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Chromosome Theory of Inheritance
Genes are located on chromosomes and the behavior of chromosomes during meiosis accounts for inheritance patterns
Exceptions to Mendel's Laws
Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.
Incomplete Dominance
The heterozygous phenotype is somewhere between the two homozygous phenotypes
- Neither allele is completely dominant or recessive
ex: red flower + white flower = pink flower
Codominance
both traits are fully and separately expressed
ex: Red and white flowers make red and white speckled flowers
ex: Blood type (AB; fully A and fully B)
Blood Type
An example of codominance AND multiple alleles
A= I^A I^A or I^A i (anti- B)
B= I^B I^B or I^B i (anti- A)
AB= I^A I^B (none) - universal receiver
O= ii (anti-A and anti-B) - universal donor
Multiple Alleles
Having more than two alleles for one gene
ex: alleles for blood type = A, B, ii
ex: fur color in rabbits
Polygenic Inheritance
A trait produced by two or more genes
- Usually shows a range in phenotype
ex: skin color, eye color, height, personality
- Occasionally epistasis can occur
epistasis
When one gene overshadows all of the others
ex: Labrador retriever fur colors, eye colors, albinism
Polygenic
The Heredity of Complex character that determine by a large number of gas
Linked Genes
genes that are physically located on the same chromosome will be inherited together
ex: blonde hair and blue eyes, red hair and freckles, large ears and broad nose
- Linked genes can only be separated or broken apart during crossing over
ex: the red and blue genes are close together, therefore may be inherited together
Sex-Linked traits
1) Hemophilia - ambos padres
2) Datonismo (color blind) - mamá es el carrier
3) High blood pressure - ambos padres
4) Duchenne muscular dystrophy - mamá es el carrier
5) Fragile x syndrome - mamá o papá
Autosomes
Males and females have exactly the same chromosomes for pairs 1-22
Sex Chromosomes
The last pair of chromosomes that determine the biological sex of the individual
- Females: XX
- Males: XY
Sex-linked genes
genes on sex chromosomes
- If on the X, they are 'X-linked'
X linked genes
Females:
- Inherit x-linked gene as normal and principle of dominance applies
- This is because females have 2 X'S so they inherit two copies of the gene
Males:
- Inherit the gene on the X, but not the Y
- Because they only have 1 X, they express that trait whether it is dominant or recessive, because Y doesn't mask it.
Carrier
Someone who carries the recessive trait but doesn't show it due to having a dominant X to mask it.
Mutation
Any change in DNA; Can occur in ANY cell in the body
Somatic mutations
occur in somatic (body) cells and are passed on by mitosis --> cancer
Germline mutations
occur in the germ line cells that give rise to gametes and are passed on by meiosis --> mutated offspring
What causes mutations?
- Mistakes made during DNA replication, mitosis, meiosis, or protein synthesis
- Mutagens (radiation, UV light, cigarette smoke, etc.)
- Virus
2 Main Types of Mutations
1) Gene mutations
2) Chromosome mutations
Gene mutations
happen during DNA replication and cause a change to the original DNA sequence
ex: cystic fibrosis, dwarfism, and sickle cell anemia
Chromosome mutations
often happen during meiosis, changing the number or location of genes.
ex: Down Syndrome, Klinefelter's Syndrome, Turner's Syndrome
Klinefelter's Syndrome
Born with an EXTRA chromosome - XXY
- short height
- penis, tall structure
- body proportion
Turner's Syndrome
MISSING chromosome - X
- short height
- failure of the ovaries to develop
- heart defects
Point mutations
SUBSTITUTE one nucleotide for another
ex: sickle cell anemia is caused by GAG --> GUG
- Often caused by replication errors or environmental mutagens
Frameshift mutations
the INSERTION or DELETION of a nucleotide
ex: ATTACC --> ATACC (deletion)
ex: ATTACC --> ACTTACC (insertion)
Chromosome Mutations
- Duplication
- Translocation
- Nondisjunction
Duplication
changes the size of chromosomes and results in multiple copies of a single gene.
Translocation
pieces of non-homologous chromosomes exchange segments (during crossing over)
Nondisjunction
chromosomes that do not separate correctly during anaphase, resulting in 1 or 3 chromosomes rather than 2 per cell.
Pedigree
chart used to trace the phenotypes and genotypes in a family to determine whether people carry diseases or traits
Pedigree for an autosomal recessive trait/disease
- Most COMMON inheritance pattern for genetic diseases
- Disease is RARE in the family
- MALES and FEMALES are equally likely to inherit this disease
- Disease often SKIPS generations
ex: Cystic Fibrosis, Sickle Cell Anemia, Phenylketonuria, Tay-Sachs Disease
Sachs Disease
enfermedad en los nervios (usualmente fatal)
Phenylketonuria (PKU)
acumulación de aminoácidos (seizures)
Pedigree for an autosomal dominant trait/disease
- Disease is COMMON in the family (many affected family members)
- MALES and FEMALES are equally likely to inherit this disease
- Disease will NEVER skip a generation (a child cannot inherit the disease if both parents are healthy)
ex: Achondroplasia (a type of dwarfism), Huntington's Disease, Neurofibromatosis
Huntington disease
afecta diréctamente células en el cerebro
Pedigree for a sex-linked recessive trait/disease
- Disease is RARE in the family (only a few affected family members)
- MALES are often MORE AFFECTED than females
- Diseases often SKIPS generations
- Affected fathers DO NOT pass on to their sons
ex: hemophilia, duchene muscular dystrophy, color blind
How to determine the pattern of inheritance in a pedigree
1) If there are way MORE MALES THAN FEMALES AFFECTED --> sex-linked trait
2) Parents (heterozygous/Rr) same shade and child (homozygous recessive/rr) different from them
- If child was shaded: Autosomal Recessive Trait
- If the parents were shaded: Autosomal Dominant Trait
Biotechnology
refers to any technology used to change the genetic makeup of living things to make products
ex: production of antibiotics, vaccines, synthetic hormones, biofuels, food production
Genetic engineering
the direct manipulation of an organism's genome using biotechnology
- the process of replacing genes in an organism in order to ensure that the organism expresses a desired trait.
Recombinant DNA
artificially made DNA from 2 or more different sources
- can only occur when we know where genes occur on specific chromosomes
Genome
an organism's complete set of DNA; all of its genes
Human Genome Project
the first complete map of the entire human genome, completed in 2003
Encode Project
launched as a follow up to the Human Genome Project to interpret the sequence determined from the HGP
1000 Genomes Project
an even more detailed genome map, sequencing over 1000 different people from a variety of ethnic backgrounds, completed in 2015
Gene Maps
show the location of genes on a chromosome
Restriction Enzymes
Used to cut strands of DNA at specific locations (restriction sites)
- Resulting fragments have at least 1 sticky end and can be joined with other DNA fragments by DNA ligase
- Used to create recombinant DNA
Polymerase Chain Reaction (PCR)
-a technique that allows you to copy a piece of DNA without a cell
= DNA Amplification
- Can make many copies of a short DNA sequence in a test tube
Gel Electrophoresis
A laboratory method that uses an electric current to separate DNA fragments based on their molecular size
- Useful for DNA fingerprinting
Personal Genome Sequencing
- Using DNA sequencing technologies to have YOUR personal genome sequence
- This provides information about your physiology and susceptibility to certain diseases
- Could be especially useful for couples who carry genes for genetic disorders to reproduce via IVF
Gene Cloning
produces multiple identical copies of a genes
ex: Recombinant DNA can be inserting into bacteria plasmids. Then when the bacteria reproduces, it makes millions of cells that all contain the cloned gene
Transformation
the process of inserting recombinant DNA into host cells
Gene Therapy
inserting a normal gene (or editing an existing gene) to fix an absent or abnormal gene
CRISPR
a gene editing technique that helps us to understand the genetics behind many diseases
- It doesn't just introduce normal genes, it actually repairs the existing abnormal genes
Stem Cells
undifferentiated cells that have the potential to become anything
- Mostly found in embryos, but can also be found in adult bone marrow
- Can be genetically manipulated and then introduced to replace tissue that is deficient due to disease or damage
Selective Breeding
artificially breeding organisms with a desired trait
pharm
producing pharmaceuticals infarm animals or plants
Genetically modified organisms
organisms altered by recombinant DNA technology for desired traits
ex: GMO
Inbreeding
crossing individuals that are closely related
- can cause health problems
ex: joint tissues in closely bred Labrador retrievers
- Almost all domesticated animals and crops are the result of selective breeding
Hybridization
a type of selective breeding between unrelated organisms
- Occurs between 2 different species
- Offspring are often hardier than either of the parents
Societal Implications
- Better diagnose and treat diseases (and potentially prevent them)
- After affected genes through genes therapy
- Produce pharmaceuticals and pharm animals and plants
- Using microorganisms for environment cleanup
- Forensics
- Agriculture (GMOs)