10.4 Study Guide Flashcards
What are the two main causes of chromosomal abnormalities?
- Incorrect Number of Chromosomes (Nondisjunction)
- Breakage of Chromosomes
How many of each chromosome should a normal gamete have? A normal zygote?
Gamete - 1
Zygote - 2
What is nondisjunction?
When chromosomes do not separate properly during Meiosis (or Mitosis).
What fails to separate if nondisjunction occurs in Meiosis I?
Homologous Chromosomes
What fails to separate if nondisjunction occurs in Meiosis II?
Sister Chromatids
How does nondisjunction occur in Meiosis I?
How does nondisjunction occur in Meiosis II?
Meiosis I - homologous chromosomes do not separate properly during Anaphase I.
Meiosis II - sister chromatids fail to separate during Anaphase II.
What is the result for the gametes if nondisjunction occurs in Meiosis I?
What about the Zygote?
Gametes will have abnormal chromosome numbers.
-Two gametes will have an extra chromosome
-Two gametes will be missing a chromosome
Zygotes will not be normal but would be diploid except for the extra or missing chromosome
What is the result for the gametes if nondisjunction occurs in Meiosis II?
What about the Zygote?
Gametes will have abnormal chromosome numbers.
- Two gametes will be normal
- One gamete will have an extra
chromosome
- One gamete will be missing chromosome
Zygotes could be normal or could be diploid except for the extra or missing chromosome
What is trisomy?
Cells that have 3 copies of 1 chromosome type. The cell is still diploid.
2n + 1
What is monosomy?
Cells that have only 1 copy of a chromosome. The cell is still diploid.
2n - 1
What are the three human trisomies?
- Trisomy 21 - Down Syndrome
- Trisomy 13 - Patau Syndrome
- Trisomy 18 - Edwards Syndrome
What Trisomy occurs in:
1 out of 700 children born in the US
The smallest human chromosome
and causes:
Heart defects, varying intellectual disabilities, vision + hearing problems, speech delay + difficulty
and is often correlated with the age of the mother (increasing risk significant after age 30 and worsening through age 49 where the odds are 1 in 12)
Down Syndrome (Trisomy 21)
An additional of one of chromosome 21 and a total of 47 chromosomes (47, 21+)
What trisomy occurs in:
mostly females
1 out of 8,000 live births
and causes:
fatality (normal 2.5 days after birth with only 5% surviving > 6months), severe neurological problems, facial abnormalities, malformed organs and polydactyly
and is associated with advanced maternal age
Patau Syndrome (Trisomy 13)
An additional of one of chromosome 13 and a total of 47 chromosomes (47, 13+)
What trisomy occurs in:
mostly females
1 out of 8,000 live births
and causes:
fatality (average age of death is 4 months with only 5-10% living beyond a year), elongated skull, low malformed ears, webbed neck, bad hips, bad heart, bad lungs
and is associated with advanced maternal age
Edwards Syndrome (Trisomy 18)
An addition of one of chromosome 18 and a total of 47 chromosomes (47, 18+)
What is an autosome?
Any chromosome that is not a sex chromosome.
Autosomes are responsible for carrying genes that determine most of an individual’s traits, excluding sex-linked traits.
How many pairs of autosomes do humans have? How are they numbered?
22 Pairs
Numbered 1 through 22
What are the other type of chromosomes humans have aside from autosomes? How many pairs does each human have?
Sex Chromosome
One pair - either XX or XY
Is human development more tolerant of the wrong number of autosomes or sex chromosomes?
Sex chromosomes
What is X-chromosome inactivation?
In females, one of the two X chromosomes is randomly inactivated in each cell during early embryonic development.
This ensures that females, who have two X chromosomes, don’t express twice the number of genes on the X chromosome as males, who have only one.
The inactive X chromosome condenses into a structure called a Barr body. This Barr body is a compact, transcriptionally inactive form of the inactive X chromosome.
What is a Barr Body?
A compact, transcriptionally inactive form of the inactive X chromosome
Found in the somatic cells of female mammals (those with XX chromosomes)
What Syndrome is the result of having the following sex chromosomes: XXY
This occurs in ___ of 2000 live births
Individuals have _____ sex organs, but are sterile. Some __________development and lack of facial hair. Are tall and of normal intelligence.
One of the X chromosomes becomes a Barr Body in each cell.
Klinefelter’s Syndrome
One
Male
Breast
Describe the sex chromosomes of someone with Jacob’s Syndrome.
This abnormality occurs in 1 in 1000 live ______ births.
Individuals are slightly taller than average, more active, normal to slightly lower intelligence, delayed emotional maturity and normal sexual development
XYY
Male
Trisomy of the X Chromosome (XXX) produces healthy females. Why?
Barr Bodies
All but one of the X chromosomes are inactivated.
Monosomy of the X Chromosome (X or X0) does not produce healthy females. What is the name of this syndrome?
This sex chromosome abnormality often causes spontaneous abortion and occurs in 1 of every 5000 births. Those who are born have varied effects including short stature, webbed neck, sterility and lack of sexual maturity.
Growth and sex hormones can help minimize effects if started earlier in life.
Turner Syndrome
