chapter 15 the chromosomal basis of inheritance Flashcards
What did Morgan demonstrate about Mendelian inheritance?
Mendelian inheritance has its physical basis in the behaviour of chromosomes
Morgan’s work showed the correlation between genes and chromosome behaviour.
What are sex linked genes?
Genes located on sex chromosomes, such as X-linked or Y-linked genes
They exhibit unique patterns of inheritance.
Why do linked genes tend to be inherited together?
They are located near each other on the same chromosome
This proximity increases the likelihood of being passed on together.
What can alterations of chromosome number or structure cause?
Genetic disorders
These alterations can lead to spontaneous abortions or developmental disorders.
What is the significance of tagging isolated chromosomes with a fluorescent dye?
It allows for the location of genes along chromosomes to be visualized
This technique aids in genetic mapping.
What was the result of Morgan’s experiment with fruit flies regarding eye color?
The F1 generation all had red eyes, while the F2 generation showed a 3:1 ratio of red to white eyes, with only males having white eyes
This led to the conclusion that the white-eyed allele was on the X chromosome.
How are Y-linked genes inherited?
Passed only from father to son
This is due to only males having a Y chromosome.
What is required for a recessive X-linked trait to be expressed in females?
Two copies of the allele (homozygous)
Males need only one copy (hemizygous).
What are examples of X-linked recessive disorders?
- Red-green color blindness
- Hemophilia
These disorders are more common in males than females.
What is X inactivation in female mammals?
One of the two X chromosomes in each cell is randomly inactivated during embryonic development
This leads to females being mosaics for certain traits.
What is nondisjunction?
The failure of homologous chromosomes to separate normally during meiosis
This can lead to gametes with abnormal chromosome numbers.
What is aneuploidy?
An abnormal number of a particular chromosome in offspring
Results from fertilization of gametes where nondisjunction occurred.
What are the types of chromosomal alterations?
- Deletion
- Duplication
- Inversion
- Translocation
These structural changes can lead to genetic disorders.
What is Down syndrome caused by?
Three copies of chromosome 21 (trisomy 21)
This condition affects 1 in 700 children born in the US.
What is Klinefelter syndrome?
A condition resulting from an XXY chromosome configuration in males
This often leads to sterility and subtle symptoms.
What is Cri du chat syndrome?
A disorder caused by a specific deletion in chromosome 5
Individuals typically exhibit mental retardation and a characteristic cat-like cry.
What is the role of crossing over in genetic recombination?
It occasionally breaks the physical connection between linked genes on the same chromosome
This results in new combinations of alleles.
What is a linkage map?
A genetic map of a chromosome based on recombination frequencies
It helps illustrate the distances between genes.
What is polyploidy?
An organism with more than two complete sets of chromosomes
Common in plants but rare in animals.
What are the symptoms of Edwards Syndrome?
Severe disability, with babies usually not living longer than a week due to trisomy 18
This condition is less common than Down syndrome but more severe.
What is hypertrichosis?
A condition characterized by an abnormal amount of hair
It can be congenital or acquired.
True or False: Female mammals can exhibit a mosaic phenotype due to X inactivation.
True
Heterozygous females can express different traits from their X chromosomes.
How can a gene’s location be identified?
By tagging isolated chromosomes with a fluorescent dye
What accounts for Mendel’s laws of segregation and independent assortment?
The behavior of chromosomes during meiosis
Who provided the first solid evidence associating a specific gene with a specific chromosome?
Thomas Hunt Morgan
What organism did Thomas Hunt Morgan use for his experiments?
Fruit flies
What are traits alternative to the wild type called?
Mutant phenotypes
What was the F1 generation’s eye color when Morgan mated male flies with white eyes and female flies with red eyes?
All had red eyes
What ratio was observed in the F2 generation of Morgan’s fruit fly experiment?
3:1 red:white eye ratio
On which chromosome is the white-eye mutant allele located?
X chromosome
What is the main function of the Y chromosome?
Sex determination
How many genes does the Y chromosome approximately have?
About 200
Y-linked traits are passed from _______ to _______.
Father to son
What is hypertrichosis pinnae auras commonly known as?
Hairy ears
For a recessive X-linked trait to be expressed, how many copies of the allele does a female need?
Two copies (homozygous)
For a recessive X-linked trait to be expressed, how many copies of the allele does a male need?
One copy (hemizygous)
What condition is characterized by impaired blood clotting?
Haemophilia
What is the genetic cause of haemophilia?
X chromosome disorders
What is the main cause of aneuploidy?
Nondisjunction during meiosis
What is a monosomic zygote?
Has only one copy of a particular chromosome
What are the four types of changes in chromosome structure caused by breakage?
- Deletion
- Duplication
- Inversion
- Translocation
What is the mutation that causes Huntington’s disease?
Duplicate of repeat sequence in the gene coding for glutamate residues in the Huntingtin protein
Which syndrome is caused by a translocation between chromosomes 9 and 22?
Chronic Myelogenous Leukemia (CML)
What is the inheritance pattern for X-linked traits?
Males inherit one allele from their mother, and females inherit two alleles
What is the outcome if a color-blind father has daughters?
All daughters will inherit the mutant allele
What is the chance that a daughter of a carrier mother and a normal vision father will be a carrier?
50%
What is the only known variable monosomy in humans?
Turner syndrome (X0)
What is the effect of temperature on sex determination?
Determines the sex of offspring in some reptiles and teleost fish
What is the significance of X inactivation in female mammals?
One of the two X chromosomes is randomly inactivated
What is the inheritance pattern of traits on linked genes?
They tend to be inherited together
What is the flow of genetic information?
The information in DNA is in the form of specific nucleotide sequences that encode for RNA, leading to protein synthesis and specific traits
Proteins link genotype and phenotype
What are the two stages of gene expression?
Transcription and translation
Gene expression is the process by which DNA directs protein synthesis through RNA
Define transcription.
Synthesis of RNA under the direction of DNA
Messenger RNA (mRNA) is synthesized during transcription
Define translation.
Synthesis of a protein under the direction of mRNA
Ribosomes translate the mRNA into proteins
What is the template strand?
One of the two DNA strands that provides a template for mRNA synthesis during transcription
The other strand is the coding strand
What are codons?
Base triplets on mRNA that are read during translation
Codons specify the amino acids to be placed along a polypeptide
How many amino acids are there and how many nucleotide bases are in DNA and mRNA?
20 amino acids and 4 nucleotide bases
There are 64 codons, with 61 coding for amino acids and 3 as stop signals
What does AUG encode for?
Methionine and it often represents the start signal for ribosomes
AUG is one of the 64 codons
True or False: The genetic code is ambiguous.
False
The genetic code is redundant but not ambiguous
What are the three stages of transcription?
Initiation, elongation, termination
What catalyzes RNA synthesis?
RNA polymerase
It pries DNA strands apart and hooks RNA nucleotides together
What is a promoter?
The DNA sequence where RNA polymerase attaches
Promoters signal the transcriptional start point
What is the TATA box?
A promoter sequence crucial in forming the initiation complex in eukaryotes
What happens during the elongation stage of transcription?
RNA polymerase moves along the DNA, untwisting the double helix and adding nucleotides to the growing RNA molecule
Transcription progresses at a rate of 40 nucleotides per second in eukaryotes
How does termination differ between bacteria and eukaryotes?
Bacteria: RNA polymerase stops at the terminator. Eukaryotes: RNA polymerase transcribes the polyadenylation signal and the RNA transcript is released after
What are introns?
Long noncoding stretches that lie between coding regions in eukaryotic genes
They are removed during RNA splicing
What are exons?
Regions that typically encode for a protein
Exons are joined together during RNA splicing
What is alternative RNA splicing?
A process where some genes can encode more than one protein product depending on which segments are treated as introns/exons
What is the role of tRNA in translation?
Transfers amino acids to the growing protein in a ribosome
What is the structure of tRNA?
A single RNA strand about 80 nucleotides long with a specific amino acid on one end and an anticodon on the other end
What are the two steps required for accurate translation?
- Correct match between tRNA and amino acid 2. Correct match between tRNA anticodon and mRNA codon
What is wobble in tRNA pairing?
Flexible pairing at the third base of a codon that allows some tRNAs to bind to more than one codon
What are the three binding sites of a ribosome?
P site, A site, E site
P site holds the growing chain, A site holds the next amino acid, E site is the exit site
What are the three stages of translation?
Initiation, elongation, termination
What initiates translation?
The small ribosomal subunit binds with mRNA and the initiator tRNA, then moves to the start codon (AUG)
What occurs during termination of translation?
A stop codon reaches the A site, and a release factor causes the addition of a water molecule, releasing the protein
What is required for a protein to become functional after translation?
Folding into three-dimensional shapes and often undergoing post-translational modifications
What is tri-arabinose synthesis?
Complex chemistry to generate the tri-arabinose building block
Involves unique B-1,2 linkage of arabinose sugars
What are biotechnology tools?
Molecular techniques that are often universal and powerful for understanding signaling pathways and molecular-genetic interactions.
What does PCR stand for?
Polymerase chain reaction.
What is PCR used for?
To amplify DNA and determine presence/absence, generate large volumes of a target sequence, or confirm sequence presence in a sample.
What technique does PCR use?
Thermal cycling.
What is cDNA?
Complementary DNA that is very stable and represents the coding sequence of a gene without introns.
What is the stability comparison between cDNA and mRNA?
cDNA is very stable, whereas mRNA is generally not stable.
What is real-time PCR used for?
To determine transcript abundance, often referred to as gene expression.
How does real-time PCR differ from traditional PCR?
It combines amplification and detection and is slightly more expensive.
What is next-generation sequencing (NGS)?
A method used to sequence genomes or for RNA sequencing (RNAseq), known for its ultra-high throughput, speed, and scalability.
What is a significant application of RNA sequencing?
To identify genes that are differentially regulated in expression.
What is gene cloning?
A widely used method that amplifies a sequence of interest, which can be stored as a plasmid or in bacteria.
What can gene cloning be used for?
To transform another organism or produce products of interest.
What is transformation in the context of genetic engineering?
The process of overexpression, often involving promoter::reporter fusions and CRISPR.
What is bioinformatics?
The use of programs and tools to identify genes, genome structures, introns, promoter regions, and visualize gene expression profiles.
What do gene atlases enable?
The visualization of gene expression patterns in various tissues.
Fill in the blank: PCR is a _______ method.
widely used.
True or False: cDNA includes introns.
False.
What is one challenge in gene cloning?
Difficulty can be in the species or variety being transformed.
What is the main focus of next-gen sequencing?
To sequence genomes or perform RNA sequencing.
