Genetics Lecture 23, 10/27 - Chapter 8: Chromosomal mutations, non disjunction, monosomy, trisomy

Chromosome Mutation: anytime you have a cell with an abnormal # of chromosomes. Typically this is the loss or gain of one chromosome.

• Monosomy: loss of one chromosome
• Trisomy: gain of a chromosome . . . 3 copies of a chromosome
• QUES: How does this happen? ANS: non-disjunction event during meiosis.
  
• Non-disjunction event explained: during anaphase when a chromosome pair is supposed to separate it fails to do so. Because of this you produce gametes which are not haploid. Your gametes are either diploid or empty for that particular chromosome.
• When you fertilize a diploid gamete you produce a trisomy. If a gamete without a copy of a chromosome is fertilized you will get a monosomy.
• Anueploidy - a condition of having one extra or one less copy of a single chromosome.
• Euploidy - condition where a cell has a complete extra haploid complement of chromosomes. EVERY CHROMOSOME
• Triploid - has 3 complements of chromosomes
• tetraploid - 4 haploid complements of chromosomes
• Result - broad phenotypic changes.

(13:05) Genetic mutations more in depth

• Monosomy: a condition of having one copy of a particular chromosome.
  
• Partial Monosomy: Cri-du-chat syndrome (cry of the cat)--> deletion of a large portion of the P arm on chromsome 5. Referred to as 46, -5p
• Anatomic abnormalities in the cardiac region as well as the gastrointestinal tract and mental retardation.
  
• Abnormal development of the glotis and the larynx. When these baby's cry they sound like cats.
• There is a correlation between the size of the deletion and the severity of the disease. The larger the deletion the worse the disease.
• (20:00) Trisomy: (more prevelant/common) presence of an extra copy.
• Trisomy 21 = Down Syndrome.
• series of syptoms associated with down syndrome
• affected individual - 6-8 of the traits
  
• affected individuals have a tendancy to look like each other.
• Traits: epicanthic fold over the corner of the eye. Flat face. Round head. Short. Some form of mental retardation. Short life span (avg into 50's)
• Typically the non-disjunction is in the ovum (95%). Correlation between occurency and the age of the mother at conception.
• If mom is 30 it is 1 in 1000.
• If mom is 40 it is 1 in 100
• If mom is 45 it is 1 in 50
• 35% of all births to a Mom above 40 result in Down Syndrome.
• (28:20) Why is there such a strong correlation between age of the mother and frequency of Down Syndrome?
• Females are born with all of their eggs - the eggs are with the mother since birth. Meiosis II happens during menstrul cycle and fertilization.
  
• (32:55) Trisomy 13 - Patau syndrome
• Infant is not mentally alert. High chance of being deaf. Clef Palate.
  
• Typically death occurs by 3 months.
• Upon autopsy you see a high degree of organ system malformation.
  
• Average age of the parents of Patau syndrome is 32.
• (36:45) Trisomy 18 - Edwards Syndrome
• smaller than average, elongated skull, congenital dislocation of the hip.
• Life expectancy is 4 months
• majority of affected infants are female.
• average age of parents of Edwards syndrome is 34.7

• Technically you can have a trisomy or a monosomy of any chromosome. It depends on which chromosome has a non-disjunction event. Embryos with these arrangments lead to early miscarrage.
• 15-20% of all conceptions end in miscarriage. Could be as high as 50% (mother doesn't even know she was pregnant)
• Of miscarriages, 30% have a chromosomal abnormality.
• 6% of all conceptions have a chromosomal abnormality.

• Post implantation (refers to time when it occurs). What happens: there is a system set up in which the embryo is, in effect, screened for abnormalities. If an abnormality is found your body will attempt to trigger a miscarriage. WHY? Basic answer is, conserve energy. Historically, there was a high mortality rate for women during birth - body wants to preserve itself.
  

• Miscarriages are on the rise. WHY?
• People are delaying having children till later in life.
• Home pregnancy tests - people are finding out they are pregnant sooner. (Schau's Theory)