Biology

Human Genetics

Info within the Nucleus Genome: complete set of genetic info in an organism (or

group of organisms).

DNA wraps around proteins called histones; this allows the coiling (or condensing) of DNA within the nucleus.

Humans have 46 chromosomes in every cell (except RBCs & gametes).

Human genome contains ~3 billion bases.

http://www.google.com/imgres

The Human Genome Project:

This is the sequencing of all of the DNA of humans (as well as other organisms)

This begun in 1988 and ended in 2000.

They originally thought there were 90,000 genes but there are only about 25,000-30,000 genes.

The goal was to sequence all genes for both normal and abnormal functions (normal and diseased genes).

Project’s Goal:

To use this information for in the fields of genetic engineering (the use of biotechnology, using biochemical techniques to identify, study and modify genes).

(The hope is to gain understanding in) genetic therapy (medical treatments that attempt to change a genome with the use of genetic engineering).

Other organisms’ genomes have also been sequenced: mice, cats, dogs, fruit fly (Drosophila), yeast, Escherichia coli (bacteria), Helicobacter pylori (ulcer causing bacteria), and some viruses (not living).

The Human Gene Map

A karyotype is a chart of chromosomes that scientists use to study the differences in chromosome shape, structure & size.

In humans, doctors use karyotypes to determine the baby’s genetic sex & to see if there is an abnormal chromosomal # or chromosomal abnormalities.

http://www.miscarriage.com.au/images/pages/karyotype_normal.jpg http://www.slh.wisc.edu/outreach/images/genetics/karyotype.gif

Chromosomal Abnormalities: Chromosomal Abnormalities show on karyotypes.

They can be too many or too few chromosomes.

This is the result of chromosome pairs not separating in meiosis: during anaphase I in meiosis I or during anaphase II in meiosis II.

This is called nondisjunction, meaning not separating.

http://embryology.med.unsw.edu.au/Defect/images/trisomy21female.jpg

Nondisjunction:

1 daughter cell receives an extra copy of a chromosome while another daughter cell does not receive a copy of the chromosome Result = gametes have an abnormal amount of

chromosomes (or genetic material).

If this gamete joins with another, the resulting offspring will be abnormal if it survives.

A monosomy is when a zygote has 1 less chromosome (2n-1, or 45 chromosomes).

A trisomy is when a zygote has 1 extra chromosome (2n + 1, or 47 chromosomes)

Very few monosomies or trisomies in humans survive. Some that survive are:

Down Syndrome is trisomy 21 (3 chromosome #21).

The sex chromosomes tolerate far more manipulations. Trisomy X (XXX) or XXY survives as well

as monosomy X (Xo) survives.

http://www.nacdbookstore.com/images/down-syndrome.jpg

A polyploidy is the result of a complete set of chromosomes not separating.

In animals, the organism generally does not survive but in plants, a hardy plant is produced. In general, the best characteristics of both parents

are taken and the plants are healthier and stronger.

25-50% of ALL plants are polyploids.

This includes wheat used to make bread, potatoes, oats, bananas, peanuts, barley, plums, apples, sugar-cane, coffee, & cotton.

Gene Mutations:

These may involve single nucleotides or small sections of DNA.

These include Frameshift mutations, Point mutations, and Jumping genes

1. Frameshift Mutations:

The addition or deletion of nucleotides that alters the sequence of bases (or reading frame).

http://www.google.com/imgres

2. Point Mutations:

Result in substitution of only 1 nucleotide that only affects 1 codon.

may affect affect 1 a.a.

About 30% of point mutations produce no changes in proteins. These are called silent mutations.

http://www.google.com/imgres

3. Jumping Genes: Insertions of larges

stretches of DNA into the gene.

Barbara McClintock (1947), an American geneticist studying corn, discovered these.

Jumping genes are called transposons

http://www.google.com/imgres

Damaged Chromosomes:

Deletions: when pieces of chromosomes are removed

http://images1.clinicaltools.com/images/gene/5_deletion_large.jpg

Damaged Chromosomes:

Duplications: when fragment of the deleted chromosome attaches to the homologous chromosome, resulting in extra copies of genes

http://images2.wikia.nocookie.net/psychology/images/thumb/1/1d/Chromosome_duplication.jpg/220px-Chromosome_duplication.jpg

Damaged Chromosomes:

Inversion: when fragment of deleted chromosome attaches to original chromosome but upside down

http://www.web-books.com/MoBio/Free/images/Ch8E2.gif

Damaged Chromosomes:

Translocation: when fragment of deleted chromosome attaches to nonhomologous chromosome.

http://members.cox.net/amgough/mutation_chromosome_translocation.gif

Predictions & People: Pedigree Studies:

Human studies are not as easy to study like pea plants. WHY? Generations are slow, humans reproduce too slowly, humans

have few offspring and genetic studies on humans can be unethical.

A pedigree is a chart that shows how a trait and the gene that controls it are inherited within a family.

Key: A circle =female; a square = male Shaded =has the trait; ½ shaded =carrier of the trait;

horizontal line between male & female =marriage line; Roman numerals =indicate generations; Arabic numerals =individuals within generations

Pedigree Key:

http://dbs.umt.edu/courses/biol101S04/labs/Wyrick_s04/14_human_pedigree_analysis_files/image002.gif

http://www.uic.edu/classes/bms/bms655/gfx/pedigree1.gif

Genetic Counseling:

A genetic counselor is a person who provides information about probabilities of offspring and genetic disorders.

They use pedigrees, Punnett squares & genetic tests.

They explain probabilities and possibilities.

If the people they are counseling are pregnant, they also give options and possibly more tests that may determine, for example, if the child has Down Syndrome (an extra chromosome).

PKU, or phenylketonuria, is a genetic disease that is tested for on newborn babies in the US.

A person with this disease lacks the enzyme to break down phenylalanine (an amino acid found in many food products, like milk and gum).

If a person eats this, phenylalanine builds up & causes developmental disabilities and eventually death.

The treatment is to avoid phenylalanine.

Diseases:

It takes 2 recessive alleles to reveal a recessive disease or trait (otherwise the trait or disease will “hide” behind the dominant allele and the person is a carrier).

1. Tay-Sachs Disease is a disease in which a person cannot break down lipids. They accumulate in the brain

and this results in blindness & brain damage.

Eventually, death occurs.

http://www.google.com/imgres

2. Cystic Fibrosis (found on chromosome #7) is a disease that results in excessive secretions of mucus which accumulates in the digestive tract & lungs.

http://www.google.com/imgres

3. Albinism has various forms that is the result of lack of pigment. A true albino lacks

skin pigment. Other forms have

pale skin and white-blond hair.

Albinism affects all races and animals.

http://www.google.com/imgres

Dominant Traits:

Some dominant traits are: freckles, widow’s peak, far-

sightedness, and polydactylly (extra fingers & toes).

http://oneparticularwave.files.wordpress.com/2006/04/517px-Polydactyly_01_Rhand_AP.jpg

http://www.google.com/imgreshttp://www.google.com/imgres

Dominant Diseases:

Achondroplasia (dwarfism)

Individuals are heterozygous (homozygous = fatal)

http://www.google.com/imgres

Dominant Diseases:

Huntington disease. (results in the deterioration of the nervous system which develops in the late 30’s or early 40’s)

There is a genetic test that can be performed to determine if one will develop this disease.

Found on chromosome #4

http://www.google.com/imgres

Genetic Cancers Growth factors: proteins that initiate cell division

Tumor-suppressor genes: make proteins that stop cell division (prevent cancer)

When mutations accumulate to genes that regulate control of the cell cycle, tumors (possibly cancer) may develop.

Oncogenes: cancer-causing genes

http://www.google.com/imgres

Technically, cancer is “genetic” b/c it results from a mutation in the DNA.

However, The REALITY is: inherited mutations that cause cancer (inherited cancer genes) ONLY result in a higher risk of cancer. If inherited it does not mean the person WILL get cancer. Ex: BRCA1 (mutated

tumor-suppressor gene for breast cancer)

http://www.google.com/imgres