Basic genetics and molecular biology

Question 1

What are a gene?

Answer 1

Genes are the unit of inheritance: Genes are pieces of DNA that contain information for the formation on proteins, RNA, and non-coding RNAs

Question 2

What is a phenotype?

Answer 2

The observable traits of the organism are called its phenotype.

Genotype is one of three factors that determine phenotype, the other two being inherited epigenetic factors, and non-inherited environmental factors.

Question 3

What is a genotype?

Answer 3

The genetic background or an organism - the set of alleles for a given organism is called its genotype

Question 4

What are a locus (loci) and alleles?

Answer 4

The position of a gene on a chromosome. A variant of the similar DNA sequence located at a given locus is called an allele.

Question 5

What does homozygous and heterozygous mean (in genetics)?

Answer 5

Homozygous: Same allele at a given locus
Heterozygous: Different allele at a given locus

Question 6

Wild type mean?

Answer 6

The most frequent allele of a gene in a given population

Think: “What is in the wild (typical)?” -> The most frequent one stupid!

Question 7

Law of Segregation

Answer 7

The “First Law” states that the two alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes.

Allele pairs separate randomly in, or segregate, from each other during the production of gametes: egg and sperm. Because allele pairs separate during gamete production, a sperm or egg carries only one allele for each inherited trait. When sperm and egg unite at fertilization, each contributes its allele, restoring the paired condition in the offspring

Question 8

Law of Independent Assortment

Answer 8

The “Second Law”, also known as “Inheritance Law”, states that separate genes for separate traits are passed independently of one another from parents to offspring.

Question 9

Law of Dominance

Answer 9

The “Third Law” states that recessive alleles will always be masked by dominant alleles. Therefore, a cross between a homozygous dominant and a homozygous recessive will always express the dominant phenotype, while still having a heterozygous genotype.

Question 10

Mendelian trait. If a mutation cause a disease in one of these traits we call it?

Answer 10

A Mendelian trait is one that is controlled by a single locus in an inheritance pattern.

In such cases, a mutation in a single gene can cause a disease that is inherited according to Mendel’s laws. These diseases are called monogenic diseases.

Question 11

Dominantly inherited diseases

Answer 11

Only one faulty gene is enough to cause a disase

E.g. Huntington`s disease and familiar hypercholesterolemia

Question 12

Recessive diseases

Answer 12

Both genes have to be mutated to cause a disease. If only one is mutated, the normal variant can compensate.

E.g. cystic fibrosis and albinism

Question 13

Codominant inheritance

Answer 13

A variation of the dominant-recessive inheritance. In case of codominant inheritance two different alleles of a gene can be expressed, and each version makes a slightly different protein. Both alleles influence the genetic trait or determine the characteristics of the genetic condition.

E.g. blood type AB is inherited in a codominant pattern. Here the A and B blood group is dominant over 0 blood group and show codominant inheritance to each other. It means that if a person has one gene for A blood group, one for 0 blood group then his/her blood group will be A, in the case of one A and one B, the blood group will be AB.

Question 14

Genetic pleiotropy

Answer 14

The gene participates in several metabolic pathways, which have effects on different organs or tissues. In this case mutations in this gene can have different consequences. It is called genetic pleiotropy. A classic example of pleiotropy is the human disease phenylketonuria (PKU).

Question 15

What is a Barr body?

Answer 15

The inactive X chromosome in a female somatic cell

Question 16

Linked inheritance

Answer 16

If two genes are close to each other on a chromosome, then the associated traits inherited together. In this case the Mendel’s first and second laws are not valid and this phenomenon is called linked inheritance and the two genes are in linkage.

Question 17

When does crossing over (or homolongous recombination) occur?

Answer 17

In meiosis 1: during this phase the alleles of the two chromosomes exchange with each oter

Question 18

What does chiasma mean in genetics?

Answer 18

Chiasma = crossing over

In genetics, a chiasma is the point where two homologous non-sister chromatids exchange genetic material during chromosomal crossover in meiosis (sister chromatids also form chiasmata between each other (also known as a chi structure), but because their genetic material is identical, it does not cause any noticeable change in the resulting daughter cells). The chiasmata become visible during the diplotene stage of prophase I of meiosis 1, but the actual “crossing-over” of genetic material is thought to occur during the previous pachytene stage. When each tetrad, which is composed of two pairs of sister chromatids, begins to split, the only points of contact are at the chiasmata.

Question 19

Name 5 chromosome mutations

Answer 19

Duplication
Deletion
Translocation
Inversion
Insertion

Question 20

What are the “central dogma” in molecular biology?

Answer 20

DNA makes RNA, RNA makes protein.

Question 21

Backbone of DNA

Answer 21

phosphate + sugar residue (2-deoxyribose - a pentose)

Linked between the 3rd and 5th carbon. Phosphodiester bond

Question 22

What are the 4 bases used in DNA? Which bond to what?

Answer 22

Adenine, thymine, cytosine and guanine

Purine bonds to pyrimidines with complementary base pairing:
A-T (2 H-bonds)
C-G (3 H-bonds)

Uracil are used in RNA. Its a thymine without a methyl group. Uracil can also be promed in the breakdown of cytosine.

Question 23

The term polymorphism should only be used for in the context of a …?

Answer 23

population

Question 24

What are the two most common spontaneous DNA mutations?

Answer 24

1: deaminations, and 2: depurinations
1: during deamination cytosine is converted to uracil, and adenine to hypoxanthine
2: during depurination the sugar-phosphate backbone of DNA remains intact, but the purine base are lost