M1 L4: Pedigree Analysis

• Pedigree


  A family tree that describes the interrelationships of parents and children across generations
• Pedigrees are used by professionals to analyze the pattern of inheritance of a particular trait throughout a family for medical purposes
• Pedigrees can be used to make predictions about future offspring
• Autosomal Traits

  46 autosome; 2 sex chromosomes
• Standardized symbols used in pedigrees

  • CIRCLE: female
  • CROSSED OUT: deceased
  • SQUARE: male
  • SPLIT LINE  2 SHAPES: twins
  • SHADED SHAPE: affected with trait
  • SHAPE W/ BRACKETS O: adopted
  • HALF SHADED SHAPE: carrier of trait
  • TRIANGLE: miscarriage
• Widow's peak is dominant. Dad can't pass sex-linked trait to son (XY), only to his daughter (XX). However, they have a son with a widow's peak, indicating it isn't an X-linked trait
• A child's gender depends on the father's sperm (X or Y) since the egg cell always carries X
• X sperm is slow but can survive longer, Y sperm is fast but dies faster
• Can only determine homozygous or heterozygous alleles when individuals have children and express a dominant trait
• Females who are homozygous and males who are hemizygous express the phenotype in X-linked recessive inheritance
• An affected mother passes the trait to all offspring but only sons exhibit the phenotypes in X-linked recessive inheritance
• An affected father passes the trait to all daughters but to none of his sons in X-linked recessive inheritance
• Individuals with the dominant allele on the X chromosome exhibit the phenotype
• An affected male passes the allele to all daughters but to none of his sons
• An affected female passes the alleles to all offspring unless she is a heterozygote
• Linked genes tend to be inherited together because they are located near each other on the same chromosome
• Genes located on the same chromosome tend to be inherited together and are called linked genes
• Non-parental phenotypes are produced in the test cross through genetic recombination
• Identical twins result from one sperm and egg cell dividing during cell division
• Conjoined twins were unable to fully divide during cell division
• Fraternal twins result from 2 egg cells fertilized by different sperm cells
• Large-scale chromosomal alterations in humans and other mammals often lead to spontaneous abortions
• In nondisjunction, pairs of chromosomes do not separate properly during meiosis
• Alterations of chromosome number or structure cause some genetic disorders
• Nondisjunction


  Pairs of homologous chromosomes do not separate normally during meiosis
• If nondisjunction happens during meiosis 1, it is more severe with: 2 gametes with extra, 2 gametes with missing chromosomes
• As a result of nondisjunction, one gamete receives two of the same type of chromosome, and another gamete receives no copy
• Aneuploidy results from the fertilization of gametes in which nondisjunction occurred
• Offspring with aneuploidy have an abnormal number of a particular chromosome
• A monosomic zygote has only one copy of a particular chromosome, often leading to miscarriages
• A trisomic zygote has three copies of a particular chromosome, with a higher survival rate
• Polyploidy is a condition in which an organism has more than two complete sets of chromosomes
• Polyploidy is common in plants but not animals
• Polyploids are more normal in appearance than aneuploids
• Down syndrome (Trisomy 21) results from 3 copies of chromosome 21
• Down syndrome affects about one out of every 830 children born in the United States
• The frequency of Down syndrome increases with the age of the mother
• Klinefelter syndrome results from an extra X chromosome in males, producing XXY individuals
• Trisomy X or XXX females occur with a frequency of about one in 1,000 and are at risk for learning disabilities
• Monosomy X, called Turner syndrome, produces X0 females who are sterile