Human Heredity

Who and What and Why of Humans?

New Flash……..

 

It has been discovered that having a glowing “red nose” is a recessive sex-linked trait in Reindeer….. AND….the strange ability to fly is also a recessive autosomal trait…..

 

Deep within the Taiga, two adult consenting Reindeer mate…… the male is homozygous recessive and thus has the ability to “fly”…. But has a normal black nose………

The female is a sex linked carrier for “red glowing nose”…but her phenotype is black nose….and she is heterozygous for flying ability….thus cannot fly……

 

Can these two Reindeer create Rudolph??

What about Rudolpha??

SHOW YOUR WORK…..

Key, parents, gametes, Punnett square, results…….

Dominant Genes in Humans

• Simple Dominant Traits (A)

– -Huntington’s disorder

– Free hanging earlobes = dominant

– Polydactyly (more than five digits) = dominant

– -Right handed over left handed

Huntington’s Disease – Dominant Gene

A lethal disease caused by A rare dominant gene.

– Nervous system degenerates.

» Uncontrolled, jerky movements

• No treatment -

• Onset occurs in the thirties so they could have passed it on to their children-

• 1 in 10,000

Recessive Genes in Humans (a)

• Cystic Fibrosis - the most common lethal genetic disorder among white Americans.– 1 in 25 white Americans carries it. (Aa)

– The mucus in the lungs is particularly thick.

– Breathing is difficult because mucus collects in the lungs.

Recessive Genes in Humans (b)• Sickle-cell anemia - most

common recessive gene found in African Americans.

– 1 in 500 African Americans is a carrier (Bb)

– Red blood cells are sickle shaped.

– The red cells cannot carry oxygen as well when sickled.

– Cells can clog the blood vessels.

– Does decrease the chances of malaria infection

Recessive Genes in Humans (f)

• Tay-Sachs Disease - is a disease to the central nervous system.

• Occurs in the Jewish population. (Ff) – Lipids ( fat ) are broken down by an enzyme.

– People with Tay-Sachs do not produce this enzyme.

– Lipids (fats) build up in the brain .

– And results are a loss of movement, blindness and mental deterioration.

– Death occurs before the age of five. ( ff )

Multiple Alleles ( A, B , O)

• Blood Groups - blood types are determined by three different alleles- A, B, O– The Blood gene (I) has three different alleles

• A = A blood - A surface molecule

• B = B blood - B surface molecule

• O = O blood - no surface molecule - recessive

Both codominant

Phenotype

IA IBIA IA IAi A Blood

IB IB I B i B Blood

i i O Blood

Genotype Phenotype

AB Blood

Genotype

Polygenic Traits

• There are thousands of traits in humans in where many genes ( polygenic ) combine to form one trait.

• As many as 12 or more genes acting together to produce…..– Eye color

– hair color

– skin color

– Foot size

Sex-Linked Traits

• Males are XY• Females are XX• The Y chromosome does not have the genes to

mask the genes that are on the X chromosome• Examples are

– Red Green Color Blindness

– Hemophilia

Red - Green Color Blindness

• People with red-green color blindness can not see the difference between these two colors

XR Xr

Y

XR XR XR XR Xr

Xr YXR Y

Female Carrier

Mal

e N

orm

al

Hemophilia

• Hemophilia is a sex-linked disease in which a person is unable to clot their blood when they cut or bruise themselves.

• The family of Queen Victoria is best known for this disease.

XH

Xh

Y

XH

XH XH

XH Y Xh Y

XH Xh

Female CarrierM

ale

Nor

mal

Male Normal

Female Normal Female Carrier

Male Hemophiliac

What determines the sex of the offspring???

• The 23rd pair of chromosomes are called the sex chromosomes.

• In the male , they are X and Y• In the female they are X and X

• X Y• X• X

Mistakes in Meiosis• In meiosis there is a

chance that some pairs of chromosomes will not split.– This causes the chance

of Trisomy– ( 3 chromosomes of a

certain chromosome )

– Karyotype is a picture of all the chromosomes.

– It is determined by Amniocentesis, a sample of amniotic fluid from the uterus

Nondisjunction

• The failure of a chromosome pair to separate during meiosis.

• Down’s Syndrome is a disorder where no separation of the pair chromosome 21.– This causes the sperm or

egg to carry 24 chromosomes.

– Occurs in a higher amount to mothers over 40

– Also called – Trisomy 21

3 chromosome 21’s