A human has 46 chromosomes normally, 44 of autosomal chromosomes and 2 of sex chromosomes
(male→XY, female→XX)
Generally an autosomal cell is diploid (2n=46), whereas a sex cell (sperm or egg) is haploid (n=23).
○Human inheritance types
Mendelian types
autosomal
dominant
recessive
incomplete dominant
codominant traits
Non-mendelian types
sex-linked inheritance
multifactorail or polygenic inheritance
＜Mendelian types＞
Mendelian types obey the Mendelian lows.
①Low of uniformity
②Low of segregation
③Low of independent assortment
1. Autosomal dominant
AA → disease
Aa → disease
・only homozygous recessive is non-affected (healthy).
aa → healthy
Examples of autosomal dominant diseases
○Huntington disease
・mutation of gene encodes huntingtin protein.
・symptoms; neurodegenerative disorder (involuntary movements, personality changes, dementia)
○Hypercholesterolemia
・mutation of LDL receptor
○Osteogenesis imperfecta
・mutation of collagen
・symptoms; fragile bone, deafness, blue sclera
2. Autosomal recessive
AA → healthy
・ only homozygous recessive is affected (disease)
Aa → healthy
・ most common way of inheritance
aa → disease
Examples of autosomal recessive diseases
○Albinism
・no pigment of eye, hair, skin.
・mutation of tyrosinase enzyme gene (production of melanin is insufficient)
○Sickle cell anemia
・mutation of amino acid sequence in hemoglobin
(glutamate is altered to valine → tertiary structural formation is changed due to less solubility)
・heterozygous advantage is characteristic (recessive allele is resistant to malaria)
○Phenylketonuria
・mutation of phenylalanine hydroxylase enzyme (the enzyme which converts phenylalanine to tyrosine)
○Thalassemia
・mutation of production of one or more peptide chains of globin
3.Imcomplete dominant
Heterozygote shows intermediate between the dominant phenotype and recessive phenotype.
Example; the color of sweet peas
Dominant allele [A]; Purple
Recessive allele [a]; White
Heterozygote Aa; Purple, white, light purple
4. Codominant
One or more than one traits show dominance to one trait.
Example; ABO blood group
A and B are equally dominant to O
＜Non-Mendelian types＞
1. Sex-linked inheritance
・the trait which is inherited to offspring is on the sex chromosome (mostly on the X chromosome)
・in female, 1 X chromosome is carried by her mother another is carried by her father.
・in male, X chromosome is carried by his mother Y chromosome is carried by his father.
(1)X-linked dominant
Female
Male
XAXA → disease
XAXa → disease
XaXa → healthy
XAY → disease
XaY → healthy
Examples of X-linked dominant diseases
○Amelogenesis imperfecta
・abnormal formation of enamel
○Familial hypophosphatemic rickets
・decreased reabsorption of phosphate by renal tubule
○Fragile X syndrome
・mental disorder
(2)X-linked recessive
Female
Male
XAXA → healthy
XAXa → healthy
XaXa → disease
XAY → healthy
XaY → disease
Examples of X-linked recessive diseases
○Color blindness
○Hemophilia
○Duchenne muscular dystrophy (weakening of muscles)
・The incidence of X-linked inherited disease is much greater in males than in females because;
・female has 2 X chromosomes. (especially in the case of X-linked recessive)
・Dosage compensation (especially in the case of X-linked dominant)
→One X chromosome is inactivated randomly in early embryo and an inactivated X chromosome is
seen as a Borr body near the cell membrane.
(3)Y-linked inheritance
・Only male is affected (affected father transmits disease 100% to his son)
2. multifactoral or polygenic inheritance
・one phenotype is regulated or interacted by several genes and environmental factors
(1)Gene interaction
①collaboration (cooperation)
2 genes work together to produce a new phenotype. Ex. walnut comb of chicken
②epistasis
Ex. color of Labrador retriever (1allele gives color, another gives color precursor)
③additive effect
(2)Polygenic inheritance
Skin color, body height, etc.
due to additive gene interaction, incomplete dominance and environmental factors, etc.
※Sex-influenced trait
Ex. Baldness
・autosomal dominant in males, but autosomal recessive in females
○Chromosomal mutations or aberrations
1. Structural
(1)Translocation
・a chromosome fragment breaks off and attaches to a non homologous chromosome
・in reciprocal translocation(most common type of translocation),
2 non homologous chromosome exchange parts.
Example;
○Philadelphia chromosome・・・example of reciprocal translocation
○Translocational down syndrome・・・example of Robertsonian translocation
・have one chromosome 14, one combined 14/21 chromosome, and two normal copies of chromosome 21
・the large arm of chromosome 21 has been translocated to the large arm of chromosome 14
・all or part of the genetic material from chromosome 21 is thus present in triplicate
(2)Deletion
・part of a chromosome is missing
Example;
○Cri du chat syndrome
・part of the short arm of chromosome 5 is deleted
・symptoms; small head, moon face, cry sounds like a kitten mewing, mental retardation
(3)Inversion
(4)Insertion with translocation
(5)Ring chromosome
(6)Isochromosome
(7)Duplication
2. Numerical
(1)Polyploidy.
・the presence of multiple sets of chromosomes
・lethal in human
(2)Aneuploidy
・the presence of a single extra chromosome(trisomy), or the absence of a chromosome(monosomy)
・result of nondisjunction(abnormal meiotic division in which chromosomes fail to separate)
①Monosomy
○Turner syndrome
・has only 1 X chromosome [XO]
・develops as a female, but internal and external genital structures are underdeveloped → sterile
・no Borr body
②Trisomy
・autosomal
○Down syndrome・・・trisomy of chromosome 21( abnormal physical and mental development)
○Edwards syndrome・・trisomy of chromosome 18
○Patau syndrome・・・trisomy of chromosome 13
・gonosomal
○Kleinefelter syndrome・・trisomy of X chromosome in male [XXY] has 1 Borr body
○Super male (XYY syndrome)・・trisomy of Y chromosome in male
○Super female (XXX or triple X syndrome)・・trisomy of X chromosome in female
○Viruses
1. Structure
capsid (protein coat) ＋
nucleic acid (DNA or RNA)
2. Bacteriophage・・host cell is bacteria
life cycle
① lytic cycle (virulent bacteriophage)
・break down the DNA of host bacterium and bacterium itself as well
②lysogenic cycle (template bacteriophage)
・the genetic material of phage is inserted to the DNA of host bacterium and transmitted to next
generations
・If there is a certain stimulus they turn into lytic cycle
3. Way of getting into host
・membrane fusion
・endocytosis
4. Major diseases caused by viruses
・AIDS: caused by HIV (example of retrovirus)
・Hepatitis B, C: caused by hepatitis viruses
・Herpes: caused by herpes virus
・Influenza: caused by influenza viruses
○Bacteria
1. Structure
・bacteria are prokaryote (circular DNA, no endomembrane system)
・cell wall: prevent from bursting in hypotonic condition, consists of sugars attached by peptides
Gram positive bacteria・・thick cell wall
Gram negative bacteria・・thin cell wall + outer membrane outside the cell wall
・capsule: jelly like substance
・pilus and flagellum
・plasmids
2. Reproduction
(1)Asexual; genetically equal
①clones
②binary fission
③budding
④fragmentation
(2)Sexual; genetically different
①transformation (from environment)
②transduction (occurred by bacteriophage)
③conjugation (occurred by transmitting or accepting plasmid)
3. endospore
Not for reproduction but dormant form of bacteria
Resistant to environmental changes
4. Metabolism
(1)Autotrophs
・synthesize organic compounds from inorganic compounds by photosynthesis or chemosynthesis
(2)Heterotrophs
・organic sources from other organisms
①Saprotrophs ; their carbon source is dead body of other organisms
②Parasites ; their carbon source is living organisms
5. Respiration
(1)Aerobic
(2)Anaerobic
Facultative anaerobe: aerobic ＋ anaerobic (tolerate Oxygen) Ex. yeast
Obligate anaerobe: aerobic only (oxygen is poison for them)
Ex. tetanus bacteria