Genetics Overview and Mutation Types

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Questions and Answers

What type of mutation results from the insertion or deletion of base pairs in a way that affects the reading frame?

Missense mutation

Frameshift mutation (correct)

Silent mutation

Nonsense mutation

Which of the following correctly defines a heterozygous organism at a given locus?

A single allele present

All alleles are recessive

Two different alleles (correct)

Two identical alleles

What does incomplete penetrance refer to in genetics?

All individuals express the phenotype variably

Phenotype expression is always identical

All individuals with a genotype show the phenotype

Some individuals with a genotype do not express the phenotype (correct)

What type of genetic change involves only a single base pair substitution?

Base pair substitution Signup and view all the answers

Which of the following is a characteristic of somatic cells?

Are diploid with 46 chromosomes Signup and view all the answers

Which element is not part of the nitrogenous bases found in DNA?

Uracil Signup and view all the answers

What type of agents increase the frequency of mutations and can affect fetal development post-implantation?

Mutagens Signup and view all the answers

How many base pairs are always present in a codon?

3 base pairs Signup and view all the answers

What is the recurrence risk for an individual developing an autosomal recessive genetic disease when one parent is affected and the other is a carrier?

25% Signup and view all the answers

In X-linked inheritance, which statement is true regarding the offspring of a male affected by an X-linked disorder?

His daughters will be carriers. Signup and view all the answers

What chromosomal abnormality is characterized by having one less chromosome than the normal diploid number?

Aneuploidy Signup and view all the answers

Which of the following statements regarding multifactorial inheritance is correct?

It has a specific threshold of liability. Signup and view all the answers

What is the result of nondisjunction during meiosis?

Aneuploidy. Signup and view all the answers

What type of genetic condition tends to skip generations and typically requires both parents to be carriers?

Autosomal recessive disorder Signup and view all the answers

Which of the following accurately describes a characteristic of chromosomal aberrations?

All euploid cells have a normal number of chromosomes. Signup and view all the answers

What is the primary role of microRNAs (miRNAs) in cellular functions?

To modulate stability and translational efficiency of mRNA. Signup and view all the answers

What term describes the state when euploid cells contain more than the diploid number of chromosomes?

Polyploidy Signup and view all the answers

What is characterized by developmental delays, cognitive deficits, and facial abnormalities?

Cri-du-chat syndrome Signup and view all the answers

Study Notes

Embryonic Stem Cells

Totipotent: Capable of differentiating into any type of cell.

Somatic Cells

46 chromosomes
Diploid
Mitosis

Gametes

23 chromosomes
Haploid
Meiosis

DNA Structure

4 nitrogenous bases: Adenosine, Guanine, Cytosine, Thymine
Adenosine and Guanine – Purines
Cytosine and Thymine – Pyrimidines
Phosphate molecule
Double helix
Always has 3 base pairs

Mutation

Inherited alteration of genetic material
Chromosome aberrations
Mutation hot spots

Single Gene Mutation Types

Base pair substitution:
- Silent: Replaces base but no change in amino acid.
- Missense: Different amino acid produced.
- Nonsense: Codes for premature stop codon.
Frameshift mutation: Insertion or deletion of base pairs not in multiples of 3 (codons).
- Frameshift changes the reading frame.
- Inframe: Insertion/deletion in multiples of 3, no frameshift.

Mutagens

Agents that increase mutation frequency (teratogens).
Examples: Radiation, chemicals (nitrogen mustard, vinyl chloride, formaldehyde).
Affect the developing fetus after 2 weeks of implantation.

Genetic Terms

Locus: Gene's position on a chromosome.
Allele: Different form of a gene at a given locus.
Polymorphism: Locus with two or more alleles at appreciable frequency.
Heterozygous: Different alleles (Bb).
Homozygous: Identical alleles (bb).
Genotype: Gene composition at a specific locus.
Phenotype: Outward appearance.
Penetrance: Percentage of individuals with a genotype expressing the phenotype.
- Incomplete penetrance: Individuals with the gene but not expressing the disease.
Expressivity: Extent of phenotype variation with a particular genotype.
- Caused by modifier genes, environmental factors, different mutations.
Pedigrees: Family tree showing genetic disease tracking.
- Types of disorders:
  - Single gene
  - Chromosomal
  - Multifactorial

Autosomal Dominant Inheritance

Single gene defect
No generational skipping
Affected offspring can have a normal or heterozygous parent.
Allele can be disease-causing or normal.
Recurrence risk for offspring is 50%.

Autosomal Recessive Inheritance

Single gene defect
Both parents need to contribute the affected allele.
Skips generations.
Parents of affected children are typically heterozygous carriers.
Recurrence risk is 25%
Consanguinity (inbreeding) increases risk.

Sex-Linked Inheritance (X-linked)

Mostly affects males.
Examples: Duchenne muscular dystrophy.
Characteristics:
- More males than females affected.
- Fathers pass it to daughters but not sons.
- Can skip generations.
Most X-linked disorders are recessive.
Sons of female carriers have a 50% risk of being affected.

Chromosome Disorders

Autosomes (first 22 pairs), homologous.
Sex chromosomes.
Karyotype/karyogram: Chromosome picture.
Chromosome aberrations:
- Euploid: Multiple of normal chromosome number (diploid/haploid).
Polyploid: More than diploid number of chromosomes.
- Triploidy (3 copies, 69 chromosomes)
- Tetraploidy (4 copies, 92 chromosomes) – Not compatible with life.
Aneuploidy: Not a multiple of 23.
- Trisomy (3 copies)
- Monosomy (1 copy)
- Nondisjunction: Failure of homologous chromosome/sister chromatids to separate in meiosis/mitosis.
  - Usual cause of aneuploidy.
- Autosomal aneuploidy: Examples: Down syndrome (trisomy 21), Cri-du-chat syndrome, Fragile X syndrome
Partial trisomy: Only a portion of a chromosome is extra (ex. Down's Syndrome - trisomy 21)

Multifactorial Genetic Disorders

Polygenic traits: Variations caused by several loci.
Multifactorial traits: Genetic and environmental factors influencing the trait.
Threshold of liability: Certain level of risk factors needed for a disorder to occur.

Epigenetics

Biological mechanisms that turn genes on or off.
Mechanisms:
- DNA methylation
- Histone modification (acetylation/deacetylation)
Chromatin: DNA association with histones that affects gene expression.

RNA Based Mechanisms

Noncoding RNA (ncRNA) roles in RNA splicing, DNA replication, and RNA interaction.
MicroRNAs (miRNA): Modulate mRNA stability and translation.
- Oncomirs: miRNAs stimulating cancer.

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Description

This quiz covers the fundamental concepts of genetics, including embryonic stem cells, the structure of DNA, and various types of mutations. You'll explore somatic cells, gametes, and the impact of mutagens on genetic material. Test your knowledge on the mechanisms and implications of genetic mutations.