LECTURE 5: DNA, CHROMOSOMES, AND GENES
1.DNA is an information molecule with a double helix. This means that two complementary strands are wound together. These strands are held together with hydrogen bonds.
2.DNA is made of nucleotides¸ each of which is made of a phosphate, sugar, and a base. The sugar and the phosphate make up the sugar phosphate backbone of DNA. These bases make up genetic instructions.
3.The bases of DNA are complementary¸ meaning that one base always pairs with the same strand. The C ( Cytosine), G ( Guanine), A ( Adenine) and T ( Thymine)—in RNA, this base is U ( Uracil).
4.All living things contain these four bases! The amount / number of bases in organisms make the DNA different. More pairs do not mean a ‘ better’ or more sophisticated organism.
5.The order of the bases also many DNA different. The bases code for amino acids, which make up specific proteins that make a unique individual.
6.In the Prokaryotic Cell, the DNA is floating in the cytoplasm inside of the nucleoid. In the Eukaryotic Cell, the DNA is housed inside of a solid nucleus in the cytoplasm.
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7.DNA is neatly packaged in the nucleus. The base pair makes itself into the helix, then more tightly around the histones (like pearls on a string). The histones get super close and coil up into nucleosomes, and then chromosomes.
8.Humans have 23 pairs of chromosomes, 46 total. These pairs are called homologous. One is donated by the father, sperm, the other is donated by the mother, via egg.
9.When all of the chromosomal pairs are laid out in a row, it is called a karyotype. Each chromosome is made out of genes.
10. Genes are the basic unit of heredity (or the passing of traits from parent to offspring). Genes are sets of instructions to produce these traits (like eye color). Genes are the portion of DNA that codes for a trait. Proteins are the biological correlate of traits (like blue eyes are a trait. That eye color pigment is made of a certain protein). If you want to learn more check out Who said disease and famine kept population numbers down?
11. In order for the cells to produce these traits, they need to read their genes, follow the
instructions, and make proteins; this making of proteins is called gene expression. This has two phases, transcription and translation.
12. In the first phase (transcription), DNA for a certain gene is unwound and a complementary mRNA strand is produced. This takes place in the nucleus. Bases of the ribo-sugar backbone are bonded via hydrogen bonds. Bonds open so that the cell can make mRNA (messenger RNA) to form a complementary strand (ACGU). DNA is unwound and mRNA strand is formed because DNA can never leave the nucleus.
13. In the second phase (translation), the RNA strand leaves the nucleus, meets up with a ribosome and instructs the cell how to build the protein for that gene. This takes place in the cytoplasm. mRNA leaves the nucleus to tell the ribosome how to build the protein for that gene.
14. Chromosomes carry genes. The locus is the specific place on a chromosome where a specific gene is found. We also discuss several other topics like What is the definition of organic organizations?
15. All members of a species have the same genes on the same chromosomes at the same loci. The reason why all humans don’t have the same diseases is because we all have different
alleles. Everyone has two alleles for every gene, one from their mom and one from their dad. They may be the same allele or they may be different alleles of the gene. Some alleles are more susceptible to diseases than others, so we don’t all have the same diseases (or chances for opportunities) to get diseases. Don't forget about the age old question of What is the meaning of transponders in satellites?
LECTURE 6: THE CELL CYCLE
1.The cell cycle is a repeating series of event that include:
a. Growth of the cell
b. DNA synthesis
2. Interphase is cell growth and preparation for division
3.The mitotic phase is the act of cell division
4.Interphase can be subdivided into the following three phases:
a.Growth phase 1 ( G1; Gap Phase 1): i. Cell grows rapidly, makes proteins
needed for DNA replication, copies
some of its organelles
ii. A cell typically spends most of its life in this phase
b. Synthesis Phase (S):
i. Cell’s DNA is copied in the process of DNA replication
c.Growth Phase 2 (G2; Gap Phase 2): i. The cell makes final preparations to divide
5.After cells grow to their maximum size, they divide into two new cells. One parent cell ends up as being two identical daughter cells. Each daughter cell is diploid, which means it We also discuss several other topics like What does meteorology mean?
contains 23 pairs of chromosomes. We also discuss several other topics like What is the eustachian tube?
6.If the cell needs to divide, first it needs to make more DNA. This is DNA replication. The DNA opens, the enzymes copy both sides, and complementary bases are added. DNA replication is semiconservative, which means that each new strand is half old and half new.
7.After replication is complete, both double helixes (sister chromatids) stay connected for a while. They are still considered one
chromosome (a replicated chromosome). The part of the chromosome that links sister chromatids is called the centriole. Each copy contains exactly the same information.
8.The four stages of mitosis are prophase, metaphase, anaphase, and telophase. a. Prophase: from the parent cell, chromatin condenses into chromosomes and the nuclear membrane breaks down. Centrioles move to opposite poles of the cell and spindles start to form between them.
b. Metaphase: the sister chromatids line up at the equator of the cell. Spindles attach to centromere.
c. Anaphase: the sister chromatids are pulled apart to opposite ends of the cell by the shortening of the spindle fibers.
d. Telophase: chromosomes uncoil and form chromatin. The spindle also breaks down, and new nuclear membranes form. This process creates two daughter cells.
9. Cytokinesis is the final stage of cell division where the cytoplasm splits in two and the cell divides.
10. Cell division:
a.Sometimes a cell never divides:
i. the heart muscle
ii. the liver
iii. the kidneys
iv. mature brain cells
b.the cell might need to divide for:
ii. repairing damage
iii. replace dead cells
11. There are checkpoints in cell division. If a cell doesn’t pass a checkpoint, it initiates apoptosis, which is programmed cell death. a. The checkpoints are:
i. Metaphase anaphase (are all of the chromosomes aligned at the equator?) ii. G1 S (is the DNA intact?)
iii. G2 M (has the DNA been completely replicated?)
12. The two types of cell division are mitosis (how body (somatic) cells divide) and meiosis (how sex cells (gametes, like sperm or eggs) divide
13. Sexual reproduction requires sex cells (gametes). The male gamete is sperm (spermatozoa), and the female gamete is the egg (ovum). The gametes are haploid cells, which means that they only carry half of the number of chromosomes of other cells. The mother give 22 pairs of chromosomes and an XX pair, and the father gives 22 pairs of chromosomes and an XY pair, equaling 46 pairs of chromosomes in the zygote.
14. There are two types of twins, identical and fraternal.
15. Monozygotic (MZ) twins, single ovulated egg fertilized by one sperm. The embryo splits into two—monozygotic twins (100% genetic identity).
16. Fraternal (dizygotic (DZ)) twins, two ovulated eggs fertilized by different sperm— decrease in genetic dissimilarity relative to unrelated individuals
a. 25% decrease in genotypic dissimilarity b. 50% decrease in allelic dissimilarity.
17. A parent can only give what they have, so a mother is only able to give an X
chromosome, while a father is able to give an X or a Y.
18. From fertilization, zygotes are either XY (genetically male) or XX (genetically female). For the first month, XX and XY fetuses appear identical, which means that they have undifferentiated genitalia. If the fetus has Y chromosome (male), the gene on the Y chromosome (the SRY gene) causes testes to develop, which secrete testosterone to masculinize genitalia. Hormones secreted by testes (like testosterone) masculinizes the body and brain—this occurs in utero as well as throughout life. If the fetus has no Y
chromosome (female) there is no SRY gene, and the genitalia is feminized. In puberty, ovaries secrete hormones (like estrogen and progesterone) that feminize the body and brain.
19. Meiosis is cell division of gamete (or sex) cells—in males, these are sperm; in females, these are eggs. Gametes come from germ cells in testes or ovaries. Two cell divisions occur during meiosis, and a total of four haploid daughter cells are produced (Meiosis I and
Meiosis II, which has similar steps as mitosis, but in two back-to-back cycles).
20. Chromosomal crossover (or crossing over) is the exchange of genetic material between homologous chromosomes that results in recombinant chromosomes. Chromosomes replicate prior to meiosis, then like
chromosomes pair up and swap sections of DNA, creating a mix of new genetic material in the offspring’s cell. The nucleus divides twice into daughter nuclei and the daughter nuclei have single chromosomes and a new mix of genetic material. In Meiosis I, homologous chromosomes line up and exchange alleles, which add genetic diversity to daughter cells.
21. Without crossing over, each couple has the potential to produce around 750 genetically unique offspring. Each human couple actually has the potential to produce more than 64 trillion genetically unique children.
LECTURE 7: GENETICS
1. Genetics are the study of genes, heredity, and genetic variation in living organisms.
2. Homozygous is when an individual inherits the same alleles for a particular gene from both parents.
3. Heterozygous is when an individual inherits two different alleles for a particular gene.
4.A dominant allele is one that produces the phenotype (represented by upper case letters).
5.A recessive allele is one that only expresses its phenotype if there is no dominant allele (represented by lower case letters).
6.A genotype is the genes that an organism has.
7.A phenotype is the trait that the organism expresses.
8. Gametes are the connection between generations (egg and sperm). Gametes are haploid, so they have 1 allele for every gene.
9. Gregor Mendel is the “Father of Genetics.” He was a monk that raised pea plants. He made careful observations of the traits of pea plants that grew during each season. Mendelian Inheritance = simple dominant/recessive.
10. The Law of Segregation says that each organism has two hereditary units for each trait (two of each gene) and during gamete formation, these units separate from each other and pass into different gametes (meiosis).
11. The Law of Independent Assortment says that in the formation of gametes, the distribution of hereditary units for one trait is independent of the distribution of hereditary units for the other trait.
12. The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment.
13. Holstein cattle have a spotted coat due to a recessive allele while a solid colored coat is dominant. The genotypes are spotted x spotted, the parent genotypes are hh x hh. Because the only thing that the parents can give is the spotted trait, the only possibility for the offspring is to be spotted.
14. In mice, black fur (B) is dominant to brown fur (b). a cross between a brown and a black mouse produces all black mice. The parent genotypes are BB x bb, so all of the offspring are going to be dark-brown/black-furred.
15. Incomplete Dominance says that a ‘dominant’ allele doesn’t fully cover up a ‘recessive’ allele.
a.A = straight hair
b.a = curly hair
i. Aa = wavy hair
1.R = red
2.W = white
3.RR = red flowers
4.WW = white flowers
5.RW = pink flowers
16. Gene is on a sex chromosome, either on the X or Y chromosome. Males have XY, females do not have Y. females have XX, males only have X. more X-linked than Y-linked traits
in humans (because the X chromosome is bigger).
1.Condition is recessive (like
a.Father is unaffected
b.Mother is carrier
c.All daughters are unaffected
d. ½ of daughters are carriers
e. ½ of sons are affected
2.Dominant condition (rare)
a.On the X chromosome
b.Father has condition
c.Father gives Y to every son
i. With unaffected mother, all
sons are unaffected
d.Father gives X to every
i. all daughters are affected,
regardless of mother
3.Dominant condition (rare)
a.Mother is heterozygous—
b.Since mother gives an X to
every child, there is a 50%
probability that any child from
this mother will be affected
17. Females and X-linked traits
a.Every cell in our body contains all our DNA b.Every cell in a female’s body contains XX chromosomes
c.Each X chromosome has the exact same genes on it, only different (maybe!) alleles of that gene
i. In cells that express an X-linked gene, which X chromosomes is it expressed on?
a. NOT BOTH
b. One or the other!
i. The inactive X chromosome
coils up so tightly that it
can’t be read (Barr body)
18. Example: Calico Cats
a.Fur color is on the X chromosome
b.One X has allele for brown fur
c.One X has allele for black fur
d.Some cells can’t express pigment
e.Male calico cats are so rare, 1/ 3000 chance!
a.Neither allele covers up the other
b.Both are dominant, both are expressed
20. Multiple alleles:
a.More than two options
b.Each person will only have to alleles for the gene
21. There are three possible alleles
b.You only get two
c.Six possible genotypes
d.Four possible phenotypes
22. Environmental effects:
a.Even though DNA says one thing, the phenotype can be altered by
i. Siamese cats have a heat-sensitive pigment protein
ii. This protein is expressed more in areas of their bodies that are cooler
a.In warmer temperatures, the
fur becomes lighter
b.In cooler temperatures, the fur
23. Lethal alleles:
a.In crossing a yellow (AY) (mutated) mouse with an agouti (A) (brown, natural) mouse, the offspring turns out as brown. In
crossing two yellow mice (AYAY), the
offspring is not even born, but dies as an embryo.
24. Continuous variation:
a.Several genes work together to produce one phenotype
b.Many different possible phenotypes, such as human skin color
25. One gene, multiple effects:
a.A single gene can cause many effects b.Example: gene for albinism
i. Lack pigment in hair and skin
ii. Also have higher rate of crossed eyes (because gene also controls how eves connect to brain)
LECTURE 8, “EPIGENETICS”
1.Chromosomes are composed of chromatin, which is DNA wound around proteins called “histones,” which are a protein associated with DNA.
2. Methylation of DNA and histones causes nucleosomes to pack tightly together.
Transcription factors cannot bind the DNA, and genes are not expressed.
a.Transcription factors = proteins that
facilitate gene transcription. Nucleosome = small portion of DNA wrapped around a histone.
3.Histone acetylation results in loose packing of nucleosomes.
a.Transcription factors can bind the DNA and genes are expressed.
4. Methyl groups and acetyl groups are responsible for regulating which genes are expressed. This means that these chemicals control gene activity and their presence or absence within a cell or at a specific gene dictates what that cell does—this influences “who” we are.
5.Our experiences shape our genes—not which genes we have, but where, when. And how they are being expressed
6. Epigenetics is the study of phenotypic trait variations caused by external/environmental factors that switch genes on and off and affect how cells read genes. These are NOT caused by changed in the DNA sequence.
7.How are changes in gene expression due to external factors involved in:
e.Changes in our offspring
LECTURE 9, “CHROMOSOMAL ABNORMALITIES”
1.Chromosomal abnormality—a missing, extra, or irregular portion of chromosomal DNA a.Problems in number of chromosomes – too many or too few of a chromosome
b.Missing pieces of chromosomes – some pieces of a chromosome may be lost or rearranged
c.Translocations on chromosomes – a piece of a chromosome breaks off and reattaches d.Single gene mutations
a.The number and appearance of
chromosomes in the nucleus of a
eukaryotic cell. We can compare an
individual’s karyotype to the normal karyotype to determine the existence of a chromosomal abnormality.
b.Pair of homologous chromosomes:
i. One from mom and one from dad
ii. Have the same genes arranged in the same order
iii. Slightly different DNA sequences
a.Chromosomal abnormalities result in various symptoms based upon the
chromosome affected and how
b.Problems in number of chromosomes: i. Nondisjunction
ii. Problems in structure of chromosomes 1.Deletion
iii. Single gene mutations
4.Problems in number: nondisjunction
a.Each species has a specific number of chromosomes
b.If homologous chromosomes don’t
separate properly during cell division (this is called nondisjunction), you get cells with incorrect numbers of chromosomes
c. Aneuploidy: an abnormal number of chromosomes
i. Monosomy = when an individual is missing a chromosome from a pair
ii. When an individual has more than two chromosomes of a pair = trisomy,
5.Trisomy21: Down Syndrome
a.Occurs when individual has three copies of chromosome 21
i. spots on the eye, flattened facial
profile, poor muscle tone, short stature, etc
i. speech delay, intellectual disability, impulsivity, etc
e.Older women have increased risk because the eggs are older and have a greater risk of improper chromosome division
6.Trisomy13: Patau Syndrome
a.Most lethal trisomy with median survival is 3 days – many are miscarried
i. Severe mental deficiency, facial
clefting, neurological and heart defects c. 1/9500 births
d.Increased risk with mother’s age
7.XXY: Klinefelter Syndrome:
a.Genotype is male
b.Phenotype can be male, female, or intersex – usually make
c. 1/500 – 1/1000 male births
d.Extra X could come from mother or father e.Symptoms:
i. Sterility, less testosterone production leading to slightly feminized
appearance in adolescence (less
muscle tone, less body hair,
ii. May have cognitive and physical delays
8.XO: Turner Syndrome:
a.Genotype and phenotype female
b.Only 45 chromosomes
c. 1/2500 girl births
d.Missing chromosome from mother or father e.Symptoms:
i. Short stature, webbed neck, broad chest, etc
f. some have difficulty with imagining objects in relation to each other, nonverbal
memory and attention, sense of direction, manual dexterity, nonverbal learning and social skills
9.XYY: XYY Syndrome:
a.1/1000 boy births
b.Usually no huge impact, most don’t even know
c.Boys with XYY karyotype have an increased growth velocity from early childhood, with an average final height approximately 7 cm (3”) above expected final height
10. Problems in structure
a.Typically occur due to errors in crossover i. Deletion
a.Part of a chromosome is
a.Production of one or more
copies of any piece of DNA
a.Segment of a chromosome is
reversed end to end
a.Rearrangement of parts
a.Cri du chat, “cat’s cry” syndrome
b.Deletion on chromosome 5
c.Extent of deletion varies
d.Symptoms = intellectual disability and delayed development, small head size (microcephaly), low birth weight, and weak muscle tone
e.1/20000 – 1/50000 births
f. From mother or father
b.Genetic information at the q21.1 position of chromosome 1 is duplicated at least once c.May represent a number of symptoms including:
ii. Large head
iii. Learning disability
iv. Heart defects
v. Seizures, etc
d.Prevalence is unknown, but 1/700 people tested for 1q21.1 have it
13. Inversion: inv(9)p12q13
a.Inversion of chromosome 9 – inv(9)p12q13 b.Most common inversion
i. Occurs in 2% of population
d.Some controversial reports suggest it contributes to male infertility
b.Translocation of chromosome 9&22 c.Contributes to chronic myelogenous leukemia (CML)
15. Single Gene Mutations
a. Alteration in the DNA sequences forming a single gene
b.May be inherited or acquired through environmental exposure
c.A mutated gene will not be able to produce the correct amino sequence, which may lead to problems
i. E.g., Huntington’s Disease
a.Brain disorder affecting ability
to think, talk, and move
b.Mutation in a gene on
chromosome 4, which codes for
the huntingtin protein
c.Normally, this gene’s DNA
sequence contains “CAG”
repeated again and again
(usually 10-20 times)
d.People with Huntington’s
Disease have an abnormally
high number of these CAG
triplets (around 40+)
e.The brain cells of Huntington’s
Disease patients accumulate
clumps of protein that become
toxic, resulting in cell death
f. Some patients lose more than
25% of their brain cells before
16. You need the correct number of chromosomes
a.You need the chromosomes to have all of the genes
b. You need the genes to have the correct order of bases