Chromosome Inheritance Flashcards
How many chromosomes do genetically normal humans possess?
22 pairs of autosomes and 1 pair of sex chromosomes
Nondisjunction
a failure of homologous chromosomes or daughter chromosomes to separate correctly during meiosis I and meiosis II
What does nondisjunction result in?
Trisomy — 3 copies of one chromosome in normal body cells; usually fatal except for chromosome 21(Down’s Syndrome)
Monosomy — 1 copy of a chromosome in normal body cells; fatal except for X chromosome
Barr Body
a darkly stained mass of chromatin that is inactive
– in genetically typical XX females, one of the X chromosomes becomes a Barr Body
Turner Syndrome
XO
– when an individual one has one X chromosome so no Barr Body forms but the cells otherwise function as normal
What are some characteristics of an individual with Turner Syndrome?
–short stature, broad chest, folds on the skin on the back of the neck
– ovaries, uterine tibes, and uterus are small and underdeveloped
Jacob’s Syndrome
XYY
– viable because the Y sex chromosome is so small that it carries relatively little genetic information
– occurs during nondisunction during meiosis II
What are some characteristics of an individual with Jacob’s syndrome?
– taller than average male
– persistent acne
– speech and reading difficulties
– normal fertility
Klinefelter Syndrome
XXY or XXXY
extra X chromosomes become barr bodies
What are some characteristics of an individual with Klinefelter Syndrome?
– underdeveloped testes and prostate
– limited facial hair
– some breast development
– large hands and feet, and very long arms and legs
– slow learners
– sterility
Poly X Syndrome
XXX or XXX+
has extra barr bodies in the nucleus
What are some characteristics of an individual with Poly X Syndrome?
— sometimes delayed motor and language development
– tall and thin
– menstrual difficulties
– infertility
