Chromosomes and their abnormalities Flashcards Preview

2020 MHS Genetics Unit2 > Chromosomes and their abnormalities > Flashcards

Flashcards in Chromosomes and their abnormalities Deck (38)
Loading flashcards...

Only have 23 nuclear chromosomes

Gametes- oocytes and sperm cells, have only 23 nuclear chromosomes (haploid)


designate this karyotype



designate this karyotype for male or female

47,XY,+21 or 47,XX,+21


designate the karyotype for robertsonian translocation downsyndrome

female and male

46,XX,rob(14;21), +21



designate the karyotype edwards syndrome for female and male

47,XX,+18 or 47,XY,+18


designate patau karyotype

47,XX,+13 or 47,XY,+13


designate the karyotype for cri du chat

46,XX,del(5p) or 46,XY,del(5p)


designate karyotype for klinefelter syndrome



designate the karyotype for turner syndrome

 45, X and 45,X/46,XX mosaics


what are the following types of chromosomes?

  1. P and q arms are clearly different lengths
  2. p and q arms are ~ equal lengths
  3. centromere is near one end 

  1. submetacentric
    1. p and q arms are clearly different length
  2. metacentric
    1. ~equal length of p and q arms
  3. acrocentric
    1. centromere is near one end


what is the segragation of sister chromatids?



abnormal chromosome seperation during meiosis



meitotic crossover ocurrs during what time of meiosis?

meitotic cell division - production of haploid gametes

  1. meitotic crossover (genetic recombination)
    1. increases genetic diversity
  2. occurs during meiosis1- P1


describe autosomal deletion syndrome:

  1. cause
  2. type of cry
  3. phenotypic expression


cri du chat

  1. caused by deletions in the p arm of chromosome 5:
    1. 46,XX,del(5p) or 47,XY,del(5p)
  2. cat like cry
  3. phenotypic expression
    1. intellectual disabilities
    2. growth retardation
    3. speech impairment
    4. heart problems
    5. small head
    6. narrow eyes , with greater than normal distance between them
    7. low-set ears


  • what are the increases in incidence of edwards?
  • what are the phenotypic expressions?


  1. incidence increases with mother's age
  2. phenotypic expression
    1. intellectual disabillities 
    2. failure to thirve
    3. congenital hear problems
    4. receding jaw
    5. low-set, malformed ear
    6. specifically clenching fist
    7. rocker-bottom feet


what chromosomes are considered for uniparental disomy? generate a flow chart examplifying the act of the UPD

take notice that a phenotype may be rescued from a UPD


what can be expected with most chromosomal abnormalities?

intellectual disabilities

developmental problems



what are the types of chromosomal abnormalities?

  1. abnormal chromosome number
  2. structural abnormalities
    1. balanced
      1. normal complement of chromosomal material
        1. ex: uneaqual crossover between chromosomes
    2. unbalanced
      1. there is missing or additional chromosomal material 
        1. deletions or insertions


total chromosome number is not a multiple of 23. What are the two types? discuss the compatability for life.


  1. trisomy
    1. abnormal (extra chromosome)
    2. most common: 
      1. x
      2. 21
      3. 18
      4. 13
  2. monosomy
    1. abnormal (missing chromosome)
    2. only turner syndrome patients are viable
      1. 45,X


most common genetic cause of intellectual disability.

what 5 ways to generate this phenotype?

down syndrome

  1. 47,XY,+21 or 47,XX,+21
  2. 46,XX,rob(14;21),+21 or 46,XY,rob(14;21),+21
  3. 46,XX,i(21q21q) or 46,XY,i(21q21q)
    1. isochromosome
    2. the logn arms of two chromosome 21s join together
  4. 46,XX/47,XX+21 or 46,XY/47,XY,+21
    1. occurs during embryonic develeopment. some cells are wild type and others are downs
  5. partial trisomy 21
    1. only part of chromosome 21 is present in triplicate
    2. one c'some is structural unbalanced


describe the sex-specific differentiation and phenotypic sex, pertaining to gonadal development

  • p arm
    • tetis dependent factor: expression of the SRY GENE ON THE Y CHROMOSOME induces male gonadal development
      • SRY is a transcription factor for TDF
    • very close to the telomeres and homologous region where gentic information between X and Y is shared
  • q arm
    • makes sperm and other genes


  1. what is increases the incidence of patau
  2. what are the phenotypic expressions




  1. incidence increases with mothers age
  2. phenotypic expression
    1. intellectual disabillities
    2. failure to thrive
    3. congenital heart problems
    4. sloping forehead
    5. cleft-lip
    6. polydactyly
    7. rocker bottom feet


describe the normal crossover and abnormal structural transnlocation between sex chromosomes. generate the genetypes and phenotypes

  1. Sex reversal-
    1. transfer of SRY from Y to X in sperm cells can produce XX male (gain of SRY) or XY female (loss of SRY) offsprings
  2. loss of function mutations in SRY also produces XY female offspring


What happens if there are more than one X c'somes in the human genome? 

if more than two X c'somes are present, all but one will be inactivated.

If one of the X c'somes is aberrant (substandard), it will be preferentially inactivated


what are 5 causes of sex reversals?

  1. Transfer of SRY from Y to X in male gametes
    1. generates 
      1. XX-male
      2. XY-female
  2. loss of function mutations of SRY
    1. XY-female
  3. DAX-1 gene duplication
    1. XY-female
  4. SOX 9 loss of function mutation
    1. XY-female
  5. SOX9  gene duplication
    1. XX-male


what is the function of SRY, DAX1 and SOX 9 expression?

DAX 1  and SOX9 are transcription factors and their expression leveles determine gonadal development

  1. SRY leads to SOX9 expression, which increases gonadal development
  2. DAX1 and SOX9 compete for development, which ever is expressed more determines the sex. 
    1. can cause sex reversal



what ensures similar X gene dosage between males and females

x chromosome inactivation (Xi)

silencing the genes of one X chromosome to ensure simlar X gene dosage between males and females


most of the unsilenced genes are on which side of the X c'some?

most unsilenced genes are on the distal end of the p arm (psudoautsomal region)


describe the process of X inactivation

  1. Inactivatio nis directed by the xinactivatio ncenter (XIC) that is located on the q arm of the X chromosome
  2. XIC produces a large non-coding RNA (XIST) that initiates changes in histone composition and DNA methylation of the chromosome. This causes the inactivation of most of the genes.
  3. X chromosome inactivation is not 100% 
    1. some genes remain active even on the inactivated chromosome
    2. most unsilenced genes are on the distal end of the parm
  4. Both X chromosomes are necessary for correct female sex development


when does X inactivation occur?

random- occurs during early embryogenesis

daughter cells in mitosis inherit the Xi pattern

females are mosaic for X-linked gene expression