Genetics First Half Exam

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Histones

Back 1

Histones are the chief protein components of chromatin.

They act as spools around which DNA winds, and they play a role in gene regulation.

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Karyotype

Back 2

A karyotype is the characteristic chromosome complement of a eukaryote species.

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Sister Chromatids

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Sister chromatids are identical copies of a chromosome connected by a centromere.

Compare sister chromatids to homologous chromosomes, which are the two different copies of the same chromosome that diploid organisms (like humans) inherit, one from each parent.

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Metacentric

Back 4

A chromosome is metacentric if its two arms are roughly equal in length.

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Submetacentric

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If arms' lengths are unequal, the chromosome is said to be submetacentric.

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Acrocentric

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If the p (short) arm is so short that is hard to observe, but still present, then the chromosome is acrocentric.

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Size Vs. Content

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Larger chromosomes don't necessarily have more genes on them than smaller chromosomes.

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Mitosis

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Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two daughter nuclei.

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Interphase

Back 9

Chromosomes are invisible.

G1, S, G2 phases

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Prophase

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Chromosomes are just becoming visible.

Bipolar spindles are forming.

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Prometaphase

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Nuclear Envelope Breakdown.

Chromosomes continue to condense.

Spindles seperate.

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Metaphase

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Chromosomes condensed.

Chromosomes at metaphase plate.

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Anaphase

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Centromeric kinetochores split.

Chromosomes separate to opposite sides.

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Telophase

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Chromosomes decondensing.

Nuclear Envelope Re-forming.

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Cytokinesis

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Cytoplasmic division.

Actually happens at the same time as telophase.

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Meiosis

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process of reductional division in which the number of chromosomes per cell is halved.

Generates genetically distinct individuals in populations.

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Prophase I

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This is the most important phase in meiosis.

Crossing Over Happens Here.

Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis

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Crossing Over

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The exchange of genetic material between homologous chromosomes during prophase 1 of meiosis.

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Pseudoautosomal Regions

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The pseudoautosomal regions get their name because any genes located within them are inherited just like any autosomal genes.

Crossing over between the X and Y chromosomes is normally restricted to the pseudoautosomal regions.

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X-Inactivation

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X-inactivation (also called lyonization) is a process by which one of the two copies of the X chromosome present in female mammals is inactivated.

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Mosaicism

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Mosaicism denotes the presence of two populations of cells with different genotypes in one individual, who has developed from a single fertilized egg.

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Epigenetics

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Epigenetics refers to changes in phenotype (appearance) or gene expression caused by mechanisms other than changes in the underlying DNA sequence.

The best example of epigenetic changes in eukaryotic biology is the process of cellular differentiation.

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Non-disjunction

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Nondisjunction is the failure of chromosome pairs to separate properly during cell division.

This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis.

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Translocation

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Chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes

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Robertsonian Translocation

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This type of rearrangement involves two acrocentric chromosomes that fuse near the centromere region with loss of the short arms.

The resulting karyotype in humans leaves only 45 chromosomes since two chromosomes have fused together.

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Reciprocal Translocation

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Reciprocal translocations are usually an exchange of material between nonhomologous chromosomes.

Carriers of balanced reciprocal translocations have increased risks of creating gametes with unbalanced chromosome translocations

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Inversion

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An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end.

An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself.

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Gene Duplication

Back 28

Duplication of a region of DNA that contains a gene.

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Gene Deletion

Back 29

A mutation in which a part of a chromosome or a sequence of DNA is missing.

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Turner Syndrome

Back 30

Encompasses several conditions, of which monosomy X (deletion of an entire X chromosome) is most common.

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Klinefelter's Syndrome

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XXY

The principal effects are development of small testicles and reduced fertility.

The extra X chromosome is retained because of a nondisjunction event during meiosis (sex cell division).

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22q11 Deletion

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Velocardiofacial Syndrome, DiGeorge Syndrome

The deletion occurs near the middle of the chromosome at a location designated q11.2

Cleft Palate, Hypernasal Speech, Long Broad Nose

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22q11 Inverted Duplication

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Cat Eye Syndrome

The short arm (p) and a small section of the long arm (q) are present three (trisomic) or four times (tetrasomic) instead of the usual two times. The additional chromosome 22 usually arises spontaneously (de novo).

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Tay-Sachs Disease

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Inherited in an autosomal recessive pattern.

Ashkenazi Jews

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Huntington's Disease

Back 35

Autosomal Dominant Inheritance pattern.

Causes chorea later in life.

Can be screened for.

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Locus

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Locus (plural loci) is a fixed position on a chromosome such as the position of a biomarker that may be occupied by one or more genes.

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Allele

Back 37

One member of a pair or series of different forms of a gene. Usually alleles are coding sequences, but sometimes the term is used to refer to a non-coding sequence.

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Genotype

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The genotype is the genetic constitution of a cell, an organism, or an individual (i.e. the specific allele makeup of the individual) usually with reference to a specific character under consideration.

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Phenotype

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A phenotype is any observable characteristic or trait of an organism.

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Segregation

Back 40

When any individual produces gametes, the copies of a gene separate, so that each gamete receives only one copy.

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Independent Assortment

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Alleles of different genes assort independently of one another during gamete formation.

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Autosomal Dominance

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An autosomal dominant gene is one that occurs on an autosomal (non-sex determining) chromosome. As it is dominant, the phenotype it gives will be expressed even if the gene is heterozygous.

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Penetrance

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The proportion of individuals carrying a particular variation of a gene (an allele or genotype) that also express an associated trait.

For example, if a mutation in the gene responsible for a particular autosomal dominant disorder has 95% penetrance, then 95% of those with the mutation develop the disease, while 5% do not.

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Hereditary Hemorrhagic Telangiectasia

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Autosomal Dominant Inheritance

HHT is characterised by telangiectasia (small vascular malformations) on the skin and mucosal linings, epistaxis (nosebleeds), and arteriovenous malformations (AVMs) in various internal organs.

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van der Woude Sydrome

Back 45

consists of the following characteristics: cleft lip with or without cleft palate, isolated cleft palate, pits or mucous cysts on the lower lip, and hypodontia.

Autosomal dominant or sporadic inheritance

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Stickler Syndrome

Back 46

A group of genetic disorders affecting connective tissue, specifically collagen.

Autosomal dominant trait

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Autosomal Recessive Inheritance

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In contrast to an autosomal dominant trait, a recessive trait only becomes phenotypically apparent when two recessive alleles of a gene are present. In other words, the subject is homozygous for the trait.

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Dominant Negative

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"dominant negative" or antimorphic mutations occur when the gene product adversely affects the normal, wild-type gene product within the same cell.

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Gain-of-Function

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Change the gene product such that it gains a new and abnormal function. These mutations usually have dominant phenotypes. Often called a neomorphic mutation.

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Loss-of-Function

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The result of gene product having less or no function. When the allele has a complete loss of function (null allele) it is often called an amorphic mutation.

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Haploinsufficiency

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Haploinsufficiency occurs when a diploid organism only has a single functional copy of a gene (with the other copy inactivated by mutation) and the single functional copy of the gene does not produce enough of a gene product (typically a protein) to bring about a wild-type condition, leading to an abnormal or diseased state.

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Consanguinity

Back 52

> one ancestor in common
(up to great-grandparent).

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Inbred

Back 53

Offspring of marriage between
consanguinous individuals.

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Incest

Back 54

Consanguinous marriage
forbidden by law.

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Inbreeding increases

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Homozygosity (exposes recessive mutations)

Rates of Birth Defects

Mortality Rates

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Hemizygous

Back 56

A diploid organism is hemizygous for a particular gene when only one allele for the gene is present.

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X-Linked Recessive

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X-linked recessive is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be expressed (1) in males and (2) in females who are homozygous for the gene mutation

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Amelogenesis Imperfecta

Back 58

Most cases are caused by mutations in the ENAM gene and are inherited in an autosomal dominant pattern.

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Frameshift Mutation

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Due to the triplet nature of gene expression by codons, the insertion or deletion can disrupt the reading frame, or the grouping of the codons, resulting in a completely different translation from the original.

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Imprinting

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Genomic imprinting is a genetic phenomenon by which certain genes are expressed in a parent-of-origin-specific manner.

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Uniparental Disomy

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Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or part of a chromosome, from one parent and no copies from the other parent.

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Mitochondrial Inheritance

Back 62

In sexually reproducing organisms, mitochondria are normally inherited exclusively from the mother.

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Downs Syndrome

Back 63

Trisomy 21.

Results from non-disjunction (usually in the mother, but occasionally the father)

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Prader-Willi Syndrome

Back 64

Prader-Willi syndrome (abbreviated PWS) is a very rare genetic disorder, in which seven genes (or some subset thereof) on chromosome 15 are missing or unexpressed (chromosome 15q partial deletion) on the paternal chromosome.

Also an example of imprinting!

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Angelman Syndrome

Back 65

A classic example of genetic imprinting in that it is usually caused by deletion or inactivation of genes on the MATERNALLY inherited chromosome 15

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Trisomic Rescue

Back 66

A genetic phenomenon in which a fertilized ovum containing three copies of a chromosome loses one of these chromosomes to form a normal, diploid chromosome complement.

If both of the retained chromosomes came from the same parent, then uniparental disomy results.

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Monosomic Rescue

Back 67

The duplication of a chromosome from a monosomic zygote.

This would also lead to uniparental disomy.

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Gamete Complementation

Back 68

The fertilization of a gamete with two copies of a chromosome by a gamete with no copies of the same chromosome.

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Promoter

Back 69

Specifies where transcription begins.

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Coding Sequence

Back 70

Includes coding information for the polypeptide chain specified by the gene.

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Terminator

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Specifies the end of the mRNA transcript.

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Post-transcriptional Modification

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(1) removal of nucleotides from primary RNA transcripts (Splicing out introns)

(2) addition of nucleotides with sequences not encoded by the corresponding genes (Capping and Poly-A tails)

(3) covalent modification of certain bases. (Methylation of bases?)

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Introns

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Garbage areas of nucleic acids that split up the coding regions.

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Exons

Back 74

The coding regions in mRNA.

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Anti-codon

Back 75

Binds to a complementary triplet on the mRNA.

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Peptidyl Transferase

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Forms peptide links between adjacent amino acids using tRNAs during the translation process of protein biosynthesis.

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Signaling Sequences

Back 77

A short amino acid sequence at one end that functions like a postal code for the target organelle.

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Splice Site Mutation

Back 78

Is a genetic mutation that inserts or deletes a number of nucleotides in the specific site at which splicing of an intron takes place during the processing of precursor messenger RNA into mature messenger RNA.