Sex Linkages and Pedigree

Question 1

pedigree

Answer 1

• history of family in past generations where you can track incidents of a particular disorder
• danger of having close relatives–> recessive genes can come together in offspring

Question 2

Drosophia melanogaster (fruit fly)

Answer 2

• use because easy to manipulate genes, have lots of genetic history, short generation time, 10-14 days, large numbers of offspring, not many chromosomes (easy to track), easy to tell males and females apart (males have dark part)
• 8 chromosomes- number them the opposite way (smallest to largest)
• Y chromosome is bigger than X and has a hook- easy to see in microscope

Question 3

sex chromosomes

Answer 3

2X in female, XY in male

Y is responsible for sex of the offspring

Question 4

TH Morgan FINISH

Answer 4

• thought genes were carried on chromosomes

- standard genetic protocol

Question 5

reciprocal cross

Answer 5

• reveals how sex makes a difference

- if on X, defective gene cannot be passed from father to son (since father only passes Y)

Question 6

hallmarks of x-linked recessive inheritance

Answer 6

• an affected son can have parents who have normal phenotype (mother is a carrier)
• in order for a female to have the characteristic, her father must also have it. Mother must be a carrier
• the characteristic often skips a generation to the grandson (criss-cross inheritance)
• if a woman has a characteristic, all sons will have it
• ratio of affected individuals is skewed towards males

Question 7

color blindness

Answer 7

• sex-linked recessive , often x-linked (skewed to males)
• Colored in affected and heterozygous
• Can’t always tell without doing a genetic test (whether they are carriers)

Question 8

Duchenne muscular dystrophy

Answer 8

• x-linked recessive
• symptoms at 2-5 years old
• 1/10000 births- almost exclusively affects boys
• relatively high rate spontaneous mutation so not always received from parent
• protein- dystrophin (fast muscles- skeleton and cardiac)

Question 9

Hemophelia

Answer 9

• x-linked

- ex. Royal families in Europe

Question 10

G6PD

Answer 10

• x-linked
• Glucose 6 phosphate dehydrogenase
  Enzyme that creates NADPH (acts as reducing power) which eliminates reactive oxygen species (O with unpaired e- is highly reactive and can damage red blood cells)
• If you have a deficiency in this enzyme- may be protected from malaria
• many people are symptom free

Question 11

autosomal dominant

Answer 11

• affected children usually have affected parents
• heterozygous are affected
• 2 affected parents can produce an unaffected child
• 2 unaffected parents will not have an affected child
• male and female affected equally
  ex. Huntington’s

Question 12

Syndactyly

Answer 12

• autosomal dominant
• finger disorder
• Bones and all parts of fingers are there, fused together, and cut it open

Question 13

X-linked dominant

Answer 13

• ex. Hypertrichosis- having hair all over body
• X chromosome- dominant shows up more frequently in females since females have 2X
• Ratio is skewed toward females
• Atavistic- codes for trait that is more common in ancestors

Question 14

Atavistic Trait

Answer 14

• codes for trait that is more common in ancestors

- ex. Hypertrichosis, having a tail

Question 15

hair on ears

Answer 15

• Y-linked

- common in Indian men

Question 16

Rules of Pedigree Analysis

Answer 16

1. Count up all affected individuals and determine if the sex ratio is skewed one way or the other (If yes, then sex-linked recessive if more males, or dominant if more females; if no then autosomal)
2. See if parents of affected individuals are also affected (If yes, then dominant; if no then recessive)
3. Look for additional evidence that supports autosomal recessive (If trait reappears after a consanguineous mating; or if two affected individuals have all affected children)

Question 17

Tay Sachs disease

Answer 17

• neurodegeneration disease
• diagnosed at 2 years–> die at 5
• lysosomal storage disease
• without lysosome, component–>brain specific lipid- sphingolipid- accumulates
• -> causes neurons to stop being able to function normally
• occurs more often in Jewish populations, French Canadians (thought maybe forced inbreeding of population, exposes recessive gene)
• gene may have protected population against TB