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

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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 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.

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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 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

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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