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What joins together to form a fertilized ovum?
At this time, the _______ number (n) of chromosomes found in each gamete will join with the other _______ gamete (n) to form the DIPLOID zygote (2n).
How many pairs of chromosomes are found in a human diploid zygote?
23 pairs of chromosomes
How many pairs of chromosomes are found in a human diploid zygote?
23 pairs...46 chromosomes
At which level does differentiation start to take place?
At the blastocyst level
What is "cleavage"?
Mitotic division that leads to a multicellular structure.
Why do all the cells in the body have the same genetic information?
Because mitosis is the central process that allows an increase in the number of cells while keeping the DNA identical from one division to the next.
What is differentiation?
When identical cells start to be assigned specific functions in the body and specialized into different organs and parts of the body.
What are the three distinct layers of the cells that form during differentiation?
- ECTODERM: outer layer, forms the skin and the nervous system
- MESODERM: the middle layer, forms connective tissue
- ENDODERM: inner layer, forms most of the viscera
What is organogenesis?
The formation of the organs from the germ layers and involves a coordinated interplay between the developing tissues.
What is happening on a cellular level during differentiation?
Different segments of the chromosomes will code for specific proteins (genes).
What tightly coordinates and "regulates" the development of organs during differentiation?
HOMEOBOX GENES - "master genes"
What happens at the cellular level during the embryological/fetal life?
Different portions of the DNA molecules are open, different genes are being expressed than after birth.
What is an example of the changes of DNA during fetal life?
Before birth, a gene is transcribed that codes for fetal hemoglobin in the RBCs - after birth, this area of the chromosomes closes and another area opens.
What happens to the production of AFP (alpha-fetoprotein) during development?
Fetal cells produce AFP and after birth, these genes close and AFP is no longer produced.
What are the two categories that the 46 chromosomes can be divided into?
- 22 pairs of AUTOSOMES
- 2 SEX CHROMOSOMES
What are HOMOLOGOUS PAIRS?
- A pair of chromosomes, one from each parent, that have the same size and shape and code for the same traits.
What are ALLELES?
Different versions/variations of a gene.
What are Homozygous Alleles?
Two alleles that are the same...like traits.
What are Heterozygous Alleles?
Different alleges...different traits.
What is Genotype?
Alleles present that determines which proteins that are made that lead to the trait observed (Phenotype).
How is phenotype determined?
It depends on whether the alleles are DOMINANT or RECESSIVE.
What determines for a dominant disease to be expressed?
- Only one parent needs to donate the information to the offspring.
- The dominant gene masks the recessive gene from the other parent.
- An autosomal disease
- Due to mutation of the gene on chromosome 15, that controls the production of FIBRILLIN (a connective tissue protein)
What are the signs and symptoms of Marfan Syndrome?
- A tall, slender build
- Elongated head
- Loose joints and weak ligaments
- Eye lens problems and cataracts are common.
- Pectus Excavatum (sunken chest)
- Arachnodactyly (long slender fingers and toes)
- Autosomal Dominant Disease
- An abnormal gene on chromosome 19
- The gene mutation encodes for cholesterol receptors that blood cholesterol (LDL) can not enter the cells as usual.
What happens in a person with Familial Hypercholesterolemia?
- An increased amount of circulating cholesterol in the blood.
- This deposits in various tissues which can lead to atherosclerosis and coronary heart disease especially earlier in life (men: 40s-50s, women: 50s-60s).
What are the ranges for cholesterol levels - normal vs. Familial Hypercholesterolemia?
- Normal LDL: less than 100 mg/dL
- Familial Hypercholesterolemia LDL: greater than 220 mg/dL
Huntington's Disease (HD):
- An autosomal dominant disease.
- Results from genetically programmed degeneration of neurons in the basal ganglia and cortical regions of the brain.
- Symptoms appear in mid-40s.
- The gene is on chromosome 4.
What are the clinical manifestations of Huntingtons Disease?
- Loss of intellectual faculties, emotional disturbance and dyskinesia (difficulty performing voluntary movements)
- Parts of the brain dealing with movement are compromised, with a loss of neurons in the substantia nigra (similar to Parkinson's Disease)
What are the possible treatments for Huntington's Disease?
- There is no cure for HD
- Stem cell therapy is being explored
- Experimental drugs have shown some promise in animal models.
What are some examples of Autosomal Dominant Diseases?
- Marfan Syndrome
- Familial Hypercholesterolemia
- Huntington's Disease
What are some examples of Autosomal Recessive Diseases?
- Cystic Fibrosis
- Tay-Sachs Disease
- Phenylketonuria (PKU)
- Trisomy 21 (Down's Syndrome)
- Trisomy 18 (Edward's Syndrome)
What occurs to make a autosomal recessive disease to occur?
- In order for a person to express a Recessive Disease, BOTH parents must donate a gene for that disease.
- Only if the offspring receive a "double-dose" of the mutated gene.
What are Carriers of recessive diseases?
- Individuals who have the genetic information for a specific disease (genotype) but who phenotypically will not have it.
- The genetic info is "carried" or passed on to the offspring.
- An Autosomal RECESSIVE disease most common among Caucasians, especially those of Scandinavian decent.
- The gene, found on chromosome 7, makes the membrane channels on glandular epithelial cell surfaces nonfunctional.
- Prevents the passage of chloride into the secretory cells affecting water movement and mucus secretions build ups.
- The ducts of the exocrine glands become blocked.
What are the clinical manifestations of Cystic Fibrosis?
- Bronchi of the lungs are affected resulting in chronic bronchitis and recurrent pneumonia.
- Blockage of the pancreatic ducts - malabsorption may occur as a lack of digestive pancreatic enzymes...pancreatitis.
- Infertility - thick mucus obstructing the vas deferens tubes in males and cervix in females
What are some of the treatments for Cystic Fibrosis?
- Medication to thin the mucus (mucolytic medication).
- Chest percussions
- Pancreatic enzyme replacement
- nutritionist therapy
How does ones life affected by Cystic Fibrosis result?
- Cystic Fibrosis is incurable.
- Many die between ages 20-40 due to pulmonary and digestive problems.
- A rare condition that arises when there is a mutation in the enzymes found inside of the lysosomes, and organelle of the cell.
- Found on chromosome 15.
- Lipid metabolism is affected leading to the accumulation of fatty substances within the neurons and eyes (retina).
When does Tay-Sachs Disease become apparent?
- Between the ages of 3 to 6
- Their development slows and muscles used for movement weaken...they lose their motor skills.
- They develop an exaggerated startle reaction to loud noises.
- Adult onset can happen but is very rare.
What are the clinical manifestations of Tay-Sachs disease?
- Exaggerated startle reaction to loud noises.
- Seizures, vision and hearing loss, intellectual disability, paralysis.
- A Cherry-red spot in the eye is characteristic of this disorder.
What is the mortality of Tay-Sachs disease?
- Very rare in general population.
- Live only into early childhood.
- More common in people of Ashkenazi Jewish heritage, French-Canadian communities of Quebec, Old Order Amish of Pennsylvania, Cajun population of Louisiana.
- Autosomal Recessive Disease.
- A defective gene results in the production of defective PAH (phenylalanine hydroxylase), allowing for a build up of phenylalanine from digested food.
Clinical manifestations of PKU:
- Phenylalanine will collect and mental retardation will develop.
- Changes in diet can be followed that will avoid excess phenylalanine.
- Routine blood tests shortly after birth, helps determine this disease in an infant.