Week 1 Quiz Notes: Three Parent Babies

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THREE PARENT BABY- Summary and Quiz Review

Baby born with DNA from three people (mother, father, donor)

This medical procedure allows parents with rare genetic mutation to have healthy babies

Legally approved in the UK only

Procedure carried out by American doctor in Mexico

Mother had fatal genetic disorder (Leigh Syndrome)

Leigh syndrome: fatal genetic disorder that affects the mitochondrial DNA that is passed down from the mother only

previously, both her children died because of her disorder

Used spindle nuclear transfer to remove nucleus from the affected mother

Spindle Nuclear Transfer:

The mother's original egg, with the affected mitochondrial DNA, has its nucleus removed.

The donor's egg, which her egg is previously removed, is used as the mother's nucleus is inserted into her egg.

The father's sperm is used to fertilize the child and it is born with three parents.

The donor's mitochondria are used and there is no Leigh syndrome. There are health risks and ethical concerns, though.

Genetic Principles exemplified by Three-Parent Baby

Fertilization: The fusion of gametes to initiate the development of a new individual organism. Two haploid gametes to make a diploid zygote.

Haploid: A cell or nucleus having a single set of unpaired chromosomes.

Diploid: Two haploid gametes come together to make a paired chromosome.

Zygote: A diploid cell resulting from the fusion of two haploid gametes.

Gamete: A mature haploid female or male sex cell that is able to unite with the sex cell of the opposite gender to form a zygote.

Fertilization

- Joins two haploid gametes to make a diploid zygote

- Sexual reproduction is production of new individual by joining two haploid gametes

- Sperm and Egg (gametes) unite during fertilization

- Each gamete contributes its set of chromosomes to produce diploid cell called zygote

Somatic Cells versus Gamete Cells

- Somatic Cells are the body cells and are diploid. (2n) (n=haploid number of chromosomes)

- SOMATIC CELLS ARE PRODUCED BY MITOSIS

Germ Cells (or Gametes) are the sex cells and are haploid. (n)

- GERM CELLS AKA GAMETES ARE PRODUCED BY MEIOSIS.

MORE INFO ON SOMATIC CELLS

Somatic cells are any cell of a living organism other than the sex cells.

They make up all of the cells of the body except the sex cells.

i.e. circulatory, nervous, respiratory, digestive and skeletal system.

Organs have many different cell types, all of which are somatic cells.

Cells in General: They contain cell organelles that each perform a distinct function. All cells contain a nucleus that has the exact same DNA.

- Somatic Cells have a nucleus that has two sets of chromosomes, though. That makes them diploid.

A karyotype of the DNA inside human somatic cell shows all 46 chromosomes. If they were haploid, they would be considered 23 chromosomes in the nucleus. A somatic cell has DNA from both the mother and father.

SUMMARY

Somatic Cells are body cells. They are considered diploid and have 46 paired chromosomes (2n; 2 of each type). They divide by mitosis.

Gametes are sex cells. They are considered haploid and only have one set of chromosomes (n; one of each type). They divide by meiosis.

MITOSIS VIDEO SUMMARY

During mitosis, a cell will undergo mitosis to form two new nuclei and then divide to form two new individual cells during Cytokinesis.

Mitosis is the process of dividing the duplicated DNA of a cell into two nuclei.

Mitosis is split into distinct phases.

Prophase: The DNA condenses, organizes and the classic chromosome structure appears.

Prometaphase: The microtubes attach to the chromosomes.

Metaphase: The chromosomes align.

Anaphase: The chromosomes separate.

Telophase: Nuclear membranes re-appear around the two chromosomes.

After mitosis, two new cells form by the process of cytokinesis.

Mitosis is only one part of what is called the cell cycle.

duplicated every 24 hours

Interphase: consists of three stages called G1, S and G2

- G1: first growth stage of interphase (cell grows to full size)

S: synthesis phase where DNA nucleus is replicated

G2: Gap where the cell finishes growing and mitosis can begin.

Many organisms pass their genes to their offspring through sexual reproduction. This occurs when two gametes unite to form an embryo that is genetically unique from the parent organisms. The embryo grows and then passes to their own offspring.

Sex cells (or germ cells) are developed through meiosis.

Germline cells undergo meiosis to produce haploid gametes which only have one copy of each chromosome. This fuses.

One step in the life cycle of a germ cell.

- Duplicated germline cells are called sister chromatids

- Two cell division events.

Meiosis I: results in two unique daughter cells that have half the amount of DNA as the parent germline cells.

Meiosis II: 4 unique haploid cells that only have one copy of each chromosome.

haploid cells are the gametes that would go off to produce offspring.

Meiosis I Prophase I: duplicated sister chromatids joined together at the centromere.

Synapsis/Crossing over

DNA Section

- There is more DNA than just nuclear DNA. There is also DNA in the mitochondria.

- Somatic cells and Gametes both contain DNA

- Why is DNA so important?

DNA is the molecule of life.

DNA forms nitrogenous bases, which can be written as such:

Adenine pairs with Thymine

Guanine pairs with Cytosine

Base pairs form together to make a sugar phosphate backbone.

Then, it is passed from generation to generation as a double helix. It is made of specific bases that pair complimentarily. This is the coding for all walks of life. These four bases make up our genetic code and serve as the building blocks for how humans are made.

Despite this, DNA has different levels of complexity.

Nucleotides are the building blocks of DNA.

A strand of DNA is formed by covalent linkage of nucleotides.

Two strands of DNA can hydrogen-bond to each other to form a double helix.

In living cells, DNA is associated with an array of proteins to form chromosomes.

A genome is the complete complement of an organism's genetic material.

In fact, a strand of DNA is a linear linkage of nucleotides with directionality.

- Nucleotides are linked together by phosphodiester bond connecting the phosphate group and sugar group.

- Sugar and phosphate groups form the backbone of DNA.

- Bases project inward from the backbone. Thus, the linkage gives orientation denoted 5 prime and 3 prime ends.

This came to be when Chargaff found that DNA linkages occurred with Adenine to Thymine and Cytosine to Guanine. Thus, the discovery of two strands of DNA can interact to form a double helix.

The molecular structure of the double helix has several key features:

1. Double Helix

2. Antiparallel

3. Complimentary strands

But, there is a difference.

NUCLEAR DNA: Double stranded and linear, contained within the nuclear membrane, made up of 3.3 million base pairs, two copies of nuclear genome per somatic cell, 20,000-25,000 genes, accounts for 93% of total DNA, inherited equally by parents

MITOCHONDRIAL DNA: double stranded and circular, not enveloped by a membrane, 16,569 bp in humans, each mitochondrion contains dozens of copies, mitochondrial genome contains 37 genes, inherited only from mother

Endosymbiotic Theory supports the presence of circular DNA in mitochondria.

Nuclear genome is much larger than mitochondrial genome.

(i.e. the nucleus contains two of every chromosome, mitochondria contain hundreds of copies of DNA)

Mitochondrial DNA is inherited only from your mother.

Mutation rate in mitochondria is 20x greater than nuclear DNA.

Mitochondrial diseases affect the ability of mitochondria to produce ATP (energy) and affect many tissues and organs.

GENETIC DETAILS OF CONTROVERSIAL THREE-PARENT BABY

- Quesitons about long-term health

- manipulation of embryo during procedure

- transfer of some diseased DNA

- long term repercussions

- Parents refusing to receive enough treatment and later tests