Download Chromosome Mutations

Autosomal Disorders
1. Deletion – piece of chr. lost
2. Insertion – piece of chr. added
3. Inversion – chr. segment breaks off & reattaches in reverse order
4. Translocation – chr. piece breaks off & gets added to different chr.
5. Nondisjunction – chr. do not separate during meiosis (anaphase I or II)
• gametes have an extra chr. OR missing a chr.
Nondisjunction in meiosis
Dihybrid (two-trait) Crosses = 16 squares!
*Used to predict inheritance of two unrelated traits
Example: In pea plants, the color yellow (Y) is dominant to green (y) and round texture (R) is
dominant to wrinkled (r). Give the phenotype ratios when you cross two plants with YyRr
genotypes.
Y = yellow
y = green
R = round
r = wrinkled
answer: YyRr x YyRr
*Determine all possible gametes of parents before Punnett square
*Even though there are 2 alleles for each trait, you only pass on 1 allele
*DO NOT PUT ONE LETTER PER ROW/COLUMN!!
Example: In pea plants, the color yellow (Y) is dominant to green (y) and round texture (R) is
dominant to wrinkled (r). Give the phenotype ratios when you cross two plants
with YyRr genotypes
answer:YyRr x YyRr
Human Genetics
AUTOSOMAL conditions: on chr. #1-22
Specific gene/chromosome locations:(include for genetic disorder newsletter)

1st number = the chromosome affected

p or q = above the centromere (p) or below the centromere (q)

2nd number = units above/below centromere
Ex: 12q24.1 = on the 12th chromosome, 24.1 units below centromere
Autosomal Disorders
1. Down’s Syndrome - (Trisomy 21)
• mental retardation, muscle weakness, heart defects, short
stature
• excess mucus clogs lungs & digestive system
• autosomal recessive
• Nondisjunction (extra chr. at #21)
2. Cystic fibrosis Chr#7
excess mucus clogs lungs & digestive system
• autosomal recessive
3. Sickle Cell Anemia Chr#11
• red blood cells are distorted crescent shape; unable to bind
oxygen properly
• autosomal recessive; child has if parents are carriers
4. Huntington’s Disease Chr#4
• deterioration of brain tissue in middle age (30’s-40’s)
• autosomal dominant; one parent must have disorder
Some general rules for identifying whether a disorder is
autosomal dominant:
1. At least 1 parent must have the disorder to pass it on.
The other parent may or may not have the disorder.
2. If both parents have the disorder, but are both heterozygous
the child may or may not get the disorder.
Some general guidlines for Autosomal recessive:
1. If both parents have the disorder, then all their offspring will
have the disorder.
2. A child can get the disorder from unaffected parents
if both parents are heterozygous and both give the recessive
allele (they are carriers)
3. Autosomal recessive disorders can stay hidden behind
dominant alleles for several generations.