Chapter 15 Memorization
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89 Terms
What is the chromosomal theory of inheritance?
Genes are located on chromosomes, and chromosome behavior during meiosis explains Mendel's laws.
Who proposed the chromosomal theory of inheritance?
Sutton and Boveri.
What does the chromosomal theory explain about segregation?
Homologous chromosomes separate during meiosis.
What does the chromosomal theory explain about independent assortment?
Different homologous pairs align independently in meiosis I.
What happens to chromosome number during meiosis?
It is reduced by half in gametes.
What happens to chromosome number during fertilization?
Diploidy is restored.
Who provided early evidence that genes are located on specific chromosomes?
Thomas Hunt Morgan.
What organism did Thomas Hunt Morgan study?
Drosophila melanogaster, the fruit fly.
Why were fruit flies useful for Morgan's experiments?
They produce many offspring, reproduce quickly, and have only four chromosome pairs.
What is the wild type?
The common phenotype found in natural populations.
What is a mutant phenotype?
A phenotype that differs from the wild type.
What was the wild-type eye color in Morgan's fruit flies?
Red.
What was Morgan's first mutant eye-color phenotype?
White eyes.
Where was Morgan's white-eye allele located?
On the X chromosome.
What did Morgan's white-eye experiment support?
The chromosome theory of inheritance.
What are sex chromosomes?
Chromosomes that determine sex in many organisms.
What are autosomes?
Chromosomes other than sex chromosomes.
What sex chromosomes do typical human females have?
XX.
What sex chromosomes do typical human males have?
XY.
Which human sex chromosome is larger and contains more genes?
The X chromosome.
Which human sex chromosome is smaller and contains fewer genes?
The Y chromosome.
What regions allow X and Y chromosomes to pair in male meiosis?
Small homologous regions at their ends.
What is the SRY gene?
A Y-linked gene that triggers testis development.
Where is the SRY gene located?
On the Y chromosome.
What is the X-Y sex-determination system?
Females are XX and males are XY.
What is the X-0 sex-determination system?
Females have two X chromosomes and males have one X chromosome.
What is the Z-W sex-determination system?
Females are ZW and males are ZZ.
What is the haplo-diploid sex-determination system?
Females are diploid and males are haploid.
What is a sex-linked gene?
A gene located on a sex chromosome.
What does X-linked usually mean in humans?
Located on the X region without a matching Y region.
Why are X-linked recessive disorders more common in males?
Males have only one X-linked allele.
What does hemizygous mean?
Having only one copy of a gene instead of a pair.
What is an example of an X-linked recessive disorder?
Color blindness.
What is another X-linked recessive disorder?
Duchenne muscular dystrophy.
What is another X-linked recessive disorder involving clotting?
Hemophilia.
What does red-green color blindness affect?
Distinguishing red from green colors.
What does Duchenne muscular dystrophy cause?
Progressive muscle weakness and degeneration.
What does hemophilia cause?
Impaired blood clotting.
What is X inactivation?
Random inactivation of one X chromosome in female mammal cells.
When does X inactivation occur?
Early in embryonic development.
What is a Barr body?
A condensed, inactive X chromosome.
Why do female mammals form Barr bodies?
To equalize X-linked gene dosage with males.
What is a mosaic?
An individual with genetically different cell populations for a trait.
Why can a heterozygous female be a mosaic for an X-linked trait?
Different cells inactivate different X chromosomes.
Why are calico cats usually female?
Their coat-color genes are X-linked and X inactivation creates patches.
What are linked genes?
Genes close together on the same chromosome.
Do tightly linked genes assort independently?
Usually no.
What are parental types?
Offspring with the same trait combinations as the parents.
What are recombinant types?
Offspring with trait combinations different from either parent.
What is genetic recombination?
Production of new allele combinations.
What produces recombinants from linked genes?
Crossing over between homologous chromosomes.
When does crossing over occur?
During prophase I of meiosis.
What is recombination frequency?
The percentage of recombinant offspring.
What recombination frequency is expected for unlinked genes?
About 50%.
What does a recombination frequency below 50% suggest?
The genes are linked.
What is a linkage map?
A genetic map based on recombination frequencies.
What is a map unit?
A unit of genetic distance equal to 1% recombination frequency.
What is another name for a map unit?
A centimorgan.
What do map units show?
Relative gene distance and order.
Do map units show exact physical DNA distance?
No.
What is nondisjunction?
Failure of chromosomes or sister chromatids to separate normally.
What is aneuploidy?
An abnormal number of a particular chromosome.
What is a monosomic zygote?
A zygote with one copy of a chromosome.
What is a trisomic zygote?
A zygote with three copies of a chromosome.
What is polyploidy?
Having more than two complete chromosome sets.
What is triploidy?
Having three complete chromosome sets.
What is tetraploidy?
Having four complete chromosome sets.
In which organisms is polyploidy more common?
Plants.
What is a deletion?
Loss of a chromosome segment.
What is a duplication?
Repetition of a chromosome segment.
What is an inversion?
Reversal of a chromosome segment's orientation.
What is a translocation?
Movement of a chromosome segment to another chromosome.
What is Down syndrome?
Trisomy 21.
What chromosome change causes Down syndrome?
Three copies of chromosome 21.
What is Klinefelter syndrome?
An XXY chromosome condition in a male.
What is Turner syndrome?
A monosomy X condition, written X0.
What is the only viable human monosomy commonly described?
Turner syndrome.
What is cri du chat syndrome caused by?
A deletion on chromosome 5.
What does cri du chat mean?
Cry of the cat.
What chromosome change is associated with chronic myelogenous leukemia?
A translocation.
What are extranuclear genes?
Genes located outside the nucleus in organelles.
Which organelles contain extranuclear DNA?
Mitochondria and chloroplasts.
Why are organelle genes usually inherited maternally?
The zygote receives most cytoplasm from the egg.
What type of DNA is inherited only from the mother in typical human inheritance?
Mitochondrial DNA.
What can mitochondrial gene defects reduce?
ATP production.
What body systems are commonly affected by mitochondrial disorders?
Muscular and nervous systems.
What is genomic imprinting?
Parent-specific gene expression caused by silencing one parental allele.
What determines the phenotype in genomic imprinting?
Which parent contributed the allele.
How does genomic imprinting differ from ordinary dominance?
Expression depends on parent of origin rather than allele dominance alone.