Inheritance of Traits
Pedigrees
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A pedigree is a diagram that shows how a trait is inherited over several generations
o Squares stand for males and circles stand for females
o A filled symbol means that person has the trait or condition
o An empty symbol means that person does not have that trait or condition
o A horizontal line joining a male and female indicates mating
o A vertical line indicates offspring arranged from left to right in order of their
birth
Genetic Traits and Disorders
Genetic disorders are diseases or disabling conditions that have a genetic basis
Polygenic inheritance are traits that are influenced by several genes.
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Examples:
o skin color is affected by 3-6 genes,
o eye color
o height
o hair color
Complex characters are traits that are influenced by both the environment and by genes
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Examples:
o Skin color is affected the sun and genes
o Height is affected by nutrition, sleep, disease , and genes
Multiple Alleles - genes that have more than three alleles for a trait
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Examples:
o Blood typing: ABO blood groups can lead to type A, type B, type AB, and type O
bloods
Adult humans have 4-6 liters of blood in the body
Red blood cells
o Contain hemoglobin, a protein that binds oxygen
o They transport oxygen to the body tissues and remove carbon dioxide from
them
White blood cells fight infection
Platelets help blood clot
Plasma is the fluid that contains salts and protein and the red and white blood cells
Incomplete dominance occurs when one allele is slightly dominant over another and the result
is a phenotype in between the parents
 Example: Curly hair is dominant to straight hair and a cross between these two people
would result in wavy hair
X-linked traits are found on genes located only on the X chromosome
 A male inherits his X chromosome from his mother
 There are several X linked recessive disorders
o Examples
 Colorblindness
 Muscular dystrophy
 Scaly skin
 Hemophilia
 Since it is a recessive disorder females would need to have 2 alleles for the disorder, but
since males only have one X chromosome they will get the disorder if mom gives it to
them.
o Examples of hemophilia in males and females
 XHXH Mom would be normal
 XHXh Mom would be a carrier
 XhXh Mom has colorblindness
 XHY Dad is normal
 XhY Dad is colorblind
Sex influenced traits
 Males and females can show different phenotypes even when they share the same
genotype.
 Sex influenced traits are usually autosomal
 Example: Pattern baldness
o It is an allele that is dominant in males but recessive in females
o The difference is due to the high levels of testosterone in men and lower levels
in women
o The hormone interacts with the genotype to produce pattern baldness
Single allele traits
 A single allele of a gene controls single allele traits.
 There are more than 200 human traits governed by single dominant alleles
 Huntington’s disease is an autosomal dominant condition characterized by
forgetfulness and irritability
o It develops when a person reaches 30-40 years of age
o It progresses to muscle spasms, severe mental illness, and finally death within a
few years.
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Each affected person has at least one affected parent
Unfortunately HD patients have already had children by the time their
symptoms appear
DNA testing can reveal the disorder and people are now getting tested if they
know their parent had it.
Detecting Genetic Disease
 Many people with a family history of genetic disease seek genetic screening before
having children
 Examples of genetic screening include
o Karyotypes provide pictures of the chromosome to show chromosome numbers
and the ability to see if the chromosome is misshapen
o Blood tests for certain proteins which are produced with different disorders
o Direct DNA testing
 Amniocentesis allows physicians to remove some amniotic fluid from
the amnion, the sac that surrounds the fetus between the 14th and 16th
week of pregnancy. Geneticists can analyze fetal cells for genetic
disease by examining chromosomes and proteins in the cell
 Chorionic villi sampling
 Physicians take samples of the chorionic villi, cells that grow
between the mother’s uterus and the placenta…samples can be
taken between the 8th and 10th week
 The test allows physicians to analyze fetal cells, chromosomes,
proteins and detect genetic disease
o Genetic Counseling is the process of informing a person or couple about their
genetic makeup
 It informs individuals about problems that might affect their offspring
 It teaches families how to lower risk factors in their offspring, especially
if there are environmental factors that can affect them
Treating Genetic Disease
 Sometimes only the symptoms can be treated
o Example: PKU is a genetic disease where the individual cannot process the
amino acid phenylalanine
 Doctors test babies a few days after birth
 If the child has it they must eliminate phenylalanine from the diet
 If undetected it causes severe mental retardation
 Gene therapy involves replacing the defective gene
o Sometimes they are able to do this by introducing the functional gene in a
number of ways.