Human Biology: Quiz #3
Autosomal and sex-chromosome disorders resulting from nondisjunction
- "Trisomy" having three chromosomes of one type (Trisomy 21- Down Syndrome, Trisomy 18- Edwards Syndrome, Trisomy 13- Patau Syndrome) - XYY- Jacob Syndrome - XXY-Klinefelter syndrome - XXX- Trisomy-X syndrome - XO- Turner Syndrome
What is the possible number of combinations of genetic information, accounting for independent assortment and random fertilization?
- 64 trillion - 8 million possible combinations from each sperm and each egg, so 64 trillion combinations for zygote
The number of possible chromosome combinations in a human gamete, considering independent assortment but not crossing over, is about...
- 8 million
Which of the following DNA mutations is the most likely to be damaging to the protein it specifies?
- A base-pair deletion
The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in...
- A polypeptide missing an amino acid
Which of the following would provide the most accurate prediction of ovulation?
- A surge in LH
The nitrogenous base adenine is found in all members of which group?
- ATP, RNA, & DNA
The shared genetic code of all life on Earth is evidence that ________.
- All life shares a common ancestry
Genetic code
- All possible 3 letter combinations of A U C and G and the amino acids they designate - Universal and redundant
Peptide bonds form between ________.
- Amino acids
What does "transfer RNA" actually transfer?
- Amino acids
Deletions
- An altered chromosome structure resulting from the loss of part of the chromosome
The sex hormones secreted in greater amounts by males than by females are the...
- Androgens
Where are LH and FSH produced?
- Anterior pituitary gland
Secondary sex characteristics are traits that...
- Are not directly related to fertility
Testosterone functions inside a cell by...
- Binding with a receptor protein that enters the nucleus and activates specific genes
Alternative RNA splicing....
- Can allow the production of proteins of different sizes from a single mRNA
RNA processing
- Cap" and "tail" added - Introns removed - Exons "spliced" together - Mature mRNA ready for translation
Describe the process of how transcription factors are activated
- Cell communication occurs through molecular cell signaling (internal or external cues) - Cascade/domino effect/transduction pathway: signal --> activation of a transcription factor --> gene expression (transcription/translation) - Signal molecule secreted and enters cell membrane, received by receptor protein in cell, moves through signal transduction pathway to target cell, transcription factor activated, nucleus responds by beginning process of making protein
What are hormones?
- Chemicals transported in the blood that affect target cells throughout the body
Where are estrogen and progesterone produced?
- Corpus luteum of ovaries
An allele on the paternal chromosome 18 ends up on the maternal chromosome 18. Is this random fertilization, crossing over, or independent assortment?
- Crossing over (The exchange of DNA between paired homologous chromosomes that occurs during meiosis)
Process of Transcription
- DNA is copied into mRNA (Transfers information from DNA into mRNA; RNA is synthesized)
In comparing DNA replication with RNA transcription in the same cell, which of the following is true only of replication?
- DNA replication has the entire template molecule represented in the product
Which disorders are autosomal disorders?
- Down Syndrome, Edwards Syndrome, Patau Syndrome
Random fertilization
- Each gamete contains a different combination of genetic information that can potentially combine with another gamete containing any combination of information - Random chance that each sperm and egg will unite
A frameshift mutation could result from...
- Either an insertion or a deletion of a base
Both the _____ system + _____ system are controlled by negative feedback.
- Endocrine - Nervous
The expressed (coding) regions of eukaryotic genes are called ________.
- Exons
Introns vs. Exons
- Exons contain the actual genetic information coding for protein - Introns are intervening noncoding segments of DNA. ("INtrons stay IN the nucleus, whereas exons are EXpressed)
Which 2 hormones are gonadotropins? What (very generally) do they do?
- FSH and LH - Regulate the gonads (testes and ovaries) - FSH stimulates gamete production and LH stimulates production of hormones by gonads
Non-disjunction
- Failure of chromosomes to separate properly during meiosis, likely due to a failure in the spindle apparatus - Effects more severe in meiosis I because every gamete will be abnormal (some of the gametes will have one extra chromosome and some will have too few) - In meiosis II, some of the gametes will be N+1 or N-1, but the other half will be normal
What would occur if testosterone & inhibin levels dropped below normal?
- Fewer sperm produced - Negative feedback relaxed - More GnRH, LH and FSH released
If a male produced lower than normal levels of FSH, what effect would you predict?
- Fewer sperm would be formed
Independent assortment
- Freedom for each homologous pair to align independently of how the other pair aligns - Genes on different chromosomes assort independently - For any pair of chromosomes, 2 possibilities for orientation, so variation exponentially increases
Secretion of hormones by the anterior pituitary gland is closely regulated by the...
- Hypothalamus
Function of hypothalamus, pituitary gland, and the hormones
- Hypothalamus and pituitary gland- "master" regulators, producing hormones that cascade down to the gonads, which in turn produce their own hormones for regulation through negative feedback loop - Hypothalamus produces releasing and inhibiting hormones, including GnRH - Anterior pituitary produces FSH and LH - FSH and LH target specialized cells in the gonads, which produce estrogen/progesterone and testosterone
What maximizes the chances of crossing over?
- If the genes are farther apart on the chromosomes
Why does nondisjunction have more severe consequences in meiosis than mitosis?
- In mitosis, the two daughter cells often die - In meiosis, alterations have potential to disrupt the development of an entire organism and its offspring for generations; this mutation will be in every single cell in the offsprings' DNA.
Random combinations of paternal and maternal chromosomes end up in gametes. Is this random fertilization, crossing over, or independent assortment?
- Independent assortment (Alleles get separated into gametes independently of one another)
The CORRECT sequence of events that occurs during transcription is ________.
- Initiation, elongation, termination
Where does transcription take place?
- Inside the nucleus
How does a zygote first know to begin making proteins?
- Internal cues (including transcription factors and other molecules) that originated in the mother signal the zygote to begin making proteins - Signaling pathway until final activation, which activates transcription factors to instruct what genes need to be expressed
What is the role of the corpus luteum during early pregnancy?
- It produces the hormones that support the early pregnancy
Which disorders are related to the sex chromosomes?
- Klinefelter (XXY) - Jacob (XYY) - Trisomy X-chromosome (XXX) - Turner (XO)
The hormone _________ stimulates the _________ to produce testosterone.
- LH - Interstitial Cells
Target cells for LH and FSH in males and females
- LH in males - interstitial cells (which produce testosterone) - FSH in males - (sertoli cells) - FSH and LH in females - granulosa cells of the follicle (in the ovaries)
Seminiferous tubules
- Location in the testes where sperm are produced - Walls made up of developing sperm cells (least developed at the periphery and the fully developed sperm in the lumen/ center opening) - Developing spermatocytes surrounded by "nurse" Sertoli cells, which protect germ cells and promote development - Other cells between walls of tubules are the interstitial cells, which produce high levels of testosterone
Transcription is the ________.
- Manufacture of a strand of RNA complementary to a strand of DNA
The RNA that is translated into a polypeptide is ________ RNA.
- Messenger
Is the coding and template strand always the same for all genes?
- No, some genes are transcribed using one DNA strand as a template, while others are transcribed using the other DNA strand
Which two hormones most directly regulate lactation?
- Oxytocin + prolactin
Parental vs recombinant chromosomes
- Parental = the sister chromatid that does not engage in crossing over, providing for parental type - Recombinant- the sister chromatid that undergoes crossing over
Inhibin
- Produced by Sertoli cells, works w testosterone to inhibit the secretion of FSH, LH, and GnRH (functioning on negative feedback loop)
What indicates where transcription starts?
- Promoter
_____________ sequence indicates where transcription starts.
- Promoter
What signals the start of a gene and where transcription begins?
- Promoter sequence
GnRH (gonadotropin-releasing hormone)...
- Promotes secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Transcription factors
- Proteins that regulate gene expression - Tell the zygote which genes to turn on to start dividing
Translation converts the information stored in ________ to ________.
- RNA - Polypeptide
_____________ does the work (is an enzyme) of transcription.
- RNA polymerase
RNA structure vs DNA structure
- RNA: single stranded, ribose, uracil (U) - DNA: double stranded, deoxyribose, thymine (T)
The formation of a zygote from an egg and a sperm is an unpredictable event. Is this random fertilization, crossing over, or independent assortment?
- Random fertilization (Hence, unpredictable)
Sources of genetic variation in meiosis & sexual reproduction
- Random fertilization - Independent assortment - Crossing over
A and B are linked genes. In a study of 100 offspring, 94 had parental combinations of A and B, while only 6 were recombinants. Based on this information, you can conclude that genes A and B are...
- Relatively close together on the same chromosome
Which of the following is a way in which replication and transcription differ?
- Replication copies both strands of a DNA molecule - Transcription copies only a segment of one strand of the DNA molecule
A mutation within a gene that will insert a premature stop codon in mRNA would ________.
- Result in a shortened polypeptide chain
What cellular structure facilitates the process of translation?
- Ribosomes
Where does translation take place?
- Ribosomes in the cytoplasm
Mechanical support and protection for developing germ cells in the testis are provided by...
- Sertoli cells
If a strand of DNA has the sequence GACTTA, transcription will result in a(n) ________.
- Single RNA strand with the sequence CUGAAU
Start codon and stop codon key difference
- Start codon always codes for methionine -Stop codon has no amino acid is associated with it
Excessive levels of estrogen __________ a surge of LH to prompt __________.
- Stimulate - Ovulation
Crossing over
- Swapping genes from one homologous chromosome to the other - Recombination, making gametes more genetically unique - Separates linked genes/alleles
What indicates where transcription stops?
- Terminator
Imagine that you have cultured a mutant cell line that contains histones resistant to acetylation. Based on this information only, what phenotype could you confidently predict for this cell line?
- The cell line will show low levels of gene expression (Acetylation = epigenetic change = impact on gene expression)
Which is likely to be the shortest chain of nucleotides?
- The mRNA
How many nucleotides make up a codon?
- Three
DNA contains the nitrogenous base ________ instead of ________, which is found only in RNA.
- Thymine - Uracil
Complex of __________________ and other control sequences direct RNA polymerase to the promoter (turns gene ON).
- Transcription factors
How is RNA polymerase guided to promoter?
- Transcription factors
Transcription in eukaryotes requires which of the following in addition to RNA polymerase?
- Transcription factors
The transfer of information from RNA into a protein is known as ________.
- Translation
Which of the following statements is true about protein synthesis in prokaryotes?
- Translation can begin while transcription is still in progress
Pieces of chromosomes exchanged between nonhomologous chromosomes is called _____.
- Translocation (Occurs when a chromosome breaks and the fragmented pieces re-attach to different chromosomes)
What generally causes the specialization of cells?
- Turning different genes on and off, which is caused by transcription factors
How does structure relate to function of tRNA?
- Twisted in a way to expose an amino attachment site and an anticodon, so one end holds amino acid and one end is anticodon matching mRNA
Difference between linked and unlinked genes
- Unlinked = genes on different chromosomes - Linked = set of genes at different loci on the same chromosome, would be inherited together except for crossing over
Embryonic stem cells
- Unspecialized cells with the potential to become any cell type - Early in development, begin expressing specific genes to start differentiation
Alternative Splicing
- Used when we have too few genes for the number of proteins present - Exons from the same gene are joined in different combinations, leading to different but related mRNA transcripts - Increases diversity all exons can be spliced together in various arrangements
When can DNA not be read (transcribed)?
- When it's tightly packed.
Aneuploidy
- Zygote has abnormal number of chromsomes
Which is the most current description of a gene?
- a DNA sequence that is expressed to form a functional product: either RNA or polypeptide
_______ contains codons and _______ contains anticodons.
- mRNA - tRNA
A triplet base sequence on the coding strand of DNA reads ATT. What will be the corresponding mRNA codon and tRNA anticodon called for by this DNA?
- mRNA codon: AUU - tRNA anticodon: UUA
Template vs coding strand
- mRNA is complementary to template strand of DNA (what is read to create the RNA) - mRNA matches the coding strand of DNA (but U instead of T)
Translation requires ________.
- mRNA, tRNA, and rRNA
How doe tRNA know where to start translation?
- searches for start codon (AUG)
Role of testosterone and estrogen
- testosterone: spermatogenesis, male secondary sex characteristics - estrogen: folliculogenesis, female secondary sex characteristics
2 main functions of DNA
1) Replication (using complementary base pairing 2) Express genes that specify traits of an individual (through transcription and translation). DNA directs the production of RNA, which controls the manufacture of proteins
What are the stages of embryonic development? (Place these in order)
1. Cleavage 2. Growth 3. Differentiation 4. Morphogenesis
Meiosis promotes genetic variation through...
1. Independent Assortment 2. Crossing Over 3. Random Fertilization
Estrogen + Progesterone Function
1. Stimulates development of secondary female sex characteristics 2. Helps regulate ovarian & uterine cycles 3. Stimulates growth of female reproductive organs 4. Necessary for egg maturation
Testosterone Function
1. Stimulates secondary sex characteristics (muscle development, accessory glands) 2. Maintains libido 3. Maintain function of male reproductive tract (penis and muscles for ejaculation)
Which of the following lists the female reproductive structures that sperm will pass through on their way to fertilize an oocyte, in the correct order?
1. Vagina 2. Cervix 3. Uterus 4. Oviduct
What DNA sequence coded for this mRNA? AUG-ACU-AAA-GAG-UCA-UAA
ATG-ACT-AAA-GAG-TCA-TAA (Coded = replace U with T)
Insertions vs. Deletions
Insertions: additions of nucleotide pairs in a gene Deletions: losses of nucleotide pairs in a gene
Epigenetic factors (importance + examples)
Play a role in whether genes are expressed or not. - DNA methylation - Acetyl groups (attaching to histones) - Chromatin remodeling
Recombination vs. Translocation
Recombination: when genetic material is exchanged between two homologous chromosomes Translocation: when genetic material is exchanged between nonhomologous chromosomes (occurs when a piece of a chromosome breaks off but attaches to another site). Results in subtle changes in gene expression and ability to function.
What DNA sequence is the template for this mRNA? AUG-ACU-AAA-GAG-UCA-UAA
TAC-TGA-TTT-CTC-AGT-ATT (A-T, C-G, U-A)
