Biology 1 Chapter 15 (Lecture) Flashcards
The reason that linked genes are inherited together is that
They are located on the same chromosome
What is the mechanism for the production of genetic recombinants?
Crossing over and independent assortment
Males are more often affected by sex-linked traits than females because
Males are hemizygous for the X chromosome
A man who carries an X-linked allele will pass it on to
All of his daughters
What syndrome afflicts mostly males?
Duchenne Muscular Dystrophy
If a chromosome lacks certain genes, what has most likely occurred?
A deletion
Of the Human trisomies, the one that generally has the most severe impact on the health of the individual is
Trisomy 21
What do all human males inherit from their mother?
An X chromosome and mitochondria DNA
What is false about Down’s Syndrome?
It is a sex-linked disorder
What is not true of Turner’s Syndrome?
They are genetically XXX
What results in male sex organs but may have some female body characteristics present? (They are also sterile and may have subnormal intelligence)
XXY
What is not a sex-linked disorder?
Sickle Cell Anemia
What kind of chemical bond is found between paired bases of the DNA double helix?
Hydrogen
In an analysis of the nucleotide composition of DNA, what is true?
A+C=G+T and G+A=T+C
The strands that make up DNA are antiparallel. This means that
The 5’ to 3’ direction of one strand runs counter to the 5’ to 3’ direction of the other strand
What is the function of DNA polymerase?
To add nucleotides to the end of a growimng DNA strand
Removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3’ end of Okazaki fragments
DNA polymerase I
Separates the DNA strands during replication
Helicase
Covalently connects segments of DNA
Ligase
Synthesizes short segments of RNA
Primase
Wild Type
The phenotype for a character most commonly observed in natural populations
Mutant Phenotypes
Traits that are alternatives to the wild type.
Because they are due to alleles assumed to have originated as changes or mutations in the wild type allele.
Sex-Linked Gene
A gene located on either sex chromosome
Fathers pass sex-linked alleles to all of their…
Daughters but none to their sons.
Mothers can pass sex-linked alleles to…
Sons and Daughters
Far more _____ have sex-linked recessive disorders
Males
Male sex-linked recessive disorders
- Color Blindness
- Duchenne Muscular Dystrophy
- Hemophilia
Duchenne Muscular Dystrophy
- 1/3500 males born in US
- Progressive weakening of the muscles and loss of coordination
- Rarely live past early 20’s
- Absence of a key muscle protein (dystrophin) and have mapped the gene for this protein to specific locus on the x chromosome
Hemophilia
Defined by the absence of one or more of the proteins required for blood clotting
- Bleeding is prolonged because firm clot is slow to form
- Small cuts are usually ok; but bleeding in the muscles or joints can be painful and can lead to serious damage
- Treated as needed with IV injections of the missing proteins.
Barr Body
The inactive X in each cell of a female condenses into a compact object.
Most of these genes are not expressed. Females are a mosaic of two types of cells: those with active X derived from the father and those with active X derived from the mother.
Linked Genes
Genes located on the same chromosome that tend to be inherited together in genetic crosses.
Genetic Recombination
Offspring that inherit a phenotype that is different from either parent
If there is a 50% frequency of recombination in a heterozygous x homozygous testcross tells us…
That the two genes are located on different chromosomes and are thus unlinked.
Crossing Over
Accounts for the recombination of linked genes. In this end portions of two nonsister chromatids trade places each time a crossover occurs.
Genetic Map
An ordered list of the genetic loci along a particular chromosome.
The farther apart two genes are, the higher the probability that…
A crossover will occur between them and therefore the higher the recombination frequency.
Linkage Map
A genetic map based on recombination frequencies
Nondisjunction
A mishap in which the members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosisII. In these cases, one gamete receives 2 of the same type of chromosome and the other receives 0 copies.
Aneuploidy
If this aberrant gamete unites with a normal on at fertilization the zygote will have an abnormal number of chromosomes.
Alterations of chromosome structure due to chromosome breakage:
- Deletion
- Duplication
- Inversion
- Translocation
Deletion
Chromosomal fragment is lost
Duplication
When an extra segment is attached to a sister chromatid
Inversion
reverses a segment within the chromosome
Translocation
Moves a segment from one chromosome to a nonhomologous chromosome
Genes located in organelles in the cytoplasm contain small circular DNA molecules
- Mitochondria
- Chloroplasts
- Plant Plastids
Almost all mitochondrial DNA is…
Maternal DNA almost all the mitochodria passed on to the zygote comes from the cytoplasm of the egg (Instead of the sperm)
