Medical genetics Wk 1 Flashcards
what is genetics
the study of hereditary
what is hereditary
a biological process where a parent passes certain genes to their offspring. the genetic information lies within the cell nucleus of each living cell in the body
what were Mendel’s three postulates or principles of inheritances
UNIT FACTORS IN PAIRS
genetic characteristics are controlled by a specific unit factor that exists for each trait. each diploid individual receives one factor from each parent
DOMINANCE/RECESSIVNESS
When two unlike unit factors responsible for a single character are
present in a single individual, one unit factor is dominant to the
other, which is said to be recessive.
SEGREGATION
during the formation of gametes, the paired unit factors separate randomly so that each gmaete receives one or the other with equal likelihood
These provide a suitable explanation for the results of monohybrid crosses
INDEPENDENT ASSORTMENT
During gamete formation, segregating pairs of unit factors assort independently of each other.
Modern genetic terminology
what is a chromosome
Structural unit of genetic material
what is a gene
A sequence of nucleotides that encodes the production of polypeptides
what is genetic code
The deoxynucleotide triplets that encode the 20 amino acids or specify
initiation or termination of translation.
what is an allele
One of the possible alternative forms of a gene, often distinguished from other alleles by phenotypic effects.
what is an autosome
A non-sex chromosome.
what is a gamete
A specialized reproductive cell with a haploid number of chromosomes.
An individual’s genotype is the totality of that individual’s hereditary material, whereas an
individual’s phenotype is the individual’s appearance.
what is chromatin
The complex of DNA, RNA, histones, and nonhistone proteins that make up uncoiled chromosomes, characteristic of the eukaryotic interphase nucleus.
what two factors do pedigree single gene disorders depend on
- whether the phenotype is dominant or recessive
- the chromosomal location of the gene locu which may be an autosome (1 to 22) or on a sex chromosome (x and Y
explain the chromosome theory of inheritance
in most eukaryotes, members of each species have a characteristic number of chromosomes called the diploid number (2n)
Chromosomes in diploid cells exist in pairs, called homologous chromosomes.
what happens in mitosis
In mitosis chromosomes are copied and distributed so that each daughter cell receives a diploid set of chromosomes identical to those in the parental cell.
what happens in meiosis
Meiosis is associated with gamete formation. Cells produced by meiosis receive only one set of chromosome sfrom each chromosome pair, and the resulting number of chromosomes is called the haploid number (n)
what is a mutation
Mutations are defined as any heritable change in the DNA sequence and are the source of all genetic variation.
what is a karyotype
an individual’s collection of chromosomes
what happens to telomeres
telomeres get shorter each time a cell copies itself, but the important DNA stays intact
eventually they get too short causing the cells to age and they stop functioning properly
what is the difference between an autosome and a sex chromosome
autosome- are the first 22 homologous pairs of human chromosomes that do not influence the sex of the individual
sex chromosomes- are the 23rd pair of chromosomes that determine the sex of an individual
How we determine chromosomal location of a gene
each human chromosome has a short arm (“p” for
“petit”) and long arm (“q” for “queue”), separated by a centromere. The ends of the chromosome are called telomeres
A gene locus (locus means place) is the location of a gene in a chromosome; or rather, the position of the gene in a DNA molecule.
Each chromosome arm is divided into regions, or cytogenetic bands, that can be seen using a microscope and special stains.
the human genome
A genome is an organism’s complete set of genetic instructions.
* The genome contained in the nucleus of human somatic cells consists of 46 chromosomes, arranged in 23 pairs. Of those 23 pairs, 22 are alike in males and females and are called autosomes, numbered from the largest to the smallest. The remaining pair comprises the sex chromosomes: two X chromosomes in females and an X and a Y chromosome in males.
* In addition to the nuclear genome, a small but important part of the human genome resides in mitochondria in the cytoplasm. The mitochondrial chromosome has a number of unusual features that distinguish it from the rest of the human genome.
the organisation of the human genome
Regions of the genome with similar characteristics or organization, replication, and expression are not arranged randomly but rather tend to be clustered together. Some chromosome regions, or even whole chromosomes, are high in gene content (“gene rich”), whereas others are low (“gene poor”).
Incomplete, or Partial, dominance
While alleles are transmitted from parent to offspring according to Mendelian principles, they often do not display the clear-cut dominant /recessive relationship observed by Mendel.
For example, if a snapdragon plant with red flowers is crossed with a white-flowered plant, the offspring have pink flowers. Because some red pigment is produced in the F1 intermediate- colored plant, neither the red nor white flower color is dominant.
Tay Sachs Disease - incomplete dominance
Tay–Sachs disease, in which homozygous recessive individuals are severely affected with a fatal lipid-storage disorder.
It affects the HexA gene that encodes the production of beta hexose aminidase A which is responsible in lipid metabolism breaks down a fatty acid called GM2 ganglioside
Located on chromosome 15
The organelle affected is the lysosome
Mutations of the HexA gene cause this disease
physical effects of tay sachs diease
nerve cells destroyed in brain and spinal cord
symptoms appear 3-6 months after birth
loss of motor control, atrophy of muscles, seizures
death
what is Tay-Sachs disease
Tay-Sachs disease is a rare inherited disorder that progressively destroys nerve cells (neurons) in the brain and spinal cord.
Afflicted infants eventually become blind, deaf, mentally retarded, and paralyzed,
Mutations in the HEXA gene cause Tay-Sachs disease. The HEXA gene provides instructions for making part of an enzyme called β-hexosaminidase A, which plays a critical role in the brain and spinal cord.
What is a chromosome
Threadlike structures made of DNA molecules that contain the genes
What is the genotype
The genetic makeup of the organism - so therefore the organism’s complete set of genes
What is a phenotype
The observable characteristics in an individual resulting from the expression of genes - process in which information from a gene is used in the synthesis of a functional gene product
What is incomplete dominance
When a dominant allele or form of a gene, does not completely mask the effects of a recessive allele and the organism’s resulting physical appearance shows blending of both alleles
A characteristic that an organism can pass on to its offspring through its genes
Trait
Homozygous
Having two identical alleles for a trait
What is DNA
the genetic material that keeps information
about an organism and is passed from parent to offspring
What are sister chromatids
• two identical chromosomes that split and
contain the same genetic material
What is a centromere
a specialized condensed region of each
chromosome that appears during mitosis
where the chromatids are held together to
form an X shape
What is the karyotype
the appearance of the chromosomal makeup
of a somatic cell in an individual or species
(including the number and arrangement and
size and structure of the chromosomes)
What are sex chromosomes
one of the 23 pairs of chromosomes in the
human, contains genes that will determine the
sex of the individual
What is a metacentric chromosome
• Has centromere in middle of the chromosome
- equal arms
What is a submetacentric chromosome
Having one arm longer than the other
• When preparing to divide, where are sister
chromatids connected?
Centromere
What is codominance
Joint expression of both alleles in a heterozygote is called codominance
For codominance to be studied, both products must be phenotypically detectable. Example of codominance is the ABO blood-type system. The ABO system is characterized by the presence of antigens on the surface of red blood cells. The A and B antigens are under the control of gene, located on chromosome 9.
Combination of alleles in the ABO system exhibits a codominant mode of inheritance
What are the two parts of gene
Regulatory region - promoter region involved in the regulation of the expression of a gene
and the
coding region- coding of exons will be translated into proteins
