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Each pair contains a gene from your mother, and a gene from your father for a particular characteristic
So each pair contains two “options” for a characteristic
These options are called alleles
e.g. gene = eye colour;
alleles = blue eye colour, brown eye colour
An Allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome.
Alleles are dominant or recessive
Homozygous = two same alleles (purebred)
Heterozygous = two different alleles
Dominant + recessive dominant
Dominant + dominant dominant
Recessive + dominant dominant
Recessive + recessive recessive
e.g. BB, Bb = brown eyes; bb = blue eyes
Two parents are Bb + bb; offspring has 50% chance of blue eyes
Trait expressed when 2 traits compete
Trait that expresses itself only when paired with another of the same kind
Underlying genetic material
When genes for characteristics differ
When genes for characteristics are the same
Eye Colour A heterozygous brown-eyed father and a blue-eyed mother: 50:50 chance of being either brown eyed or blue eyed
DOMINANT AND RECESSIVE CHARACTERISTICS Characteristics in the left-hand column dominate over those characteristics listed in the right-hand column . * sex-linked characteristic DOMINANT TRAITS RECESSIVE TRAITS eye coloring brown eyes grey, green, hazel, blue eyes vision farsightedness normal vision normal vision normal vision normal vision nearsightedness night blindness color blindness* hair dark hair non-red hair curly hair widow's peak blonde, light, red hair red hair straight hair normal hairline facial features dimples freckles broad lips no dimples no freckles thin lips
Study of the Effects of Genetics on Behavior
99% of all gene sequences is shared by ALL humans
Genetics produces predispositions
Many personality traits have genetic links: shyness, sociability, moodiness, temperament, assertiveness, depression, AD/HD, schizophrenia
Heredity & Environment
Heredity & Environment Work Together
Genetics is under the influence of the environment
e.g. height, language, & temperament
Interaction of Many Factors
Many traits reflect multifactoral transmission
Determined by a combination of genetic & environmental factors
Question is: How much is nature & how much is nurture?
All data suggests it’s a combination
Physical traits influenced by both genes and environment .
Height is an example: If a child is ill, poorly nourished, or emotionally neglected, s/he may be smaller than others her/his age.
Psychological traits (intelligence, personality) influenced by both nature and nurture (multi-factorial)
Tends to run in families
Monozygotic twins have 50% chance of developing it
Sensitivity to stress
Major depression, alcoholism, autism, AD/HD
Heredity & Environment
Influences of each changes over person’s life-time
GENETIC DISORDERS DOWN SYNDROME
Turner Syndrome Webbed neck – spaced nipples
Prenatal Diagnosis and Treatment
Helps to assess the chances of inherited disorders.
Ultrasound is the use of soundwaves to produce a picture of the fetus.
Amniocentesis allows the taking of a sample of the amniotic fluid.
Chorionic Villus Sampling (CVS) is taken from the placenta and can be done earlier than amniocentesis.
Chorionic Villus Sampling: Done in the first trimester for genetic studies. The cells obtained are identical to those of the fetus, grown and analyzed. Complications include pregnancy loss and limb abnormalities. Done as early as week 5 of pregnancy to detect any genetic disorders Amniocentesis: Amniotic Fluid (20 ml) is withdrawn under US guidance, and is analyzed for prenatal diagnosis of karyotypic abnormalities such as: congenital defects, fetal lung maturity, and NTD. Done at the 14 th -16 th week of pregnancy Complications include pregnancy loss, amniotic fluid leakage, fetal injury This process is indicated for: Women over 35 y. of age: ↑ risk of malformations- 21, 18, 13 trissomy Women who had a child with a chromosomal abnormality.
CHORIONIC VILLUS SAMPLING
Threats to Development
Drugs, chemicals, viruses, etc.
Timing & quantity of the exposure is important
Especially problematic during periods of rapid prenatal development
Poverty increases the chances of exposure
Threats to Development
Developing fetus needs the appropriate nutrients
Under 16, over 30, & over 40 greatest risk
Down’s Syndrome in 1 of 100 over 40 births
Adolescent pregnancies more likely to be premature & still-born
Younger mothers generally have adverse social & economic factors
Rubella prior to 11 th week can produce blindness, deafness, heart defects, or brain damage
2 nd hand smoke affects the mother’s health which affects the fetus
Use of alcohol & illicit drugs can damage sperm
Physical & emotional abuse affects the stress level of the mother
Key points about genetics
Genetic disorders are disorders resulting from defect in the structure or number of genes or chromosomes. Genetics is the study of how and why such disorders occur.
A phenotype is a person’s outward appearance. Genotype refers to the actual gene composition.
A person’s genome is the complete set of genes present.
A karyotype is a graphic representation of the chromosomes that are present.
A person is homozygous if he or she has two like genes for a trait and heterozygous if he or she has two unlike genes for a trait
An important aspect of genetic counseling is respecting a couples right to privacy. Be certain that all information remains confidential.
People who are told that a genetic abnormality does exist in the family may suffer a loss of self- esteem. Offering support to help them deal with the feelings they experience is an important nursing intervention.