Human Genetics

Chapter 14-1, 14-2Human Heredity

Human Genome

• 3 billion base pairs– 6 billion individual bases

• “4 million pages”• Bases (letters) spell out

genes (words) that result in the phenotype (the story)

• Some spell out bad stories (diseases)

What do you see?

Colorblindness is an example of a sex-linked disorder

• h = hemophilia, a sex-linked disorder

• For each, can you answer…• Is the dad affected?• Is the mom affected?• How many children have the

disease?• How many children are carriers?• How many children are healthy?

(careful!)

PEDIGREES another way to study inheritance

• What do you think the F1 generation (line II) # 2 and #5 offspring represent?

• Can you draw the Punnett Square for the Parent generation? (I)

How to read a pedigree…

Carrier female

Carrier male

Pedigrees• Show how traits are passed down through

many generations• Based mostly on phenotypes• Show the actual offspring– Punnett squares show the possible offspring

• Really only works well for single traits– Not polygenic traits

• Only works for inherited traits– Environmental factors play a large role in who we are

Inheriting Diseases

• Just like physical traits, some diseases can be inherited on our chromosomes.

• And, just like physical traits, some are X-linked, some are recessive, some are dominant or codominant.

Genetic Disorder Fact Sheet topicsFragile x syndrome

Gaucher diseaseDuschene Muscular Dystrophy

Marfan syndromeColor blindness

Hurler syndrome

Tay-SachsAlbinism

Cystic FibrosisSickle cell anemia

PKULou Gehrig’s disease

Cri du Chat syndromeHuntington DiseaseTurner’s syndrome

Klinefelter syndromeDown syndromeFanconi anemia

Other Chromosomal Actions

• X-Inactivation if men only need one X chromosome, do women need both X’s? – If not, which one “works”?

• Non-disjunction how gametes can end up with the wrong # of chromosomes in meiosis

X-Chromosome Inactivation

• Men are XY: One X chromosome is enough• Women are XX: The “extra” copy is not needed.

It condenses into a “Barr body.” • Remember, you have trillions of cells. Which X

chromosome that “switches off” can vary in each cell!

Mosaicism

Nondisjunction• “Not coming apart”• Homologous

chromosomes fail to separate in meiosis

• Result in Trisomy or Monosomy

• Examples: – Klinefelter syndrome (trisomy

X)– Down syndrome (trisomy 21)– Turners syndrome (X_

monosomy)

• Click the image to play the video segment.

Video 2

Nondisjunction