Medical genetics Wk 1

Question 1

what is genetics

Answer 1

the study of hereditary

Question 2

what is hereditary

Answer 2

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

Question 3

what were Mendel’s three postulates or principles of inheritances

Answer 3

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.

Question 4

Modern genetic terminology
what is a chromosome

Answer 4

Structural unit of genetic material

Question 5

what is a gene

Answer 5

A sequence of nucleotides that encodes the production of polypeptides

Question 6

what is genetic code

Answer 6

The deoxynucleotide triplets that encode the 20 amino acids or specify
initiation or termination of translation.

Question 7

what is an allele

Answer 7

One of the possible alternative forms of a gene, often distinguished from other alleles by phenotypic effects.

Question 8

what is an autosome

Answer 8

A non-sex chromosome.

Question 9

what is a gamete

Answer 9

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.

Question 10

what is chromatin

Answer 10

The complex of DNA, RNA, histones, and nonhistone proteins that make up uncoiled chromosomes, characteristic of the eukaryotic interphase nucleus.

Question 11

what two factors do pedigree single gene disorders depend on

Answer 11

1. whether the phenotype is dominant or recessive
2. the chromosomal location of the gene locu which may be an autosome (1 to 22) or on a sex chromosome (x and Y

Question 12

explain the chromosome theory of inheritance

Answer 12

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.

Question 13

what happens in mitosis

Answer 13

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.

Question 14

what happens in meiosis

Answer 14

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)

Question 15

what is a mutation

Answer 15

Mutations are defined as any heritable change in the DNA sequence and are the source of all genetic variation.

Question 16

what is a karyotype

Answer 16

an individual’s collection of chromosomes

Question 17

what happens to telomeres

Answer 17

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

Question 18

what is the difference between an autosome and a sex chromosome

Answer 18

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

Question 19

How we determine chromosomal location of a gene

Answer 19

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.

Question 20

the human genome

Answer 20

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.

Question 21

the organisation of the human genome

Answer 21

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”).

Question 22

Incomplete, or Partial, dominance

Answer 22

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.

Question 23

Tay Sachs Disease - incomplete dominance

Answer 23

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

Question 24

physical effects of tay sachs diease

Answer 24

nerve cells destroyed in brain and spinal cord

symptoms appear 3-6 months after birth

loss of motor control, atrophy of muscles, seizures

death

Question 25

what is Tay-Sachs disease

Answer 25

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.

Question 26

What is a chromosome

Answer 26

Threadlike structures made of DNA molecules that contain the genes

Question 27

What is the genotype

Answer 27

The genetic makeup of the organism - so therefore the organism’s complete set of genes

Question 28

What is a phenotype

Answer 28

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

Question 29

What is incomplete dominance

Answer 29

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

Question 30

A characteristic that an organism can pass on to its offspring through its genes

Answer 30

Trait

Question 31

Homozygous

Answer 31

Having two identical alleles for a trait

Question 32

What is DNA

Answer 32

the genetic material that keeps information
about an organism and is passed from parent to offspring

Question 33

What are sister chromatids

Answer 33

• two identical chromosomes that split and
contain the same genetic material

Question 34

What is a centromere

Answer 34

a specialized condensed region of each
chromosome that appears during mitosis
where the chromatids are held together to
form an X shape

Question 35

What is the karyotype

Answer 35

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)

Question 36

What are sex chromosomes

Answer 36

one of the 23 pairs of chromosomes in the
human, contains genes that will determine the
sex of the individual

Question 37

What is a metacentric chromosome

Answer 37

• Has centromere in middle of the chromosome
- equal arms

Question 38

What is a submetacentric chromosome

Answer 38

Having one arm longer than the other

Question 39

• When preparing to divide, where are sister
chromatids connected?

Answer 39

Centromere

Question 40

What is codominance

Answer 40

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

Question 41

What are the two parts of gene

Answer 41

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