Chromosomal Inheritance II Flashcards
Lesson 5
What are the effects of large-scale chromosomal alterations on phenotype?
Abnormal Chromosome Number (Down’s Syndrome)
Alterations of Chromosome Structure
nondistjunction
pairs of homologous chromosomes don’t separate normally during meiosis
What are the gametes if there is nondisjunction during Meiosis 1?
n+1, n+1, n-1, n-1
What are the gametes if there is nondisjunction during Meiosis 2?
n+1, n-1, n, n `
Aneuploidy
results from the fertilization of gametes in which nondisjunction occurred and results in monosomic (2n-1) and trisomic (2n+1) individuals
Why are some types of aneuploidy survivable, while most are fatal as a infant?
Some types of aneuploidy upsets the genetic balance less than others, resulting in individuals surviving
These individuals that survive have a set of symptoms (syndrome), characteristics of the type of aneuploidy
Down’s Syndrome
aneuploid condition that results from three copies of chromosome 21
Patau Syndrome
Trisomy 13; Eye, brain, circulatory defects. Children rarely live more than a few months
Edward’s Syndrome
Trisomy 18; Every organ system affected. Children rarely live more than a few months
Trisomy X
Three copies of the X chromosome, No major impacts of life expectancy, slightly taller than average (only females)
Klinefelter Syndrome
XXY aneuploidy, unusually small testes, sterile. Breast enlargement and other feminine body characteristics
Monosomy X
X0, The only known monosomy in humans. Phenotypically female, but sterile due to lack of female organ maturation
XYY Trisomy
Healthy and fertile, tend to be taller than average
What are accessory chromosomes?
Chromosomes present in some but not all individuals in a species that aren’t essential for survival
What is a 2-speed genome composed of?
Core chromosomes: carry essential genes that encode housekeeping functions- evolve slowly
Accessory chromosomes: show high mutation rates, the acquisition of foreign genes, copy number polymorphisms, and frequent rearrangements - evolve fast
