Bio Unit Test 2 - Genetics

DNA

deoxyribonucleic acid

• serves as the instruction manual for a cell; what to do, when to do and how to do it

Macromolecules

(made up of monomers)

• carbohydrates

• proteins

• lipids

• nucleic acid

Shape of DNA

Double Helix

Nitrogenous Bases

• Guanine (G) bonds to Cytosine (C)

• Adenine (A) bonds to Thymine (T)

Each DNA molecule is made up of thousands of nucleotides

• 1 nucleotide = 1 phosphate + 1 sugar + 1 nitrogen base

Histone

a positively charged protein that DNA wraps around

• NOTE** DNA has a negative charge

Nucleosome

A complex (package) of eight histones

• Each histone in the complex is wrapped in DNA

Chromatin

A larger structure of nucleosomes

Chromosome

A single package of supercoiled DNA

• One chromosome is a single strand of DNA that is wrapped around histones

Organization of DNNA from general to specific

DNA double helix

DNA wrapped histone

Nucleosome

Chromatin (thin usually)

(mitosis + meiosis) Supercoiled Chromosome

Gene

Alleles

What are haploid sperm cells called?

spermatozoa or singular spermatozoan

The process to create sperm cells

Spermatogenesis

Spermatogenesis begins with a diploid germ cell called a…

spermatogonium

The process of generating haploid egg cells:

Oogenesis

Oogenesis begins with a diploid germ cell called an…

oogonium

Unequal division of the cytoplasm in oogenesis results in..

• unequal division of the cytoplasm

• Thus, one gamete is larger than the others - the primary oocyte

• The smaller cells are called polar bodies

• This results in one viable egg cell

Why is the viable egg cell (or primary oocyte) larger than the polar bodies?

• The viable cell has more cytoplasm to that after fertilization it can survive the travel to the uterus for implantation

Non-disjunction

failure of chromosomes to separate properly during meiosis

• This results in the addition or deletion of one or more genes from a gamete

If non-disjunction occurs in Anaphase 1:

• Homologous chromosomes do not separate

• Two gamete have an extra chromosome and two gametes lack one chromosome

If non-disjunction occurs in Anaphase 2:

• Sister chromatids are not properly separated

• Two gametes have normal number of chromosomes, one gamete has an extra chromosome and the fourth gamete lacks one chromosome

Trisomy

when an organism has three copies of a chromosome

• In humans, a third copy of chromosome 21 is known as Down’s Syndrome

Mutation

a permanent alteration in the DNA sequence that makes up a gene

• A mutation can have a positive, negative or neutral effect on an organism

As the cell with the mutation replicates…

the mutation is also replicated

Mutations can be caused by…

1. An error during DNA replication

2. A mutagen - a substance that causes mutation

• E.g. radiation, viruses, or toxic chemicals

Germ line mutation

• the mutation occurred in a sex cell and can be passed onto offspring

Somatic mutation

• the mutation occurred in a somatic cell and cannot be passed onto offspring

Gene mutation

Changes in one gene

Chromosome mutation

leads to changes in an entire chromosome

The 3 different types of mutations

1. Insertion

2. Deletion

3. Duplication

Insertion

changes the number of DNA bases in a gene by adding a piece of DNA

Deletion

A deletion changes the number of DNA bases by removing a piece of DNA

• Small deletions may remove one or a few base pairs within a gene, while larger deletions can remove an entire gene and/or several neighboring genes

Duplication

A duplication consists of a piece of DNA that is abnormally replicated one or more times

The Genetic Code

DNA → transcription → RNA → translation → Protein

• DNA codes for the information to make RNA

• RNA codes for the information make protein

Codon

3 bases that code for an amino acid

Autosome

 Any chromosome that isn’t a sex chromosome

What chromosome is the sex chromosome?

chromosome 23

Syndrome where there is 3 X chromosomes

Tay-Sachs syndrome

3 Copies of chromosome 21

Down’s Syndrome

Prenatal Testing

:Tests performed on a fetus (a developing baby still in the womb) that are based on testing for genetic abnormalities

Non-invasive tests

• Fetal proteins in the expectant mother’s bloodstream are analyzed and an image of the fetus and measurements of fluid at the back of the fetus’s neck are obtained

• These are non-invasive because the DNA of the fetus does not need to be sampled

The 2 Types of invasive prenatal tests:

1. Amniocentesis

2. Chorionic villus sampling

Amniocentesis

• A sample of amniotic fluid (fluid surrounding the fetus), which contains fetal cells is taken after the 14th week of pregnancy

Chorionic villus sampling

• A sample of cells from the chorion (part of the placenta) is taken after the 9th week of pregnancy

• In these tests chromosomal abnormalities, genetic disorders, and certain malformations of the brain and spine are monitored

Selective Breeding

• the controlled breeding of plants and animals with specific combinations of useful or desirable traits.

• Often imprecise because it combines many genes (thus many traits) at a time

• Many reproductive technologies are used now to help with this selective process

Artificial Insemination

the artificial transfer of semen into a female’s reproductive tract

• Typically, the semen is processed and stored prior to introduction

Why do farmers use artificial insemination?

• Makes semen from high-quality males more widely available (through breeders and on-line sources)

• Allows farmers and/or pet owners to choose desirable traits for the male parent

Embryo Transfer

• fertilizing an egg artificially and then transferring it into a recipient female

• Can be coupled with modern genetic techniques to ensure the quality of the embryos that are being implanted

How is embryo transfer a technique more likely to ensure the female gets fertilized by the male that farmers want?

Because farmers can choose a high-quality male parent with desirable traits to ensure that the resulting offspring has a better chance of having those desired traits. This technique allows for more control and efficiency than natural breeding.

In Vitro Fertilization (IVF)

• the technique used to fertilize egg cells outside the female’s body; a solution for women who have blocked Fallopian tubes

• Most common and effective type of assisted reproductive technology

• Louise Brown was the first baby born through IVF

IVF is used when:

• a person is unable to get pregnant naturally

• a person or couple is diagnosed with unexplained infertility

• male factor infertility or abnormal sperm parameters

• a person’s fallopian tubes are blocked

The IVF process consists of:

1. Superovulation

2. Retrieving the eggs

3. Insemination, fertilization, and embryo culture

4. Embryo transfer

Why has IVF led to more fraternal twins than in the past?

Often multiple embryos are fertilized and inserted back into the woman’s uterus to increase the chances of a successful pregnancy however if two embryos are successful they will become fraternal twins.

Preimplantation Genetic Diagnosis (PGD)

• Diagnosis of genetic disorders soon after fertilization, with IVF used in these cases

• Once IVF is performed, zygotes are allowed to divide over two days, and then one cell from each of the developing embryos is analyzed for the presence of a genetic disorder. After the genetic analysis, only the healthy embryos are implanted in the female’s uterus.

Common use of PGD

• Parents of sick children have used PGD to create a genetic match in another sibling

  • As a genetic match the newborn sibling is able to donate umbilical cord blood, which contains stem cells that can be used to treat a number of diseases.

Gene Cloning

• manipulating DNA to produce multiple copies of a gene or another segment of DNA in foreign cells. 

• The cloned DNA can be used for further study, or for mass production of the protein that the gene codes for.

Application of Gene Cloning

•  insulin, a hormone that enables the body to use sugar, is absent in people diagnosed with type I diabetes. Before gene cloning, people with diabetes used purified insulin from animal sources which was a labour-intensive procedure that made insulin expensive to produce. Now human insulin is produced in bacteria through cloning of the insulin gene.

Therapeutic Cloning

• the process of replacing an egg cell’s nucleus with the nucleus from a somatic donor cell to produce a cell line of genetically identical cells through a process called somatic cell nuclear transfer (SCNT)

• These are used to treat various diseases

  • This includes using the cloned cells to grow new tissues and organs

• Cells produced by SCNT are stem cells

Stem Cells

• an undifferentiated cell that can develop and become specialized into different cell types of the body.

• If human cells produced through SCNT are implanted into a surrogate, they could develop into an embryo and produce a human clone.

• Now that scientists can use pluripotent stem cells, their reliance on embryonic tissue will be reduced or eliminated.

The key to stem cell research is learning how to “program” stem cells to become certain cell types

Applications of Stem Cells

• improving heart function and formation of blood vessels by injecting stem cells into the circulatory systems of animals.

• “Growing” blood vessels, heart valves, skin, and a urinary bladder in the lab.

– holds great promise for regenerative medicine (tissues and organs to replace those damaged or lost due to age, disease, trauma, or genetic defects)

• Since made from the patient’s own stem cells they are a genetic match and won’t be rejected by the immune system

Reproductive Cloning

• the process of producing genetically identical organisms through somatic cell nuclear transfer (SCNT)

• One potential application is to use reproductive cloning to repopulate an endangered species

Cons of Reproductive Cloning

• Usually unsuccessful (birth rate ranges from 0.5% - 6%)

  • High mortality rate

  • High incidences of disease and premature aging

Transgenic Organisms

• organisms whose genetic material includes DNA from a different species. Transgenic organisms are a type of genetically modified organism, or GMO. 

GMO

an organism that has had the sequence of its genome altered for a specific purpose.

Applications of Transgenic Organisms

• increased resistance to herbicides, insect pests, or viruses

• increased nutritional value

• A medical application example is the safflower plant which had the human insulin gene inserted into it so that it produces insulin as it grows

• A spider gene has also been inserted into goats that makes them secrete spider silk in their milk which is supposed to be spun into lightweight & strong fibres that have practical uses such as clothing and nets

Hippocrates

• Greek philosopher 

• Theorized that every part of the body contributed to the making of the “seeds” of the parents 

• The seeds fused together to give rise to a new individual 

Aristotle

• Believed that male and female semen mixed together at conception 

William Harvey

• A physician 

• Proposed the theory of Epigenesis -- the embryo develops in stages

• The development is affected by factors that are inside and outside of the mother 

Anton van Leeuwenhoek

• Used microscope to examine the gametes of humans and other organisms 

• Discovered “animalcules” in the semen of organisms  

• He believed that the animalcules contained pre-formed embryos 

• Women did not make any reproductive contribution except for providing a place (the uterus) for the embryo to develop 

Pangenesis

• Proposed by the Greeks, supported by Charles Darwin 

• Males and females formed “genes” in every organ 

• The genes moved through the blood, to the genitals and then into children 

• This thought was influential in biology until a little over 100 years ago 

• Disproved by Francis Galton 

Blending Theory

• Popular during the 19th century

• Sperm and egg mix together resulting in offspring whose traits are a blend of their parent’s characteristics 

• e.g. The offspring of a red plant and a white plant would be pink – note, this was not always the case 

• This theory was not applicable to all inheritance patterns

Charles Darwin

• Theorized that offspring were variations of their parents’ characteristics 

• Could not explain how this happened 

Who is the Father of Genetics

Gregor Mendel - Austrian Monk who studied Biology, Chem, Physics & Math

Why was using the common pea plant to carry out his studies a good choice for Mendel?

• Pea plants can self-pollinate and cross-pollinate

• Different varieties of pea plants expressed different traits

• For each trait there were only two possibilities (e.g. height → tall or short)

Mendel’s Major Conclusions

1. The Particulate Theory

2. The Principle of Dominance

3. The Law of Segregation

4. The Law of Independent Assortment

The Particulate Theory

The carriers of inherited traits are present in indiscrete units that retain their integrity in the presence of other units

The Principle of Dominance

• When individuals of contrasting traits are crossed, the offspring will only express the dominant trait

• Therefore, if tallness is dominant, and shortness is recessive, when individual plants bearing these traits are crossed, the offspring will express tallness

The Law of Segregation

• Inherited traits are determined by pairs of factors (alleles) 

• These factors segregate from one another during the formation of gametes

The Law of Independent Assortment

• During the formation of gametes, different pairs of alleles are segregated independently to other alleles

• In other words: The inheritance of alleles for one trait does not affect the inheritance of alleles for another trait

** this is only true for genes on separate chromosomes

Continuous Variation

Traits for which the phenotypes vary gradually from one extreme to another

Ex. height & skin colour in humans

Traits that are controlled by many genes are called…

Polygenic traits

• A group of genes that all contribute to the same trait

• Each dominant allele contributes to the trait

• Recessive alleles do NOT contribute

• For skin colour, the more dominant alleles, the darker the skin colour of the individual

How is Sickle Cell anemia inherited?

Autosomal recessive pattern

Symptoms of Sickle cell anemia

• low number of red blood cells

• repeated infections

• periodic episodes of pain

**Severity of these symptoms can range from mild to severe (hospitalization)

• Anemia (fatigue, shortness of breath, delayed growth & development(

• Yellowing of skin and eyes

How is Beta-Thalassemia inherited?

Autosomal recessive pattern

Symptoms of Beta-Thalassemia

• increased risk of developing abnormal blood clots

• Major life threatening anemia in developing anemia within the first 2 years of age. This can cause their bodies to not grow and develop at a normal level, and may cause them to develop jaundice

• Anemia, which has its own symptoms of fatigue, weakness, pale skin colour, etc.

• Enlarged spleen, liver, and heart

• Misshapen bones

• Delayed puberty

• frequent blood transfusions needed

How is Cystic Fibrosis inherited?

Autosomal recessive pattern (both copies of the gene in each cell need to have the mutation)

Symptoms of Cystic Fibrosis

• Mucus in airways trap germs and dust in the body

• The excess buildup of mucus in the pancreas doesn’t allow for the production of digestive enzymes causing malnutrition and poor growth

• Mucus can block the bile duct, which causes liver disease

• In men, CF can alter the fertility, causing an inability to have children

• Salty-tasting skin

• Persistent coughing, + phlegm

• Frequent lung infections (such as pneumonia and bronchitis)

• Wheezing/shortness of breath

• Poor growth or weight gain despite good appetite

• Frequent greasy & bulky stools, or other difficulties with bowel movements

• Nasal polyp

How is Opitz-Kaveggia (FG Syndrome) inherited?

X-linked recessive pattern

Symptoms of Opitz-Kaveggia (FG Syndrome)

• poor muscle tone (hypotonia)

• intellectual disability

• constipation

• other anal anomalies

• complete or partial absence of the corpus callosum

• broad thumbs

• wide big toes

• small ears

• tall and prominent forehead

• down slanting eyes

How is Cri du chat syndrome inherited?

Not inherited, occurs when a piece of chromosome 5 is missing.

Symptoms of cri-du-chat syndrome

• high-pitched cry that sounds like a cat

• intellectual disability

• small head size (microcephaly)

• low birth weight

• weight muscle tone (hypotonia) in infancy

• widely set eyes

• low-set ears

• small jaw

• rounded face

• some children with this syndrome are born with a heart defect

How is Huntington’s disorder inherited?

Autosomal dominant pattern

Symptoms of Huntington’s disorder

• difficulty concentrating and memory lapses

• depression

• stumbling and clumsiness

• involuntary jerking or fidgety movements of the limbs and body

• mood swings and personality changes

• problems swallowing, breathing, and speaking

• difficulty moving

How is Down’s Syndrome inherited?

Not inherited, happens randomly because of an error in cell division called nondisjunction, which results in trisomy (three copies) of chromosome 21

Symptoms of Down’s syndrome

• intellectual disability

• underactive thyroid gland

• delayed development

• behavioral problems

characteristic facial appearance:

• flattened face

• small ears

• short neck

• upslanting eyes

• tongue that sticks out of mouth

Increased risk of developing several medical conditions such as:

• gastroesophageal reflux

• celiac disease

Pedigrees: Autosomal Dominant

• Each affected person should have at least 1 affected parent

• Males & Females are equally affected

• An affected person has at least a 50% chance of passing on the dominant trait to offspring

Pedigrees: Autosomal Recessive

• An affected person may not have affected parents. This means that the parents would be carriers

• Affects both sexes equally

• Can appear to skip generations

• Two affected parents will have affected children 100% of the time

Pedigrees: X-linked Recessive

• Females can be carriers (heterozygous)

• Can appear to skip generations

• Two affected parents will have affected children 100% of the time

• An affected male will never produce an affected male offspring, but can produce a carrier or affected female

What is CRISPR used for in a laboratory setting?

It is used for editing genomes - which has applications like correcting genetic defects, modifying crops, preventing the spread of disease, etc.

What does CRISPR stand for?

Clusters of regularly interspaced short palindrome repeats

In what organisms are CRISPR found?

Bacteria and archaea