Complex Inheritance Laws

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 in farm 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)

- Alter affected genes through genes therapy

- Produce pharmaceuticals and pharm animals and plants

- Using microorganisms for environment cleanup

- Forensics

- Agriculture (GMOs)