It’s in the Genes

Our blueprint for the body

Genes and Chromososmes

• A gene is a unit of hereditary material

• Contains coded information and instructions which direct the development of every cell in the body

• Like a blueprint of how the body will function

A gene is a segment of DNA

• This DNA tells cells how to make a protein

• Proteins are the building blocks of our body

• There are about 100,000 genes in the human body

• Genes are found on thread-like structures, called chromosomes

Chromosome

Chromosomes

• Chromosomes are found in the nucleus of the cell

• They exist in pairs• Humans have 23 chromosome pairs• At the time of conception, each parent

contributes one gene and one chromosome from each of the pairs

• So our cells have 2 copies of each chromosome, one from each parent.

Human Chromosomes

Traits

• Genes and chromosomes from each parent combine to determine which traits the offspring inherits

• At each gene location site on the chromosome, there are two variations of the gene, called alleles

• If they are identical, the individual is homozygous

• If they are different, heterozygous.

More on alleles

• Alleles are either dominant or recessive• The dominant allele in the pair

determines the trait• E.g. Eye color genes. Brown alleles are

dominant over lighter colors. In a pair of alleles with 1 blue and 1 brown, the brown will overshadow the blue and the person will have brown eyes

Punnett Square

• Maps the genes of the parents• Dominant alleles shown by a capital

letter and recessives by a small.• Combinations of the dominant and

recessive genes result in the traits• One trait does not affect another• We will be doing an exercise later with a

Punnet square

Mutations

• Mutations are changes in the gene.• Like a misspelling in the code for a

protein that can be passed from one generation to the next

• Some mutations are not harmful• Some mutant genes function improperly

and cause a disorder, malfunction, or malformation

• E.g. Cystic fibrosis or Marfan’s

Mutations

Some mutations can occur spontaneously and thus can appear for the first time in a family

People have no control over which genes they pass along to their offspring

However, when a person is affected with a genetic disorder that causes illness or disability, they may want to consider whether they pass that gene along.

Congenital Disorders

• Congenital disorders are caused by damage to a developing fetus.

• Can be the result of genetic abnormalities or mutations, the uterine environment or chromosomal abnormalities (Down’s Trisomy 21)

• Congenital disorders are not necessarily genetic.

Types of congenital disorders

• Congenital physical anomaly is an abnormality of the structure of a body part (clinodactaly)

• Congenital malformation is an anomaly that is problematic

• Birth defect is a congenital anomaly evident at birth that is problematic (spina bifida)

• Genetic disorders are all congenital, but may not show until later in life.

• Single, multiple gene or chromosomal defects

Teratogens

• Any agent that can disturb the development of an embryo or fetus.

• A number of medications can cause birth defects (thalidomide was the most famous)

• Alcohol, ACE inhibitirs, sulfas, statins, phenytoin, anti-cancer drugs, radiation

• Avoidance of drugs and alcohol in pegnancy. Smoking not a teratogen, but can cause LBW

• Pregnancy Category Ratings

Dwarfism

• Person of short stature• Can be caused by over 200 medical

conditions• Characteristics of individuals vary widely• Disproportionate: one or more body

parts being large or small in comparison to normal adult humans

• Proportionate dwarfs are small all over

More kinds of dwarfism

• Achondroplasia: 70% of dwarfs.• Bone growth disorder• Short limbs, long trunk, large head

with characteristic facial features• Pituitary dwarfism is caused by a

growth hormone deficiency.