Human Genetics:Human Genetics:Patterns of Inheritance for Patterns of Inheritance for

Human TraitsHuman Traits

We will be discussing 5 Patterns of We will be discussing 5 Patterns of Inheritance for Human TraitsInheritance for Human Traits

1. Single Allele Dominant1. Single Allele Dominant

2. Single Allele Recessive2. Single Allele Recessive

3. Sex Linked (X-Linked)3. Sex Linked (X-Linked)

4. Multiple Alleles 4. Multiple Alleles

5. Polygenic Traits5. Polygenic Traits

Single Allele GenesSingle Allele GenesRegular traits that are either determined by a Regular traits that are either determined by a

dominant or recessive allele on an autosomedominant or recessive allele on an autosome

1.1. Autosomal Dominant examples: Autosomal Dominant examples: a. Huntington’s Disease a. Huntington’s Disease b. Achondroplasia (dwarfisim)b. Achondroplasia (dwarfisim)c. Polydactyly (extra fingers and toes)c. Polydactyly (extra fingers and toes)

2. Autosomal Recessive examples: 2. Autosomal Recessive examples: a. Albinisma. Albinismb. Cystic Fibrosisb. Cystic Fibrosisc. Sickle Cell Anemiac. Sickle Cell Anemia

1. Dominant Allele Disorders1. Dominant Allele DisordersHuntington’s Disease (HD)Huntington’s Disease (HD) Results in loss of muscle Results in loss of muscle

control and mental control and mental deteriorationdeterioration

No signs are shown until No signs are shown until 30’s30’s

Brain degenerationBrain degeneration Treatment: No cure, but Treatment: No cure, but

drug treatments are drug treatments are available to help manage available to help manage symptoms.symptoms.

1. Dominant Allele Disorders1. Dominant Allele Disorders

Achondroplasia Dwarfism Person grows no

taller than 4’4

1. Dominant Allele Disorders1. Dominant Allele Disorders

PolydactylyPolydactyly The presence of more The presence of more

than the normal than the normal number of fingers or number of fingers or toes. toes.

Can usually be Can usually be corrected by surgery.corrected by surgery.

2. Recessive Allele 2. Recessive Allele DisordersDisorders

AlbinismAlbinism Lack of pigment in Lack of pigment in

skin, hair, and eyesskin, hair, and eyes Mutation in one of Mutation in one of

several genes which several genes which provide the instructions provide the instructions for producing one of for producing one of several proteins in several proteins in charge of making charge of making melanin.melanin.

2. Recessive Allele 2. Recessive Allele DisordersDisorders

Cystic Fibrosis (CF)Cystic Fibrosis (CF) Caused by recessive Caused by recessive

allele on chromosome 7allele on chromosome 7

Small genetic change Small genetic change (removes one Amino (removes one Amino Acid) Acid) changes changes proteinprotein

Results in: Excess Results in: Excess mucus in the lungs, mucus in the lungs, liver and digestive liver and digestive tract, gets infection tract, gets infection easily, and early death easily, and early death unless treated.unless treated.

2. Recessive Allele 2. Recessive Allele DisordersDisordersSickle Cell DiseaseSickle Cell Disease Red blood cells are Red blood cells are

bent and twistedbent and twisted Get stuck in Get stuck in

capillaries capillaries damage damage tissuestissues

Results in weakness, Results in weakness, damage to brain and damage to brain and heartheart

3. Sex Link Traits:Genes on the X and Y

chromosomes

Human Chromosomes: Human Chromosomes: 2 Sex 2 Sex ChromosomesChromosomes

Human Chromosomes: Human Chromosomes: 2 Sex 2 Sex ChromosomesChromosomes

Human Chromosomes:Human Chromosomes:44 Autosomes44 Autosomes

Human Chromosomes:Human Chromosomes:44 Autosomes44 Autosomes

Gender We determine the gender of

an individual through sex chromosomes

Sex Chromosomes: X and Y Female: XX

Male: XY

• The father gives an X or Y to the gametes. The mother only gives an X to the gamete

The X chromosome is larger than the Y chromosome.

What are sex-linked genes? genes found on a sex chromosome• X-linked genes are genes

found on the X chromosome, symbolized by Xr, XR, Y0.

• Y-linked genes are found on the Y chromosome, symbolized by X0, YR, Yr

Sex-Linked Traits• It is possible for a

female to be a carrier of an X-linked trait, but not express it

• Men will express all X-linked traits they inherit because they have one X chromosome

X-linked recessive, carrier mother

Unaffectedson

Unaffecteddaughter

Affectedson

Carrierdaughter

Unaffectedfather

Carriermother

Carrier

Affected

Unaffected

X-linked Genes

• Let’s do a punnett square for a female carrier of an x-linked gene and a recessive male

• What will the genotypes be?

• XRXr and XRY

Here’s the results

• For girls: 0% have the trait

• For boys 50% have it.• Probability is higher

for boys because whatever X they get determines the trait, for girls they have to get 2 recessive X’s.

XR Xr

XR XR XR XR

Xr

Y0 XR Y0 Xr Y0

Examples of X-linked traits:

1. Color Blindness

2. Hemophilia

3. Muscular Dystrophy

4. Icthyosis simplex (scaly skin)

Colorblindness

• A person with normal color vision sees a number seven in the circle above.

• Those who are color blind usually do not see any number at all.

Colorblindness• RED-GREEN

COLORBLINDNESS:

• People with red-green color blindness see either a three or nothing at all.

• Those with normal color vision see an 8.

Hemophilia

Hemophilia- Lacking in the ability to clot blood– There is a gene on

the “X” chromosome that control blood clotting

– People who have hemophilia are missing the protein to clot blood

– They can bleed to death by minor cut.

Muscular Dystrophy

- Results in weakening/loss of muscles

- Caused by defective version of gene that codes for muscle

Sex-influenced Traits

• Sex-Influenced traits are those that are on autosomes, but occur because of the sex hormones in male and female bodies.

• Examples: Facial hair

Baldness

4. Multiple Alleles4. Multiple Alleles Multiple AllelesMultiple Alleles – any gene that has 3 or – any gene that has 3 or

more alleles (not just 1 dominant and 1 more alleles (not just 1 dominant and 1 recessive)recessive)

Example: Blood type has 3 alleles:Example: Blood type has 3 alleles:

IIAA= Type A blood (dominant)= Type A blood (dominant)

IIBB= Type B blood (dominant)= Type B blood (dominant)

i = Type O blood (recessive)i = Type O blood (recessive)

Check out the possible genotypes Check out the possible genotypes and phenotypes of blood below:and phenotypes of blood below:

Genotypes Phenotypes

IAIA or IAi Type A

IBIB or IBi Type B

IAIB Type AB

ii Type O

Blood has both Blood has both Multiple AllelesMultiple Alleles and is and is CoDominantCoDominant

• If you have IIf you have IAAIIBB as your genotype, you as your genotype, you have both Type A and Type B blood, have both Type A and Type B blood, also known as Type AB also known as Type AB

• If you have IIf you have IAAi, i is recessive i, i is recessive to Ito IAA, so you have type A blood, so you have type A blood

• Q. When would you have Type O blood?Q. When would you have Type O blood?

• A. When you have ii as your genotype.A. When you have ii as your genotype.

5. Polygenic Traits – traits controlled by 2 or more genes that interact, forming the trait Usually show a wide range of phenotypes Ex: Skin color, eye color, foot size, height

– Wide range of skin colors because there are more than 4 genes that control this trait.

These may also be influenced by the environment, for example height. If not given the proper nutrition as a child, they might not be as tall as their genes dictate.