Lec 54: Medical Genetics I: Introduction to Medical Genetics Flashcards
(31 cards)
Chromosomal disorders:
Chromosomal disorders: Due to gain or loss of segments or entire chromosomes
Single gene disorders:
Single gene disorders: Due to individual mutant genes
Multifactorial disorders:
Multifactorial disorders: Due to multiple genes, often acting in concert with environmental factors
Allele:
Allele: one of the different forms (variants) of a gene within a population
Homozygote:
Homozygote: An individual with two identical alleles
Heterozygote:
Heterozygote: An individual with two different alleles
Hemizygote:
Hemizygote: An individual with only one allele, chromosome or chromosome segment, instead of the usual two
Dominant trait (or allele):
Dominant trait (or allele): one that is expressed in the heterozygote
Recessive trait (or allele):
Recessive trait (or allele): one that is expressed only in homozygotes or hemizygotes
Genotype:
Genotype: genetic constitution; the genotypic ratio in the offspring is 1CC : 2Cc : 1cc.
Phenotype:
Phenotype: observable expression of genes; if c is recessive, the phenotypic ratio in the offspring is 3 normal : 1 affected.
Carrier:
Carrier: heterozygote for a mutant allele; generally used for a recessive disorder.
Explain Mendel’s insights into the nature of inheritance and how traits are transmitted from parent to offspring.
Each physical trait (such as plant height and flower color in peas) is controlled by a pair of hereditary determinants (genes). For each trait, an individual inherits one gene from the father and one from the mother. Law of segregation: Each gamete (oocyte or sperm) receives only one allele of a pair, and alleles segregate equally. That is, if an individual is heterozygous (Cc), half the gametes will receive the C allele, and half will receive the c allele.
How many stages of meiosis are there and generally happens?
Meiosis I: Chromosomes divide (diploid) Meisosi II: Chromatids divide (haploid)
Relate meiosis and Mendel’s laws of segregation and independent assortment of genes:
Accounts for Mendel’s laws of segregation and independent assortment of genes. During meiosis, the homologs segregate away from each other. Each gamete receives only one chromosome from each homologous pair and thus only one allele of each pair. This accounts for equal segregation of alleles, and allows one to predict the types and frequencies of offspring of a particular mating. The independent assortment of genes arises from the fact that each pair of chromosomes segregates independently from the others. If two genes controlling different traits are located on different chromosomes, all combinations of alleles are possible, depending on how the chromosomes line up on the equator at metaphase in meiosis I. Thus, an individual who is heterozygous for each of two gene pairs on different chromosomes (Aa Bb) would produce four kinds of gametes: AB, Ab, aB, and ab
Describe the basic organization of chromosomes and list the major components and their characteristics.
Basic organization: chromosome have a telomere with a short and long arm divide by a centromere. The structure and number of chromosomes (karyotype) is characteristic for each species. A standard description of a karyotype lists the total number of chromosomes, followed by the sex chromosome constitution and a description of any chromosomal abnormalities that may be present; 46,XY indicates a normal male karyotype.
Describe the normal human karyotype:
Normal karyotype: Male46, XY Female46, XX
Telomere:
Telomere: chromosome end Centromere: heterochromatin to which the spindle fibers attach during cell division Metacentric: having the centromere in the middle Submetacentric: having the centromere somewhat distant from the middle Acrocentric: having the centromere near the telomere
Centromere
Centromere: heterochromatin to which the spindle fibers attach during cell division
Metacentric
Metacentric: having the centromere in the middle
Submetacentric
Submetacentric: having the centromere somewhat distant from the middle
Acrocentric
Acrocentric: having the centromere near the telomere
Describe chromosomal numerical abnormalities:
Numerical abnormalities: The terms euploid and aneuploid are frequently used to refer to numerical abnormalities.
- Euploid: describes an exact multiple of the number of chromosomes in a normal gamete
- Aneuploidy usually refers to the gain or loss of a single chromosome. Aneuploidy arises during mitosis or meiosis by a failure of chromosomes to separate normally (nondisjunction). If one set of chromatids fails to separate, one of the daughter cells will be trisomic and the other will be monosomic for that particular chromosome.
- If nondisjunction occurs during embryonic development, the individual will be a mosaic of normal and abnormal cells, unless the nondisjunction occurs at the first mitotic division in which case all cells will be aneuploid.
- Aneuploidy for one or more chromosomes is also a common feature of human cancers.
- Cancer cells can be also polyploid, i.e., have more than two complete sets of chromosomes.
- Aneuploidy for one or more chromosomes is also a common feature of human cancers.
- If nondisjunction occurs during embryonic development, the individual will be a mosaic of normal and abnormal cells, unless the nondisjunction occurs at the first mitotic division in which case all cells will be aneuploid.
What is a chromosomal structural abnormalities?
Structural abnormalities: Chromosome structural abnormalities can result in the gain or loss of portions of chromosomes, chromosome fusions, inversions of portions of chromosomes or exchange of material between chromosomes.
