
47 chromosomesXYY only
#23 Trisomy Nondisjunction
Jacob’s Syndrome
Normal physicallyNormal mentallyIncrease in testosteroneMore aggressiveNormal lifespan
?
Klinefelter Syndrome
1 in 1,100 births
47 chromosomesXXY only
#23 Trisomy Nondisjunction
Klinefelter Syndrome
Scarce beardLonger fingers and armsSterileDelicate skinLow mental abilityNormal lifespan
Triple X Syndrome
1 in 2,500 births
47 chromosomesXXX only
#23 TrisomyNondisjunction
Triple X Syndrome
Normally physically
Normal mentallyFertile