Chapter 1- Overview of genetics
• Genes and alleles
• DNAand RNA
• Genetic Testing
Genes and Alleles
Gene – segment of DNA(a gene codes for production of a protein)
Allele – variant of a gene
Protein gives the animal a characteristic- example allele can code for a flower to be purple :: a
white allele codes for no pigment.
Example: Sickle-cell anemia
• Caused by mutated gene - codes for component of hemoglobin (carries oxygen through
• An allele of the gene codes for a defective hemoglobin (doesn't make a functional
• Result is sickle-cell anemia.
3 billion base pairs in a human genome- 1 change can cause sickle cell-- changing from a T to an
A-- makes an abnormal protein
• DNA = Deoxyribonucleic acid. (Sugar Oxyribose)
– 4 DNAbuilding blocks:A, T, G, C
Aattaches to T, G attaches to C
• RNA = Ribonucleic acid. Intermediary between genes and proteins. (Sugar Ribose)
– 4 RNAbuilding blocks:A, U, G, C
Ain DNA= a U in RNA- theres no T in RNA
• Long strand of DNAand proteins. Each chromosome contains many genes.
• Humans: 46 chromosomes in all cells except sperm and eggs.
– 23 from mom
– 23 from dad
• All genes in cells of a particular type of organism.
• Human genome is approximately 20,000 genes
• Corn has 30,000 genes and the worm C. elegans has 10,000 Genotype and Phenotype
Genotype – alleles an organism contains
Phenotype – how those alleles are expressed (what the organism looks like- appearance).
Ex: Flower color
PP = purple (homozygous)
Pp = purple (heterozygous)
pP = purple (heterozygous)
pp = white (homozygous)
Ratio 1:2:1 (genotype) 3:1 (phenotype)
• Chart that displays chromosome pairs in size order.
- organize chromosomes into pairs in chart then arrange them by size
• How can we use a karyotype?
- Some genetic conditions can be viewed in a karyotype- ex. 1 extra, 1 less chromosome
3 chromosomes in the 21st pair (Trisomy 21) - Down syndrome
- Large Genetic mutations
radiation can cause a mutation
• Gregor Mendel
• Studied traits determined by a single gene.
• One gene causes a specific phenotype (disease) - one gene determines 1 trait
• Examples: Sickle-cell anemia, cystic fibrosis, hemophilia
Are all genetic traits Mendelian? No: ex, eyes, height, skin color
• How many genes determine human height?
• How many genes determine eye, hair, and skin color?
• How many genes determine the development of heart disease?
^^ these are polygentic traits- many genes involved
ONE GENE DOES NOT LEAD TO ONE DISEASE
• Atrait caused by one or more genes and the environment.
• Examples: height (genetics and nutrition), hair color, hypertension, breast cancer,
• Genetic factors: BRCA1 and BRCA2 – genes that contribute to development of breast
• Non-genetic factors: early menarche, late menopause, first child after age 30, hormone
replacement therapy--- (all 4 increases estrogen and extra estrogen increase chance for
cancer), alcohol use radiation exposure, chemical exposure, obesity. Risk is reduced by
low-fat and high fiber diet, regular exercise. ***** most important- affects people more
• Syndrome factors: Some breast cancers are related to other genetic syndromes (ex:
Werner’s syndrome) Genetic Testing
• Analysis of human DNA, RNA, chromosomes, proteins, or metabolites, to detect
genotypes, mutations, or chromosomal changes
• 2008: Genetic Information NondiscriminationAct (GINA) - insurance companies or
employers cannot deny healthcare based on what is found in genetic testing
• Direct-to-consumer genetic tests - no doctors involved - ex. 23andMe.com
Cell Components and the Cell Cycle
Macromolecules (Macro-big) (organic-carbon)
• Enzymes: speed up reactions
• Provide structural support
• *Control gene expression - cells have specific proteins that turn on a gene to determine
where it will lie in the body- (skin cells become skin cells)
Prions – rogue proteins - protein can become infected and change its shape - change in shape,
changes the function (proteins can be infectious)
• Cause “Mad Cow Disease”
• Provide energy for cell metabolism
• Provide structural support
• Provide cell identity
Starch turns into glucose --- cannot digest cellulose
• Provide energy (dietary fats)
• Are main component of cell membranes
• Many are hormones (chemical messengers)
Ex of lipids- estrogen, testosterone
• *Genetic material
• Energy source- ATP
• Endoplasmic reticulum
• Golgi apparatus
• Lysosomes • Peroxisomes
• Cell Membrane
• Modifications to these structures can result in disease
genetic material- DNAnever leaves nucleus
connected to nucleus- two types:
Rough: site of protein synthesis for export out of cell- ribosomes attached
Smooth: detoxify toxins--- no role ins production of proteins
Liver has a large amount of smooth ER- detox
Proteins are modified and labeled for transport outside cell (export)
Contain digestive enzymes that breakdown cellular material (gets rid of worn out/ no
functional organelles--- get recycled----- increase efficiency of cells)
produce bile for fat digestion
Maternally inherited, have their own genes
ProduceATP- necessary for cells to do work
maintains cell shape and structure
Helps move substances around cells
What role does the cytoskeleton play in cancer cells?
Cancer- uncontrolled cell division
Dividing cells use cytoskeleton to move chromosomes apart. if cytoskeleton is disrupted, cell
Made of phospholipids and proteins
control movements of substances in and out of cell
What are ions? something with a pos/neg charge----
How do ions move through the cell--- travel through
what happens if someone has faulty ion channels?
Cellular disorders that result in disease - HPP and abnormal Na+ channels
- Long QT syndrome and K+ channels
- Cystic fibrosis and Cl- Channels
Why are disease that result from faulty ion channels considers genetic disease?
Ion channels are proteins and proteins are coded for by DNA
• Mitosis or Meiosis
• Mitosis – cell division for growth, repair (cloning division – daughter cells are genetically
identical to parent cell)
• Meiosis – cell division for reproduction (produces eggs and sperm and generates genetic
before a cell divides its a single strained, then it doubles to replicate
The 2 strands of the replicated chromosome are “chromatids”.
They are genetically identical to each other.
• Interphase – chromosomes are replicated ----
most of the cell cycle--- everything but
mitosis--- S phase of interphase is when
DNAis being relicated
• Mitosis – division of nucleus and cytoplasm. Control of Cell Cycle
• Most cells divide a limited number of times
• Telomeres (tips of chromosomes) are degraded with each mitosis
• Programmed cell death
• “Death receptor” receives signal for cell to die – enzymes in cell begin degrading cell
1. Totipotent cells – cells that can differentiate into any cell type
Meiosis and Development
Meiosis – why does this happen?
2. Cell division for reproduction
3. Diploid cell (2n) 4 haploid cells (1n)
o Mitosis: 1 (2n) 2(2n) = cloning
4. Each daughter cell is different from others
5. Generates genetic diversity
equation used to determine the # of chromosome combination that are possible
2^n = # of combos
n= # of chromosomes pairs
how many different combinations are possible in a diploid cell of 8 chromosomes?
2^4 Meiosis I
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I
• Meiosis I: reduces ploidy level and separates homologous chromosomes
• Chromosomes w/ same size, shape, and linear arrangement of genes (can have different
Meiosis I: reduction division
Meiosis II: equational division
Prophase I – What happens?
• Chromosomes condense
• Homologous chromosomes synapse (attach to each other)
• Crossing over can occur
• Crossing over produces
• genetic diversity
When a cell with 2 chromosome pairs goes through meiosis, how many different chromosome
arrangements are possible?
• 4 possible chromosome arrangements
When a cell with 3 chromosome pairs goes through meiosis, how many different chromosome
arrangements are possible?
• 8 possible chromosome arrangements n
# possible arrangements = 2
n=# of homologous pairs
• Metaphase I
• Non-homologous chromosomes line up independently of each other
After meiosis, gametes mature into sperm and eggs
• Where are sperm formed in the human male?
• Where are eggs formed in the human female?
• Spermatogonium (2n): precursor to sperm cells
• Spermatogonium (Mitosis) primary spermatocyte (2n)
• primary spermatocyte (Meiosis I) secondary spermatocyte (1n)
• secondary spermatocyte (Meiosis II) spermatid
• Each spermatid then develops flagella and becomes individual spermatozoa
• Sperm are small and do not house many organelles (nucleus and mitochondria)
Contains nucleus and acrosome (digestive enzymes to enter egg) Oogenesis
• Oogonium (2n): precursor to egg cells
• Oogonium (Mitosis) primary oocyte (2n)
• primary oocyte (Meiosis I) secondary oocyte and polar body (1n)
• secondary oocyte (Meiosis II) ovum and polar body
• Ovum gets most of the cytoplasm
• Eggs arrest in Prophase I until puberty – then continue to metaphase II and arrest again