front 1 Genetic variation | back 1 refers to differences between members of - allelic variation: due to differences in particular genes - chromosomes: vary in structure (chromosome segments can be deleted, duplicated, and/or rearranged) & number (# individual chromosomes may vary (3 not 2) or numbers of chromosome sets (4 sets not the usual 2) |
front 2 Cytogenetics | back 2 field of genetics that involves the microscopic examination of chromosomes |
front 3 Cytogeneticist | back 3 examines the chromosomal composition of a particular cell or organism - allows detection of individuals with abnormal chromosome number or structure - provides a way to distinguish b/w species (human vs fruit fly vs corn) |
front 4 Cytogeneticists use three main features to identify and classify chromosomes: | back 4 1. Location of centromere 2. Size 3. Banding patterns N: these features are all seen in a karyotype |
front 5 Karyotype | back 5 an individual's complete set of chromosomes N: seen by micrograph |
front 6 G banding | back 6 Chromosomes are exposed to the dye Giemsa - shows dark and light bands - 300 G bands seen in metaphase, 800 G bands in prometaphase |
front 7 The G banding pattern is useful because: | back 7 - distinguishes individual chromosomes from each other - detects changes in chromosome structure reveals evolutionary relationships among the chromosomes of closely related species |
front 8 Comparison of centromeric locations: metacentric, submetacentric, acrocentric, telocentric | back 8 See image |
front 9 2 Two primary ways chromosome structures can be altered | back 9 1. Total amount of genetic material in the chromosome can change - deletion (deficiency): loss of a chromosomal segment - duplication: repetition of a chromosomal segment compared to a normal chromosome 2. Total amount of genetic material remains the same but is rearranged - inversion: change in the direction of part of the genetic material along a single chromosome - translocation: a segment of one chromosome becomes attached to a different chromosome |
front 10 Simple translocation | back 10 A piece of a chromosome is attached to another chromosome |
front 11 Reciprocal translocations | back 11 Two different types of chromosomes exchange pieces, producing two abnormal chromosomes with translocations. Two non-homologous chromosomes exchange genetic
material Leads to a rearrangement of the genetic material, not a change in
the total amount Unlike reciprocal translocations, some translocations alter the
total amount of genetic material |
front 12 Terminal deletion | back 12 a deletion that occurs towards the end of a chromosome; during chromosomal deletion, the chromosome breaks in two pieces and the fragment w/o the centromere is lost |
front 13 Interstitial deletion | back 13 a deletion that occurs from the interior of a chromosome; chromosome breaks in two places, central fragment is lost, two outer pieces reattach |
front 14 Phenotypic consequences of deletion depends on | back 14 - size of deletion - chromosomal material deleted (are they vital) |
front 15 Cri-du-chat syndrome | back 15 detrimental condition caused by chromosomal deletion in the short arm of chromosome 5 |
front 16 Duplication | back 16 chromosomal duplication is usually caused by abnormal events during recombination - repetitive sequences (shown in red): can cause misalignment between homologous chromosomes - If a crossover occurs, nonallelic homologous recombination results |
front 17 Phenotypic consequences of duplications | back 17 - tend to be correlated to size (bigger piece, more likely to have effect) - end to have less harmful effects the deletions of comparable size |
front 18 Gene family | back 18 consists of two or more genes in a single species that are derived from the same ancestral gene. N: The majority of small chromosomal duplications have
no |
front 19 Paralogs | back 19 homologous genes within a single species N: Homolog is the umbrella term for a genes that share origin. Orthologs are two genes in two different species that share a common ancestor, while paralogs are two genes in the same genome that are a product of a gene duplication event of the original gene. |
front 20 Copy Number Variation (CNV) | back 20 segment of DNA that varies in copy number among members of the same species - may be missing a particular gene - may be a duplication |
front 21 Possible mechanisms of CNV (Copy Number Variation) | back 21 - nonallelic homologous recombination - proliferation of transposable elements (mobile DNA sequences capable of replicating themselves within genomes independently of the host cell DNA) - errors in DNA replication |
front 22 CNV associated w some human diseases | back 22 -Schizophrenia - Autism and some certain learning disabilities - Susceptibility to infectious diseases - Cancer |
front 23 Pericentric inversion | back 23 the inverted segment includes the centromere (with both arms involved) |
front 24 Paracentric inversion | back 24 the two breaks appear on the same side of the centromere (in the same arm). |
front 25 Break point effect: | back 25 An inversion break point occurs within a vital gene, thereby separating it into 2 nonfunctional parts |
front 26 Position effect: | back 26 A gene is repositioned in a way that alters its gene expression |
front 27 Inversion heterozygote | back 27 Individuals with one copy of a normal chromosome and one copy of an
inverted chromosome |
front 28 Inversion Heterozygotes: | back 28 During meiosis I, pairs of homologous sister chromatids synapse with
each other |
front 29 Robertsonian Translocation | back 29
Familial Down Syndrome is an example of
Robertsonian |
front 30 Euploidy | back 30 Variation in the number of complete sets of chromosome |
front 31 Aneuploidy | back 31 Variation in the number of particular chromosomes within a set - trisomic: organism has 3 copies of a chromosome instead of 2 - monosomic: 1 copy instead of 2 Commonly causes an abnormal phenotype Imbalance of gene products produce individuals that are less likely to survive than a euploid individual. Alterations in chromosome number occur frequently during gamete formation. The autosomal aneuploidies compatible with survival are trisomies 13, 18 and 21. Aneuploidies involving sex chromosomes generally have less severe effects than those of autosomes. |
front 32 Polyploid | back 32 Organisms w/ 3 or more sets of chromosomes |
front 33 Gene mutations | back 33 molecular changes in the DNA sequence of a gene - can involve a base substitution e.g. T -> G |
front 34 Transition | back 34 a change of a pyrimidine (C. T) to another pyrimidine or a purine (A, G) to another purine |
front 35 Transbersion | back 35 a change of a pyrimidine to a purine or vice versa |
front 36 Silent mutations | back 36 base substitutions that don't alter the amino acid sequence of the polypeptide |
front 37 Missense mutations | back 37 base substitutions in which an the amino acid change does occur |
front 38 Nonsense mutations | back 38 base substitutions that change a normal codon to a stop codon |
front 39 Frameshift mutations | back 39 involve the addition or deletion of a number of nucleotides that is not divisible by 3 shifts the reading frame so that translation of mRNA results in a completely different amino acid downstream of the mutation |
front 40 Endopolyploidy | back 40 Diploid animals that sometimes produce polyploid tissues |
front 41 Polytene Chromosomes | back 41 bundle of chromosomes that lie together in a parallel fashion - bundle is made from doublings of drosophila chromosome pairs wherein chromosomes undergo repeated rounds of replication w/o cellular division |
front 42 3 natural mechanisms that cause the | back 42 1. Meiotic nondisjunction |
front 43 Nondisjunction in meiosis I | back 43 failure of chromosomes to segregate properly during anaphase During fertilization, some gametes produce an individual that is trisomic
|
front 44 Nondisjunction in Meiosis II | back 44 If nondisjunction occurs in meiosis II, 50% Abnormal gametes |
front 45 Meiotic Nondisjunction | back 45 In rare cases, all the chromosomes can undergo nondisjunction and
migrate to one daughter cell |
front 46 Mitotic Abnormalities | back 46 Abnormalities in chromosome number often occur after fertilization. - if so, abnormality occurs during mitosis not meiosis 1. Mitotic nondisjunction: sister chromatids separate improperly (leads to trisomic and monosomic daughter cells) 2. Chromosome loss: one of sister chromatids do not migrate to a pole (leads to normal and monosomic cells) |
front 47 Mosaicism | back 47 genetic abnormalities that occur after fertilization - contains a subset of cells genetically different from the rest of the organism - size and location of the mosaic region depends on the timing and location of the original abnormality extreme case: abnormality takes place early embryonic development (precursor to be large segment of organism) |
front 48 Comparison of Autopolyploidy, Alloploidy, and Allopolyploidy | back 48 The number of chromosome sets in a given individual or species can
vary in three ways - species 1, species 2 -> alloploidy (allodipoid) - species 1, species 2 -> alloploidy (allotetraploid) |