INHERITANCE AT THE MOLECULAR LEVEL Flashcards
Describe autosomal recessive trait or disorder.
Both alleles must code for the trait or disease in order for the person to express the trait (or disease). Affects both genders equally, and has horizontal distribution (may not be present in every generation)
Describe the occurrence of sex-linked disorders.
virtually all sex-linked disorders involve the X chromosome, and most are recessive. They can occur in women, but are more common in men as they have 1 X chromosome.
Describe the mitochondrial genome.
Circulare piece of DNA with about 60 genes. Inherited maternally. Usually women pass their mitochondrial DNA on to their children whereas men do not.
Describe the packaging of nuclear DNA.
Human genome contains about 30k genes. Each linear strand of DNA (chromosome) is usually tightly coiled and supercoiled, allowing the large volume of genetic material to be packaged into very small volumes.
Histone proteins help to stabiliste the tightly coiled DNA structure.
Describe how chromosomes are studied.
- live cells are collected (blood or foetal cells) and cultured for 48-72 hours.
- cell division is arrested in metaphase, which is when chromosomes are visible.
- The cell nucleus is then ruptures, and chromosomes are stained (either histochemically, radio labelled or fluorescently labelled).
- Chromosomes are displayed via karyotyping.
What is a karyotype?
The full complement of chromosomes is called the karyotype. It refers to both the number of chromosomes and their structural features, such as shape, size and composition.
Describe the visible features in a karyotype/
Heterochromatin: comprised mainly of repetitive non-coding DNA, appears as darkly stained condensed chromosomal regions.
Euchromatin: thought to contain the functional genes, appears as weakly stained and less condensed chromosomal regions.
Describe the structure of chromosomes.
short arm (p) and long arm (q). Centromere attaches to the spindle during cell division. Telomeres are present at the terminus of the chromosome.
Describe the human karyotype.
23 pairs of chromosomes.
22 pairs of autosomes and 1 pair of sex chromosomes. the Y chromosome is much smaller than the X chromosome.
What is Mendel’s first law (principle of segregation)?
The two members of a gene pair segregate equally into the gametes.
Briefly describe how segregation in meiosis leads to 4 gametes.
Diploid cell (containing pair of sex chromosomes, undergoes meiosis 1, in which the cell divides to produce 2 haploid daughter cells (each have one of the sex chromosomes). These cells then undergo meiosis 2, in which the sister chromatids separate to form 2 gametes each --> 4 gametes. The chromosomes are segregated equally and randomly into the gametes.
What is Mendel’s second law (principle of independent assortment)?
Different gene pairs assort independently in gamete formation. (does not generally occur for genes on the same chromosome).
Describe diploid cells.
Have 2 copies of each chromosome per cell, therefore 2 copies of each gene per cell. The matched genes occur at the same locus on each of the 2 chromosomes.
