Campbell Biology 10th Edition: Chapter 15 Flashcards

two alleles for a given character separate during gamete formation, and go to different gametes

alleles for different characters sort independently of each other during gamete formation

(1860) Genes are segments of DNA located along chromosomes

1875;1890s

• (1902) Walter S. Sutton, Theodor Boveri
• Genes occupy specific loci on chromosomes
• The chromosomes undergo segregation and independent assortment.

Provided the first solid evidence of a specific gene associating with a specific chromosome.

• Drosophila Melanogaster
• (eye color)
• (body color, wing shape)

Drosophila Melanogaster; 4; every 2 weeks

the phenotype for most organisms

1. Fly's eye color linked to it's sex
2. Gene involved in white-eyed mutant was located on the X chromosome only

law of segregation

law of independent assortment

the law of segregation: separation of homologs in anaphase I

the law of independent assortment: alternative arrangements of different homologous chromosome pairs in metaphase I

when the embryo is about 2 months old

• Gene on the Y chromosome required for the development of testes.
• In the absence of SRY, the gonads develop into ovaries.
• SRY codes for a protein that regulates other genes.

78 genes code for about 25 proteins

1,100 genes

1. color blindness
2. Duchenne muscular dystrophy
3. Hemophilia

term used in describing a males X-linked gene due to only one locus (XⁿY)

• 1/3500 males (US)
• progressive weakening of the muscles and loss of coordination
• absent muscle protein called dystrophin (gene for this protein located on X-chromosome)
• rarely live past early 20's

• absence of one or more of the proteins required for blood clotting
• bleeding prolonged because clot is slow to form
• treated with intravenous injections of the protein that is missing

• Inactivation of an X chromosome involves modification of the DNA and proteins bound to it, called histones, including attachment of methyl groups (--CH₃) to DNA nucleotides
• Two regions, one on each X chromosome, associate briefly with each other in each cell
• Gene called XIST (X-inactive specific transcript) becomes active only on the chromosome that will become the Barr body

A compact object of condensed inactive X found on the inside of the nuclear envelope.

When an organism has cells with more than one genotype

• Tortoiseshell gene is on the X chromosome
• Tortoiseshell phenotype requires the presence of two different alleles, one for orange fur and one for black fur.
• Only females can have both alleles, because only they have two X chromosomes.
• Orange patches are formed by populations of cells in which the X chromosome with the orange allele is active; black patches have cells in which the X chromosome with black allele is active.

genes located near each other on the same chromosome tend to be inherited together

the production of offspring with combinations of traits that differ from those found in either P generation parent.

an offspring whose phenotype matches one of the true-breeding parental phenotypes

an offspring whose phenotype differs from that of the true-breeding parental phenotypes

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end portions of two nonsister chromatids trade places; recombination of linked genes

Alfred H. Sturtevant; an ordered list of the genetic loci along a particular chromosome

the percentage of recombinant offspring; depends on the distance between genes on a chromosome

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a genetic map based on recombination frequencies

one of many Drosophila genes affecting eye color

the distances between genes; one map unit is equivalent to a 1% recombination frequency

locate genes with respect to chromosomal features, such as stained bands, that can be seen in the microscope

the members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II

an aberrant gamete that unites with a normal gamete at fertilization

2n-1; missing chromosome in zygote resulting from fertilization of normal gamete with one that has no copy of a particular chromosome

2n+1; extra chromosome in zygote resulting from fertilization of normal gamete with one that has an extra copy of a particular chromosome

...

more than two complete chromosome sets in all somatic cells

3n; three chromosome sets; may arise by the fertilization of an abnormal diploid egg produced by nondisjunction of all its chromosomes

4n; four chromosome sets; may arise from the failure of a 2n zygote to divide after replicating its chromosomes

bananas (triploid, 3n); wheat (hexaploid, 6n); strawberries (octoploid, 8n)

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1. errors in meiosis
2. radiation can cause breakage of chromosomes

1. deletion
2. duplication
3. inversion
4. translocation

chromosomal fragment is lost

the "deleted" fragment may become attached as an extra segment to a sister chromatid

a chromosomal fragment may also reattach to the original chromosome but in the reverse orientation

most common; nonhomologous chromosomes exchange fragments

less common; a chromosome transfers a fragment but receives none in return

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a set of traits characteristic of the type of aneuploidy

• trisomy 21 (extra chromosome 21)
• 1/830
• characteristic facial features, short stature, correctable heart defects, developmental delays
• increased chance of leukemia & Alzheimers
• lower rate of high blood pressure, atherosclerosis, stroke & many types of solid tumors
• life span: shorter than normal
• all males and half females are sexually underdeveloped & sterile
• frequency increases with mothers age (0.04% under 30)(0.92% at 40)
• prenatal screening available

2008; law stipulates that medical practitioners give accurate, up-to-date information about any prenatal or postnatal diagnosis received by parents and that they connect parents with appropriate support services

• XXY (Klinefelter syndrome)
• XYY
• Trisomy X (XXX)
• Monosomy X (Turners syndrome)

• Klinefelter syndrome
• 1/500-1000 male births
• testes are small; sterile
• breast enlargement and other female body characteristics
• subnormal intelligence

• 1/1000 males
• normal sexual development
• no well defined syndrome
• taller than average

• trisomy X
• 1/1000 female births
• healthy
• taller than average
• at risk for learning disabilities
• fertile

• monosomy X (Turners syndrome)
• 1/2500 female births
• only known viable monosomy in humans
• sterile
• estrogen replacement therapy will develop secondary sex characteristics
• normal intelligence

• cri du chat ("cry of the cat")
• CML

• deletion in chromosome 5
• severely intellectually disabled
• small head with unusual facial features
• cry that sounds like mewing of distressed cat "cry of the cat"
• lifespan: infancy or early childhood

• chronic myelogenous leukemia
• reciprocal translocation during mitosis of cells that will become white blood cells
• exchange of a large portion of chromosome 22 with a small fragment of time of chromosome 9
• produces a Philadelphia chromosome (shortened chromosome 22)
• causes caner by activating a gene that leads to uncontrolled cell cycle progression

variation in phenotype depending on whether an allele is inherited from the male or female parent (most imprinted genes are on autosomes)(over 60 imprinted genes have been identified, with hundreds more suspected)

• in many cases, it seems to consist of methyl (-CH₃) groups that are added to cytosine nucleotides of one of the alleles (methylation)
• methylation of certain cytosines on the paternal chromosome leads to expression of the paternal Igf2 allel, by an indirect mechanism involving chromatin condensation

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genes outside the nucleus

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1909; Discovered that extranuclear genes exist; studied the inheritance of yellow or white patches on leaves of a green plant

nervous system, muscles

1. mitochondrial myopathy
2. Leber's hereditary optic neuropathy

• mitochondrial disorder
• causes weakness, intolerance of exercise, and muscle deterioration

• mitochondrial disorder
• can produce sudden blindness in people as young as their 20's or 30's
• the four mutations found thus far to cause this disorder affect oxidative phosphorylation during cellular respiration

• some types of diabetes, heart disease, and Alzheimer's
• believed to be a part of the normal aging process