Chapter 3 Exam 2 Flashcards
What are chromosome arms?
All human chromosomes have 2 arms - the p (short) arm and the q(long) arms.
Where are telomeres found in humans?
A telomere is a region of repetitive nucleotide sequence at the end of each chromatid
What is the sequence of nucleotides of telomeres in vertebrates?
TTAGGG
What are the variations in chromosome numbers among primates and other species?
Humans have 46 chromosomes (diploid number). Chimps and gorillas have 48. Other organisms vary anywhere from 8-78
What does the synteny of gene order on chromosomes in different species do?
Synteny is a comparison between the genes of two different species when the chromosome has large blocks where the chromosomes have the same gene order
How did the evolution of human chromosome two occur?
Human chromosome two arose from a fusion of two chromosome following a translocation
What are homologous chromosomes?
Homologous chromosomes are made up of chromosome pairs of approximately the same length, centromere position, and staining position
What is nondisjunction?
Nondisjunction is the failure of chromosomes to separate properly during cell division. Nondisjuction may occur during mitosis. This results in Aneuploidy
What is aneuploidy?
An abnormal number of chromosomes, at least one missing or one extra
What is euploidy?
Normal number of chromosomes, two copies of each chromosome
What is trisomy?
3 copies of one chromosome. Only three autosomal trisomies result in live births. Mental disabilities, spontaneous abortion, and early death is typical with trisomy
What is monosomy?
Only one copy of a chromosome. Monosomy of ay autosome is fatal
What is the gene dosage issue?
The normal gene dosage is two copies for each autosomal gene. For normal expression the zygote needs one chromosome from each parents, if both copies of a single chromosome are inherited from a single parent or there is a deletion of one of these region in the chromosomes fromk one parent then there is a gene dosage problem
What is the connection between maternal age and trisomy/monosomy?
Maternal age is the leading risk factor for having a trisomic child. Explanations: older eggs have increased risk of nondisjunction or may be damaged. There may be changes in ‘maternal selection’ more aneuploidy embryos are allowed to implant with fewer aneuploids available
What is Trisomy 13?
Also known as Patau Syndrome. 47 chromosomes with the extra found on the 13th chromosome. Occurs 1/15000 births, survival is 1-2 months and includes facial, eye, finger, toe, brain, heart and nervous system malformations
What is Trisomy 18?
Also known as Edwards Syndrome. 47 chromosomes with the extra found on the 18th chromosome. Occurs 1/11000 births with 80% in females. Survival is 2-4 months and includes being small, having mental disabilities, clenched fists, heart, hand and foot malformations. They typically die from heart failure or pneumonia
What is Trisomy 21?
Also known as Down Syndrome. 47 chromosomes with extra found on the 21st chromosome. Occurs 1/800 births (changes with the age of the mother). A major cause of childhood mental disabilities. Physical characteristics: wide, flat skulls; eyelid folds; large tongue; hear defects; physical and mental development problems. Survival to age 50
What is Monosomy XO?
Also known as Turner Syndrome. 46 chromosomes, is missing the second X or Y sex chromosome. Typically live to adulthood. Female phenotypic sex, short, wide-chested, underdeveloped ovaries, sterile, narrowing of aorta and normal intelligence. 1/10000 females births but most die before birth
What is Trisomy XXX?
47 chromosomes, an extra X sex chromosome
What is Trisomy XXY?
Also known as Klinefelter Syndrome. Most survive to adulthood, male phenotypic sex. Small breast development, small amounts of body hair, low fertility, may have mild learning disabilities. occurs 1/1000 males
What is Trisomy XYY?
Also known as Jacob’s Syndrome. Most survive to adulthood, normal male phenotypic sex and fertility. Average height, thin, good mental abilities but often severe adolescent acne. Many have mild or no symptoms. Occurs 1/1000 male births
What is amniocentesis?
A test used to identify whether or not a fetus has chromosomal abnormalities. Fetus must be 16+ weeks. Collects amniotic fluid, fetal cells grown in culture and karyotype produced, metabolites and fetal DNA can also be analyzed
What is Chorionic Villus Sampling (CVS)?
a test used to identify whether or not a fetus has chromosomal abnormalities. Fetus can be 10-12 weeks. Rapidly dividing cells removed from villi of chorion, karyotype can be obtained within a few days
What is Maternal blood sampling for fetal cells?
a test used to identify whether or not a fetus has chromosomal abnormalities. This is a newer procedure, allowing fetal cells or DNA or gene products in maternal blood to be detected
What is polyploidy?
Multiple sets of chromosomes. Triploidy and Tetraploidy
What is polyspermy?
the fertilization of the egg by two sperm
What is triploidy?
three sets of chromosomes (69), most common form of human polyploidy, makes 15-18% of all spontaneous abortions. 75% have two sets of paternal chromosomes, probably due to polyspermy. Lethal condition
What is tetraploidy?
Four sets of chromosomes (92). 5% of all spontaneous abortions, extremely uncommon in live births. Most result from failure of cell division in the 1st mitotic division of the zygote. Mosaics occur when the individual is a mixture of diploid and tetraploid cells
What are duplications?
a structural change in the chromosome that arises from either faulty meiotic recombination or faulty DNA repair. When a series of genes are repeated on the chromosome in exact order
What are deletions?
a structural change in the chromosome that arises from either faulty meiotic recombination or faulty DNA repair. When a gene on a chomosome is deleted
What are translocations?
A structural change in the chromosome that arises by either faulty meiotic recombination or faulty DNA repair. Two types of translocation occur
What is Robertsonian Translocation?
Centromeres from two nonhomologous chromosomes fuse and chromosomal material from the short arms is lost.• 5% of Down syndrome cases involve a Robertsonian translocation between chromosomes 21 and 14
What is reciprocal translocation?
Two nonhomologus chromosomes exchange parts, no genetic information is gained or lost, except possibly a pair of genes at the breakpoints
What are inversions?
a structural change in the chromosome that arises by either faulty meiotic recombination or faulty DNA repair. Usually there are no missing genes just a change in the gene order. People who are heterozygous for inversions have reduced fertility. Many of their offspring have more complicated chromosomal problems that come about after recombination during meiosis
What is Cri-du-chat syndrome?
cri-du-chat syndrome is caused by a deletion of the short arm of one chromosome #5 and leads to mental disabilities, characteristic facial appearance and gastrointestinal problems. Only the individuals who are heterozygous for the deletion have this phenotype. They have only one copy of the genes.
What is familial Down syndrome?
makes of 5% of Down syndrome cases. Due to a 14/21 chromosome translocation (if a pare is ‘’carrier’’ of a 14/21 chromosome there is a 1/3 risk of a Down syndrome child). Typically Down syndrome doesn’t run in families but translocation Down Syndrome does, it is an inherited condition
What is uniparental disomy?
both copies of a chromosome are inherited from a single parent
What is Prader-Willi syndrome?
children affected by Prader-Willi syndrome have two chromosome 15’s from their mother or are missing a piece from the paternal chromosome 15 and show a compulsive eating disorder and mental disabilities
What is Angelman syndrome?
children with this condition have two chromosome 15’s from their father or are missing a piece from the maternal chromosome 15 and have speech problems and mental disabilities
What does a genetic counselor do?
construct a detailed family history and pedigree. Share info that allows an individual or a couple to make informed decisions
