Human Genetics Chapter 14-1, 14-2 Human 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 topics Fragile x syndrome Gaucher disease Duschene Muscular Dystrophy Marfan syndrome Color blindness Hurler syndrome Tay-Sachs Albinism Cystic Fibrosis Sickle cell anemia PKU Lou Gehrig’s disease Cri du Chat syndrome Huntington Disease Turner’s syndrome Klinefelter syndrome Down syndrome Fanconi 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)

Video 2 Click the image to play the video segment. Video 2 Nondisjunction