Human Genetics Exam 2

These flashcards cover key concepts in human reproductive anatomy, embryonic development, teratogens, genetic sex determination, DNA structure, and genetic disorders.

What are the primary male reproductive organs and their functions?

Testes produce sperm and hormones; epididymis stores and matures sperm; vas deferens transports sperm; accessory glands (Prostate, seminal vesicles, bulbourethral glands) secrete fluids; penis conducts sperm through the urethra.

What are the primary female reproductive organs and their functions?

Ovaries produce eggs and hormones; oviduct/fallopian tube is the site of fertilization; uterus is for fetal development; vagina is the birth canal.

What is the order of early embryonic development?

Fertilization occurs in the oviduct. The blastocyst implants into the uterine lining (endometrium) at around day 10-14.Then the trophoblast layer aids implantation and forms the placenta.

What are is the term teratogen and some examples?

Agents causing embryonic or fetal abnormalities. X-rays, viruses (HIV, rubella), certain medications, and alcohol (causing fetal alcohol syndrome).

What are the different sex determination systems seen in the animal kingdom?

XX/XY System: Males (XY) are heterogametic, females (XX) are homogametic (ex. humans).

XX/XO System: Males (XO) have one sex chromosome, females (XX) have two (ex. insects).

ZW/ZZ System: Females (ZW) are heterogametic, males (ZZ) are homogametic (ex. birds, reptiles).

Temperature-Dependent: In reptiles like alligators, sex is determined by incubation temperature

What are the three levels that define sex in humans?

Chromosomal/Genotypic sex, Gonadal sex, Phenotypic sex.

What is the significance of the SRY gene in sex determination?

The SRY gene triggers the development of testes and male internal structures.

When and how does sex differentiation in fetal development occur?

It begins in the seventh week, the SRY gene triggers testes development, Testosterone promotes male internal structures. And Anti-Müllerian Hormone (AMH) prevents female internal structures. So the absence of SRY leads to female development.

How can mutation uncouple chromosomal sex from phenotypic sex (describing the phenotype of the genetic disorders)?

Mutations in genes like the SRY gene or androgen receptor can lead to conditions such as Androgen Insensitivity Syndrome, where individuals with XY chromosomes develop female physical traits despite having male genetic coding. Gonadal Intersexuality is when an individual is chromosomally male (XY) but phenotypically female due to insufficient testosterone/DHT.

What is Lyon hypothesis and its role in dosage compensation; discuss the concept of mosaicism.

When one X chromosome is randomly inactivated in female mammals to balance gene dosage between sexes. Mosaicism is when females can express different X-linked genes in different tissues depending on which X chromosome is inactivated.

How do you calculate the number of Barr bodies in a cell?

Barr bodies = Number of X chromosomes - 1.

What differentiates sex-influenced traits from sex-limited traits?

Sex-influenced traits are expressed in both sexes but are dominant in one; sex-limited traits are only expressed in one sex despite being in both.

How does the heterogametic sex differ from the homogametic sex?

Gametes of the heterogametic sex have different sex chromosomes; gametes of the homogametic sex have the same sex chromosome

What experiments and significance does Friedrich Miescher?

Friedrich Miescher

○ Isolated nuclei discovered a substance he called "nuclein."

○ Significance: First identification of DNA, though its role was not yet understood.

What experiments and significance does Frederick Griffith?

○ Conducted experiments with pneumonia-causing bacteria in mice.

○ Found that harmless bacteria could become virulent when mixed with

heat-killed virulent bacteria.

○ Significance: Discovered the "transforming principle," suggesting genetic

material could be transferred between cells

What experiments and significance does Avery, MacLeod, and McCarty?

Avery, MacLeod, and McCarty (1944):

○ Identified DNA as the transforming factor by treating heat-killed bacteria

with enzymes that destroyed proteins, RNA, or DNA.

○ Transformation only stopped when DNA was destroyed.

○ Significance: Provided strong evidence that DNA is the genetic material

What experiments and significance does Hershey & Chase?

• Hershey and Chase:

  • Use bacteriophages (viruses that infect bacteria) to demonstrate that DNA, not protein, is the genetic material, by labeling phage DNA and protein with radioactive isotopes and tracking their fate during infection. 

  • Significance: Proved that DNA is the genetic material in viruses.

What experiments and significance of Erwin Chargaff?

Erwin Chargaff:

○ Analyzed the composition of DNA across species and found consistent

base-pairing ratios.

○ Chargaff's Rules: The amount of adenine (A) equals thymine (T), and

guanine (G) equals cytosine (C).

○ Significance: Provided the foundation for understanding base pairing in

the DNA structure

What experiments and significance does Rosalind Franklin have?

Rosalind Franklin:

○ Used X-ray diffraction to produce images of DNA fibers.

○ Her famous "Photo 51" revealed the helical structure of DNA.

○ Significance: Provided critical data that led to the discovery of the double

helix structure of DNA

What are the components of a nucleotide?

Nitrogen-containing base (purines {Adenine and Guanine} and pyrimidines{Cytosine, Thymine, and Uracil in RNA}), sugar (deoxyribose for DNA, ribose for RNA), and a phosphate group.

Describe the Watson and Crick model of DNA. Include components, bonding, base-pairing, etc

Structure:

○ Double helix with two antiparallel polynucleotide chains.

○ Sugar-phosphate backbone on the outside, bases on the inside.

● Base Pairing:

○ Adenine (A) pairs with Thymine (T) via 2 hydrogen bonds.

○ Guanine (G) pairs with Cytosine (C) via 3 hydrogen bonds.

● Significance:

○ Explains replication through complementary base pairing. Hydrogen bonds through bases

○ Provides a mechanism for genetic information storage and mutation.

Compare and contrast the structure of DNA with RNA

Both DNA and RNA are nucleic acids but differ in structure: DNA is double-stranded with a deoxyribose sugar and contains the base thymine, while RNA is single-stranded with a ribose sugar and contains uracil instead of thymine. DNA is more stable and function as genetic information storage while RNA is less stable and involved in protein synthesis, and gene regulation.

What is the mechanism of semi-conservative replication and its involved enzymes and their functions?

Def: Each new DNA molecule consists of one original strand and one newly synthesized strand.

1. Unwinding:

■ DNA helicase breaks hydrogen bonds between strands.

■ Single-strand binding proteins prevent reannealing.

■ DNA gyrase (topoisomerase) relieves supercoiling.

2. Priming:

■ Primase synthesizes short RNA primers.

3. Elongation:

■ DNA polymerase adds nucleotides in a 5′ to 3′ direction.

■ Leading strand is synthesized continuously.

■ The Lagging strand is synthesized in Okazaki fragments.

4. Joining:

■ DNA polymerase I replaces RNA primers with DNA

DNA ligase seals gaps between Okazaki fragments

Describe the organization of DNA in chromosomes and the process of compaction into the cell nucleus.

Levels of DNA Packaging:

○ DNA wraps around histone proteins to form nucleosomes ("beads on a

string").

○ Nucleosomes coil to form chromatin fibers.

○ Chromatin fibers loop and fold to form chromosomes.

Significance:

○ Allows long DNA strands to condense inside cell

○ Regulates gene expression by controlling DNA accessibility

What role do telomeres and telomerase play?

They protect chromosome ends from degradation and fusion, shortening with each cell division.

Telomerase is an enzyme that adds these sequences back, extending the lifespan of cells and maintaining genomic stability. Present in stem and cancer cells. Indicate aging and cell senescence.

Trace the flow of genetic information described in the Central Dogma, including where each step occurs within a cell.

• Transcription occurs in the nucleus, where DNA is transcribed into pre-mRNA.

• RNA processing occurs in the nucleus, turning Pre-RNA into a mature form, which then leaves the nucleus.

• Translation occurs in the cytoplasm, where ribosomes translate the mRNA into a polypeptide. The polypeptide chain is processed and folded into a functional protein.

Describe the significance of Garrod's and Beadle's & Tatum's experimental works.

Garrod (alkaptonuria): Established that genes affect metabolism by causing defective enzymes. Genes affect proteins

Beadle & Tatum (Neurospora): Showed that specific mutations in DNA cause loss of activity in a specific enzyme. Proved that genes produce phenotypes through proteins.

Describe the three steps of transcription

• Initiation: RNA polymerase binds to the promoter and unwinds DNA helix.

• Elongation: Continued unwinding of DNA, RNA polymerase reads DNA and synthesizes pre-mRNA.

• Termination: RNA polymerase reaches a stop signal, releasing the pre-mRNA, allowing DNA to reform into the double helix

Explain the functions of mRNA, tRNA, and rRNA. 

• mRNA (messenger RNA): Carries genetic instructions from DNA to ribosomes.

• tRNA (transfer RNA): Brings amino acids to the ribosome during translation.

• rRNA (ribosomal RNA): Forms ribosomes and helps catalyze protein synthesis.

Describe how pre-mRNA is processed in eukaryotes and how alternative splicing allows one gene to code for multiple polypeptides. 

In eukaryotes, pre-mRNA undergoes processing through the addition of a 5' cap, splicing to remove introns and join exons, and the addition of a 3' poly(A) tail, resulting in a mature mRNA ready for translation.

Alternative splicing allows a single gene to produce multiple proteins by splicing exons in different ways.

Diagram the structure of an amino acid. 

Consists of an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom (H), and a side chain (R group) attached to a central carbon.

Describe the three steps of translation

• Initiation: mRNA binds to the small ribosomal subunit, initiator tRNA, and a large ribosomal subunit 

• Elongation: tRNAs bring amino acids, forming a polypeptide.

• Termination: Ribosomes reach a stop codon, and the polypeptide is released.

List and describe the four levels of protein structure.

• Primary: Amino acid sequence.

• Secondary: α-helices and β-pleated sheets (formed by hydrogen bonding).

• Tertiary: 3D shape due to interactions between R groups. The folding of secondary structures

• Quaternary: Multiple polypeptides forming a functional protein.

Describe mechanisms of gene regulation that are used to control gene expression.

• Transcriptional: The addition of methyl groups to cytosine bases in DNA

• Translational: Lengthening the poly-A tail increases translation of the mRNA molecule. Shortening the poly-A-tail decreases translation of the mRNA molecule 

• Post-transcriptional: Alternative splicing, mRNA degradation.

• Post-translational: Processing, protein folding, degradation.

Describe enzymes and their functions

Enzymes speed up chemical reactions, lowering the activation energy requirement to start the metabolic reactions

What is phenylketonuria (PKU)?

An autosomal recessive disorder that affects Phenylalanine, which is the starting amino acid that starts metabolism. It causes buildup of phenylalanine and resulting in brain damage if untreated.

Identify possible phenotypic effects of genetic mutations that eliminate or alter the activity of an enzyme.

• Consequences range from no visible effects to severe disorders.

• Example: Alkaptonuria, caused by a mutation in homogentisate 1,2-dioxygenase, leads to homogentisic acid accumulation, affecting joints and urine color.

Trace the metabolic phenylalanine pathway and the genetic disorders associated with it.

• Phenylalanine is converted to tyrosine by phenylalanine hydroxylase.
  Disorders caused by mutations in this pathway include:

  • Phenylketonuria (PKU): Buildup of phenylalanine and phenyl pyruvic acid, leading to brain damage if untreated.

  • Alkaptonuria: Accumulation of homogentisic acid, affecting joints and urine color.

  • Tyrosinemia II: Defects in tyrosine metabolism.

  • Albinism: Disruptions in melanin production.

  • Genetic Goitrous Cretinism: Defective thyroid hormone production.

  • Neonatal tyrosinemia

Explain how mutations affect carbohydrate metabolism and the causes & symptoms of galactosemia and lactose intolerance.

• Mutations in carbohydrate metabolism genes can lead to disorders like:

  • Galactosemia: Mutation in the GALT gene results in toxic accumulation of galactose-1-phosphate. Symptoms include intellectual disability and blindness, managed by a low-galactose diet.

  • Lactose Intolerance: Due to decreased lactase activity, leading to digestive issues. Unlike galactosemia, it results from gene expression variation rather than a mutation.

What are pharmacogenetics and pharmacogenomics?

Pharmacogenetics studies genetic variations in individual drug responses; pharmacogenomics focuses on drug development tailored to genetic makeup.