Lecture 2 - Genetics Flashcards
Gene:
a sequence of nucleotides that represents a functional unit of inheritance; a region of DNA that codes for a product, either RNA or protein.
Chromosome:
a highly ordered structure composed of DNA and proteins that carries the genetic information. In humans, there are 46 chromosomes ordered in pairs
Chromatid:
one half of a replicated chromosome that contains all of the genetic material equivalent to a chromosome. This is usually seen at metaphase.
Centromere:
the primary constriction of a chromosome; the point at which the chromatids are held together at metaphase. This region is comprised of repeat sequence DNA.
Karyogram:
an image of the chromosome constitution of an individual. Also, a figure showing the paired chromosomes from a cell arrayed in a standard sequence.
Autosome:
all chromosomes other than the X and Y chromosomes which are designated the sex chromosomes.
Homologous chromosomes or homologs
sister chromosomes, the members of a pair of chromosomes in which one is inherited from the mother and the other from the father.
Disomy:
the presence of 2 chromosomes.
Isodisomy:
2 chromosomes from the same source, i.e., duplication of 1 chromosome.
Heterodisomy:
2 different chromosomes
Locus:
position of a gene on chromosome
Allele:
an alternative form of a gene occupying the same locus. An allele may be the result of a mutation. There is a maximum of two alleles per diploid chromosome complement (one allele per chromosome), but multiple alleles may exist within a population.
Mutation:
a permanent heritable change in the sequence of genomic DNA. This may manifest at both the molecular and cytogenetic levels. Not all mutations are negative events. Many are benign (i.e., blue eye color) and some have positive effects (i.e., sickle cell trait in countries with significant risk of malaria).
Constitutional Mutation
a permanent heritable change in the sequence of genomic DNA. This may manifest at both the molecular and cytogenetic levels. Not all mutations are negative events. Many are benign (i.e., blue eye color) and some have positive effects (i.e., sickle cell trait in countries with significant risk of malaria).
Acquired mutation
may arise in a single somatic cell which then divides mitotically giving rise to a new clone of cells. The mutation will be limited to this clone and will not be transmitted to progeny of the individual. ie - cancer
Syndrome:
A disorder with a set of characteristics that occur together and are assumed to have a common basis. Not all characters occur in all affected individuals. There is a range of variability within a population.
Diploid:
the presence of two copies of each unique chromosome per cell. In humans, the chromosomes occur in pairs and the diploid (2N) number is 46.
Haploid:
one copy of each unique chromosome. In humans, the gametes are haploid (N = 23)
Recombination:
the generation of new allelic combinations on chromosomes, usually by crossing over
Mitosis
somatic cell division in which the DNA replicates and is even distributed to two equal daughter cells
Meiosis
cell division in the gonads that produces the gametes. A single DNA replication is followed by two cell divisions which reduces the total DNA content of a cell from 2N to N. Recombination occurs to increase genetic diversity in a population.
Cross-over
an exchange between homologous chromosomes resulting in a reassortment of the genes/alleles present on each chromosome
Nondisjunction
failure of chromosomes or chromatids to separate to opposite poles in cell division. Usually results in one too many or one too few chromosomes in a cell.
Biochemical genetics
subspecialty that deals with the diagnosis, treatment, and research of inborn errors of metabolism (mutations of biochemical pathways)
Examples of a simple biochemical pathway?
Describe PKU (phenylketonuria)…
Phenylalanine hydroxylase isn’t able to convert phenylalanine to tyrosine. Small amount of PHE converted to phenylpyruvic acid - can be detected in urine. Affects 1/10,000 births, autosomal recessive, treat by diet modification
Can lead to mental retardation
What are the other types of hyperphenylalaniemias?
Describe what occurs with the loss of function of tetrahydrobiopterin (BH4)…
BH4 is the cofactor that is in the signlaing pathway of phenylalanine hydroxylase. When knocked out, it causes the same clinical phenotype as PKU.
Cytogenetics
The study of the structure and function of the cell, especially the chromosomes
Describe the process of spermatogenesis
Oogenesis
Describe the timing of oogenesis
Oogenesis begins in the devloping fetues - by the 3rd month of gestation, primary oocytes are present. These cells reach prophase 1 by birth are remain so until ovulation. At ovulation, the oocyte completes meiosis 1, becoming a secondary oocyte. Meiosis will only be completed if fertilization occurs. Penetration of the sperm head stimulates the final division and release of second polar body.
Describe the main differences between spermatogenesis and oogenesis.
