Inquiry Into Life Chapter 24
check in: describe the phenotypic ratio that is expected for a cross in which both parents have one x-linked recessive allele.
50% of females and 50% of male offspring would express the recessive allele.
Cri du chat syndrome
A deletion on chromosome 5; infant cry that resembles a meowing cat.
Pedigree
A diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next
Huntington disease
A trinucleotide repeat of CAG disorder
Linkage group
All of the genes on one chromosome that tend to be inherited together and do not show independent assortment. Broken only when crossing-over occurs.
Deletion
Change in chromosomal structure in which the end of a chromosome breaks off or when two simultaneous breaks lead to the loss of an internal chromosomal segment. Example of syndrome: cri du chat syndrome.
Sex chromosomes
Chromosomes that differ between sexes. Males have the sex chromosomes X and Y, and females have two X chromosomes.
X linked Recessive Disorders
Color Blindness, fragile X syndrome, hemophilia, Duchenne muscular dystrophy
Translocation
Exchange of chromosomal segments between two non-homologous chromosomes
Turner syndrome
Female with only one X chromosome (and no Y). Usually short, webbed neck, no secondary sex characteristics at puberty without hormone therapy, normal intelligence.
Poly-X syndrome
Female with three or four X chromosomes and no Y
Jacobs syndrome
Male XYY, results from nondisjunction during spermatogenesis.
Klinefelter syndrome
Male with two X chromosomes and one Y (XXY), who develop severe symptoms as adults. Speech and language delays, no secondary sex characteristics at puberty without hormone therapy.
homologous chromosomes
Pair of chromosomes that are alike
Barr body
The darkly stained inactive X chromosome in a female
Sex-linked; X-linked
Traits controlled by genes on sex chromosomes. If on an X chromosome, X-linked. Most sex linked disorders are carried on the X chromosome.
Patau Syndrome
Trisomy 13. Cleft palate, polydactylism, babies rarely survive. Autosomal.
Edwards syndrome
Trisomy 18. Mental retardation, heart problems, distinctive hands and feet. Babies rarely survive. Autosomal.
Monosomy
When an egg with 22 chromosomes is fertilized by a sperm, resulting in one chromosome having only one copy
Trisomy
When an egg with 24 chromosomes is fertilized by a sperm, resulting in one chromosome having three copies. The most common autosomal trisomy in humans is Down Syndrome, also called Trisomy 21.
Chromosomal mutations
When chromosomes break as a result of: radiation, organic chemicals, or viruses and fail to reunite correctly.
Sex linked Alleles
When considering X linked traits, the allele on the X chromosome is shown as a letter attached to the X chromosome.
A male always receives an x linked allele from his mother because
Y chromosome from father does not carry an allele for the trait.
Nondisjunction
a failure of the chromosomes or sister chromatics to separate during meiosis.
Fragile X Syndrome
abnormal number of repeat sequences in the genome: trinucleotide repeat of CGG. Most common cause of inherited mental impairment. X-linked recessive disorder.
Hemophilia
blood clotting disorder. X-linked recessive disorder.
Duplication
change in chromosomal structure in which a chromosomal segment is repeated in the same chromosome.
Inversion
change of chromosomal structure in which a segment of chromosome is turned 180 degrees
Williams Syndrome
chromosome 7 loses a tiny end piece (deletion). Children look like pixies (turned up noses, wide mouths, large ears).
check in: summarize the causes of the X-linked recessive disorders discussed in this chapter.
color blindness: 8% of Caucasians perceive red and green colors differently. Duchenne muscular dystrophy: cause by the absence of the protein dystrophin, which leads to calcium entering the cell, which promotes an enzyme that dissolves muscle fibers. Fragile X: an abnormally high number of repeat sequences of CGG on the X chromosome. Hemophilia: either due to the absence or low level of clotting factor VII or factor IX, resulting in a reduced ability of the blood to clot.
Trinucleotide
having over 40 copies of the CAG sequence. Known in the Huntington Disease
color blindness
inability to properly distinguish colors; x-linked recessive disorder
Inv dup 15 syndrome
inverted duplication of chromosome 15; causes poor muscle tone and autistic characteristics
Detect chromosomal abnormalities
karyotyping, amniocentesis, and chorionic villus sampling
Down syndrome (trisomy 21)
most common autosomal trisomy in humans. More likely to occur in older moms (high risk over 40). Easily recognized characteristics including short statute, flat face, upward slat of eyes, crease on palm of hand, mental impairment. 47 chromosomes (one extra 21--three copies).
Mononsomy
result of only one type of chromosome present in a single copy
check in: how do sex-linked patterns of inheritance differ from autosomal inheritance?
sex-linked inheritance is dependent on the distribution of the X and Y chromosomes in males and females.
Autosomes
the 22 non sex-linked chromosomes. (Normally, both males and females have 23 pairs; the other pair is sex chromosomes)
During independent assortment,
the chromatids exchange genetic material, and therefore genes.
karyotype
the display of chromosome pairs arranged and numbered according to their size from largest to smallest (see fig. 24.7). created by retrieving cells, adding dye during metaphase, matching homologous pairs by banding patterns.
Maleness
the presence of the Y chromosome, not the X determines
Duchenne muscular dystrophy
x-linked recessive disorder characterized by wasting away of muscles