Genetics

Genetics

What is Genetics?

Genetics = science of heredity. Concerns the structure and function of the genome. Occurrence of genetic changes and

Discovery of the DNA-molecule

• In 1953 James

Watson and Francis Crick discovered the structure of the

DNA- molecule.

DNA

• Deoxyribonucleic acid

• The genetic information is in the DNA-molecule.

• The “DNA-alphabet” consists of only 4 letters: A, T, G, C.

• Every word in DNA-

language consists of 3 letters.

Genes

• One gene is a certain segment of the DNA-molecule.

• A gene contains the plan for a certain protein.

• This protein (gene product) gives the organism a certain trait.

• All the genes of the

The structure of the DNA-molecule

• Double helix

• Shaped like spiral stairs/twisted rope ladder

• ”The ropes” consist of the sugar deoxyribose and phosphate.

• One “step” consist of

Nitrogen bases

• It is the sequence of the four nitrogen bases (A,T,C,G) that is the “language” of DNA.

• A = Adenine

• T = Thymine

• G = Guanine

Base paring

• Every ”step” in DNA consists of 2 nitrogen bases

• Adenin only pairs with Thymine (A-T) (T-A)

Nucleotide

One nucleotide consists of: • One phosphate

group

• One sugar

(deoxyribose)

Folding of the DNA-molecule

• The DNA-molecule is

packed at severeal levels.

• The chromosome consists of one long very tightly

packed DNA-molecule.

The two main tasks of DNA

• Copy itself = REPLICATION: Only happens

before cell division. When one cell becomes two the genetic material also needs to double itself.

Replication

• Before cell division all DNA in the cell must be copied (replicated)

• Each chromosome in the cell contains one long

single DNA-molecule.

Replication

DNA can copy itself:

• The double helix splits down the middle.

• The complementary bases are added to the two halfs of the split molecule.

Replication fork

• Topoisomerase unwinds DNA.

• Helicase separates the double strand.

The cell cycle

(Reparation and control)

Mitosis

• Interphase: DNA loosely packed in the nucleus, replication of DNA takes place.

• Prophase: Chromosomes tightly packed and visible in microscope. Nuclear membrane decomposes.

• Metaphase: Chromosomes line up in the middle of the cell.

• The sister chromatids are pulled to each side of the cell.

Interphase

Prophase

Metaphase

Mitosis

• Telophase: The remaining components of the cell are evenly allocated to the two daughter cells. New nuclear

membranes are formed.

• Cytokinesis: The cell is divided into two cells.

Telophase and cytokinesis

Meiosis (I)

• Meiosis only takes place in the sex-cells.

• Metaphase I: The chromosomes pair up in the middle of the cell.

• Anaphase I: The two chromosomes in the pair are pulled apart to opposite sides of the cell.

Interphase

Prophase I

Metaphase I

Anaphase I

Meiosis (II)

• Metaphase II: Chromosomes line up in the middle of the cell.

• Anaphase II: The sister chromatids are pulled

appart to opposide sides of the cell.

• Sex cells only contain one chromosome of each type. Interphase and

meisosis II

Metaphase II

Anaphase II

Telophase and cytokinesis

RNA

• RNA translates the code in DNA into proteins.

• RNA = ribonucleic acid

• RNA is singelstranded.

• Has the nitrogen base U (uracile) instead of T

• mRNA = messenger RNA

From DNA to proteins

• The information in

DNA is transcribed to mRNA.

• mRNA moves out of the nucleus.

• tRNA translates mRNA to amino acids in the ribosome.

Transcription

• In the nucleus: RNA-

nucleotides build mRNA with the open

DNA-molecule as a template.

• Only the sequenses

Splicing= introns are cut off

• In the genes there are both exons (coding DNA) and

introns (non-coding DNA).

The ribosome = the protein factory

• mRNA is transported from the nucleus to the ribosomes outside the nucleus.

codon – anti codon

• For each codon in mRNA (3

nitrogen bases) the tRNA-molecule with the correct 3 complementary nitrogen base (anti codon)

The genetic code

• Each codon correspond to a certain amino acid, this is called the genetic code.

• When mRNA is translated to a sequence of amino acids it is called

The human chromosomes

• The 46 chromosomes in the somatic cells

consists of 22 pairs of autosomes and 1 pair of sex chromosomes.

• The woman has 2 sex chromosomes of the same kind: X, X

• The man has two different kinds of

How is sex determined?

determined by the sex chromosomes.

Social interactions determine the sex

• In the clown fish the dominant

individual in the group turns into a female, the others are male.

• In the cuckoo wrasse (blågylta) the dominant individual turns into a

The human set of chromosomes-

The human set of chromosomes-

The chromosome

• Chromosome that has copied itself (replication) consists of two

identical halves.

Mutations

Two types: Gene mutations and chromosome mutations

• Gene mutations: Occasional errors in one or a few of the nitrogen bases in the DNA sequence.

• Chromosome mutation: Error in the number of

Gene mutations

If one nitrogen base is exchanged by another: • In some cases the changed

triplet does not give any effect on the protein.

• One amino acid is exchanged, the new amino acid works almost as good. No large effect.

Gene mutations

• If one nitrogen base is added or removed the

reading frame will be changed and the effect will be detrimental. The protein will not work at all.

• Ex. YOU ARE NOT THE ONE (understandable words)

YUA REN OTT HEO NE (- one letter)

Cancer

• Relatively often errors occur in the DNA but normally this is “repaired” by killing the

damaged cells.

Chromosome mutations

• Doubling of the chromosome number (in plants)

• One extra chromosome

• One chromosome to few

• Part of a chromosome is missing

Down’s syndrome – trisomy 21

• One extra chromosome number 21 (smallest chromosome in humans)

• Characteristic appearance.

• Different degrees of mental retardation.

• Higher degrees of physical

Turner’s syndrome

• One X-chromosome but no Y-chromosome.

• Due to absence of Y-chromosome the fetus will develop into a girl.

• Short stature.

• Do not develop to women without hormonal treatment.

• Poorly developed ovaries – sterile

Klinefelter’s syndrome

• X,X,Y – one X-chromosome to much.

• Born as boys.

• Low testosterone production.

• Get some female traits (e.g. develop breast)

• Decreased testicular function.