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