Organism Number of Chromosomes

Elephant 1260 (630 pairs)

Fern 88 (44 pairs)

Goldfish 94 (47 pairs)

Ascaris 1

Human 4 (2 pairs)

E.coli 46 (23 pairs)

Organisms of the same species will always have the same number of chromosomes

(all humans have 46 chromosomes, just like all goldfish have 94)

Humans have 23 pairs of chromosomes

All somatic (body cells) chromosomes are paired (homologous): One chromosome is from the mother and one chromosome is from the father.

Each chromosome carries many genes

For example, chromosome #1 has over 3000 genes but #22 has around 800

Contains over 240 million base pairs

Contains less--over 800 genes and 80 million base pairs

Genes are sequences of DNA bases that code for a specific product (usually a protein)

Gene mutations- any change in the sequence of bases within a gene.

During DNA replication, mutations can occur if nucleotides are lost, rearrangedor paired in error.

1. Errors in Replication

◦ DNA replication errors are rare…one mistake for every billion nucleotides replicated

◦ This rate is low because DNA repair enzymes constantly proofread and repair errors.

2. Mutagens are environmental influences

such as:

◦ X-rays

◦ UV radiation

◦ Chemicals (ex. cigarette smoke, pesticides – DDT)

◦ Radioactive elements

3. Transposons or “Jumping Genes”

◦ Discovered by Barbara McClintock in the 1950’s, she was awarded a Nobel prize 30 years later (1983)

◦ Make up 50 % of the human genome (80% in corn)

◦ Specific DNA sequences that have the ability to move within and between chromosomes.

3. Transposons or “Jumping Genes”

◦ These genes have their own enzyme built in (transposase) that can cut them out and cut into another DNA sequence, either on the same chromosome or another one.

◦ Their insertion can alter other genes – if they land inside a gene, they can cause a mutation.

◦ However, they can also create genetic diversity by shuffling genes/ creating novel gene products.

◦ Transposons can carry accessory genes, such as antibiotic resistance genes. They can be used to put a gene into the DNA of another organism.

◦ Commonly used as a genetic tool for analysis of gene and protein function.

◦ The number and uses of transposons as molecular tools continues to expand into new fields such as genome sciences and molecular pathogenesis(focuses mainly on the sub-microscopic aspects of disease).

1. Point Mutation – a change in one nucleotide base in the DNA

◦ i) Silent – the same a. a. is still coded for so there is no difference in the protein

◦ ii) Missense – one base change leads to one a.a. change – may or may not be a big problem to the protein

1. Point Mutation

◦ iii) Nonsense – 1 a.a. change leads to a “stop” codon inserted, thus stopping the whole process (protein not made)

◦ iv) Frameshift – an addition or deletion of 1 nucleotide. This changes every codon after the insertion/deletion so changes every a.a.

A karyotype shows the number and appearance of chromosomes in the nucleus. The chromosome micropicture is cut up so that homologous pairs of chromosomes can be arranged together.

Since chromosomes have many genes on them, mutations to a chromosome can affect many genes at once

Occur after chromosomes are broken and reform abnormally

Breaks can be due to radiation, addictive drugs, pesticides etc.

Occur when meiosis “malfunctions”

1. Pieces of chromosomes can be moved

a. Inversion—genes flip spots

b. Translocation—segment of chromosome

moves to another chromosome

2. Pieces of chromosomes can be lost or added

a. Deletion—segment of chromosome removed

b. Duplication—extra copies of genes inserted into chromosome

3. Whole chromosomes can be lost or added

a. Monosomy--# of chromosomes reduced to a single (not paired)

b. Trisomy—Number of chromosomes increased to a triplet

c. Polypoloidy—number of chromosomes increased many times

Occurs in individuals who have 3 sex chromosomes

2 X and one Y

Designated XXY

Infertility

Treated with testosterone therapy

During formation of the egg, both #21’s end up in the egg cell

Upon fertilization, the sperm contains a single #21

Resulting child has three #21’s

Girls with Turner syndrome are born with only one X chromosome

The effects of the condition vary widely among girls with Turner syndrome.

Since changes in DNA can directly affect protein synthesis, this in turn can drastically affect metabolism and body structure and function…leading to some serious genetic disorders

Genetic disorder—a disease or disorder that is inherited geneticallyEx.

Occurs if the enzyme that converts tyrosine to melanin is defective

Will have no skin or hair pigment, so appears almost pure white