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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.