HEREDITY and GENETICS Table of Contents · • The environment also influences quantitative...

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HEREDITY and GENETICS

Table of Contents DNA (Deoxyribonucleic Acid) ................................................................. 2

DNA Research & Technology ................................................................. 3 Genetic Changes ................................................................. 4

Genome Organization & Expression in Eukaryotes ...….............................................. 7 Mendelian Genetics ................................................................. 9

Protein Synthesis ................................................................. 10 Genetic Code ................................................................. 10

Quiz ................................................................. 12


DNA (Deoxyribonucleic Acid)

The DNA holds the genetic information of living organisms, which ultimately determines an organism’s traits. The DNA has the complete instructions for manufacturing all the proteins for an organism.

DNA Structure

• The structure is in the shape of a double helix that contains chains of nucleotides. • In each chain of nucleotides, the sugar of one nucleotide is joined to the phosphate group

of the next nucleotide by a covalent bond. • The two chains of nucleotides in a DNA molecule

are held together by hydrogen bonds between the bases.

• There are four nitrogen bases (carbon ring structures that contain one or more atoms of nitrogen): Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). Cytosine forms hydrogen bonds with guanine, and thymine bonds with adenine.

• This pairing produces a long, two-stranded molecule that is often compared to a zipper. The sides of the “zipper” are formed by the sugar and phosphate units, while the teeth of the zipper are the pairs of bases.

DNA Replication

• DNA replication is the process of making copies of DNA.

• DNA is copied during the interphase prior to mitosis and meiosis.

• When a DNA molecule replicates, two molecules are formed. Each molecule has one original strand and one new strand (semiconservative replication).


Activities

1. Separation of strands. When a cell begins to copy its DNA, the two nucleotide strands of a DNA molecule first separate at their base pairs when the hydrogen bonds connecting the base pairs are broken. As the DNA molecule unzips, the nucleotides are exposed.

2. Base pairing. Free nucleotides base pair with exposed nucleotides. If one nucleotide on a strand has thymine as base, the free nucleotide that pairs with it would be adenine. If the strand contains cytosine, a free guanine nucleotide will pair with it. Thus, each strand builds its complement by base pairing with free nucleotides.

3. Bonding of bases. The sugar and phosphate parts of adjacent nucleotides bond together to form the backbone of the new strand. Each original strand is now bonded to a new strand.

DNA Research and Technology Medical and Pharmaceutical Industry Recombinant DNA technology

• Diagnostic tests for detecting mutations that cause genetic disease were developed. • Safer and more effective vaccines were designed. • Large-scale production of many new, and some previously scarce, pharmaceutical

products were manufactured. • Genetic disorders caused by defective genes were cured and prevented.

Forensic, Environmental and Agricultural Application

• DNA “fingerprints” obtained from satellite DNA analysis of blood, hair, or other materials found at the scenes of violent crimes as evidence in court trials.

• Genetic engineering for modification in the metabolism of microorganisms, specifically decomposers.

In agriculture, transgenic plants and animals (organisms containing genes from other species) are being designed to improve productivity and food quality. This is done by the insertion of recombinant DNA molecules into the DNA of plants and animals.


Genetic Changes DNA Mutation

• DNA mutation involves any change in the DNA sequence. • Mutation can affect the reproductive cells of an organism by changing the sequence of

nucleotides within a gene in a sperm or an egg cell and further result in the formation of structural and functional problems in cells of the offspring.

• If the DNA of a non-reproductive cell is mutated, the mutated gene will not be passed on the offspring, but may cause problems to the individual parent.

Types of DNA mutation: 1. Point mutation is the change in a single base pair in DNA due to the insertion of

incorrect amino acids into a growing protein chain during translation. 2. Frameshift mutation occurs when a single base is added or deleted from the

DNA due to a shift in the reading of codons by one base. This results to a change in the entire protein structure specifically in the location after the deletion or addition of codons.

Chromosomal Mutation • Parts of chromosomes are broken off and lost during mitosis or meiosis. • Chromosomal mutation is common in plants.

Parts of a chromosome

(1) Sister chromatid. One of the two identical parts of the chromosome after S phase. (2) Centromere. The point where the two chromatids touch, and where the microtubules attach. (3) Short arm (4) Long arm.


Types of Chromosomal Mutation

1. Deletions occur when a chromosomal fragment lacking a centromere is lost during cell division. This causes the loss of certain genes.

2. Insertions occur when a part of a chromatid breaks off and attaches to its sister

chromatid; results to duplication of genes on the same chromosome.

(A) This is a portion of a chromatid (far from the centromere) prior to deletion. (B) This is a chromosomal segment which will be deleted. (C) This is the same chromatid but with deleted parts.

A

C

(A) This is the first sister chromatid. (B) This is a part of chromatid A that breaks off from the chain. C) This is the chromatid with attached broken chromosomal fragment B from its sister chromatid.

A

B

B

C

B

insertion


3. Inversions occur when part of a chromosome breaks off and is reinserted backwards.

4. Translocations occur when part of one chromosome breaks off and is added to a

different chromosome. b

(A) This is a part of a chromatid. (B) This is a part of the chromatid that breaks off the chain and reverses in orientation. (C) This is the same chromatid but with the inverted chromosomal segment.

A CB

B

(AB) This a chromosome fragment that breaks off into two: segment A and segment B. (ab) This is another chromosome fragment that breaks off into two: segment a and segment b (Ab) After translocation, segment A attaches with segment b. (aB) After translocation, segment a attaches with segment B.


Genome Organization and Expression in Eukaryotes Important terms Genome refers to the totality of an organism’s genetic material..

Chromatin is the collective mass of dispersed genetic material composed of DNA and protein Eukaryotes are organisms with membrane-enclosed nucleus and membrane-enclosed organelles;

e.g., protests, plants, fungi, and animals. Gene expression refers to the transcription and translation of genes into products that carry out

its role in the organism. This occurs during interphase stage of the cell cycle.

Levels of Chromatin Packing This is a series of diagrams that show a current model for the progressive stages of DNA coiling and folding, which culminate in the highly condensed metaphase chromosome.

DNA nucleosomes 30-nm chromatin fiber looped domains metaphase chromosome

• Nucleosomes, or the “beads on a string.” DNA, together with histones, forms “beads on a string,” which consist of nucleosomes in an extended configuration. Each nucleosome has two molecules each of four types of histone. The fifth histone (called H1) may be present in the DNA adjacent to the “bead.”

• 30-nm chromatin fiber is a tightly wound coil with six nucleosomes per turn.


• Looped domains of 30-nm fibers are visible here because a compact chromosome has been experimentally unraveled.

• Metaphase chromosome. These multiple levels of chromatin packing form the compact chromosome, visible at metaphase.

Key points about the control of gene expression in eukaryotes:

• The assorted cell types of a multi-cellular organism express different genes.

• The physical organization of chromatin makes certain genes accessible for expression and other genes unavailable.

• For genes that are available for expression, regulatory opportunities subsist at each step in the pathway from gene to functional protein.

• Control of transcription is especially significant in determining which genes are expressed; in eukaryotes, the selective binding of transcription factors to enhancer sequences in DNA stimulates transcription of specific genes.

• The regulatory activity of some of these DNA-binding proteins is susceptible to certain hormones and other chemical signals.

Chemical modification or relocation of DNA

1. Gene amplification may happen in some tissues during development. 2. The cells of some species show selective gene loss, in which entire chromosomes or parts

of chromosomes of specific cells are discarded. 3. Rearrangements of DNA can activate or inactivate specific genes. By transferring from

one place to another within the genome, transposes can affect gene expression. 4. In vertebrates, a rearrangement and selective deletion of DNA segments in differentiating

B lymphocytes accounts for antibody variety. 5. The attachment of methyl groups to DNA may reduce transcription of that DNA.


Mendelian Genetics Gregor Mendel

• During the1860s, Gregor Mendel developed a particulate theory of inheritance based on his experiments on garden peas.

• He demonstrated that parents pass on to their offspring discrete genes that retain their identity generation after generation.

Important terms Hybridization is the mating or crossing of two varieties. P (parental) generation are comprised of the true breeding parents. F1 (1st filial) generation is the P generation’s hybrid offspring. F2 (2nd filial) generation is the generation after the F1 generation self-pollinates. Alleles is the alternative versions of a gene. Dominant allele is the allele fully expressed in the organism’s appearance. Recessive allele, allele that has no noticeable effect on the organism’s appearance. Homozygotes are organisms having a pair of identical alleles for a character. Heterozygotes are organisms having different alleles for a character. Phenotype is an organism’s appearance. Genotype is an organism’s genetic makeup.

Mendel’s Law of Segregation

The two alleles for a character are packaged into separate gametes. Mendel’s Law of Independent Assortment

Each pair of alleles segregates into gametes independently. Other Observations by Mendel

• Rule of multiplication: The probability of a compound event is equal to the product of the separate probabities of the independent single events.

• Rule of addition: The probability of an event that can occur in two or more independent ways is the sum of the separate probabilities.

• Some heterozygous genotypes result in incomplete dominance. Such individuals have an appearance that is intermediate between the phenotypes of the two parents.

• In codominance, a heterozygous organism expresses both phenotypes of its two alleles. • Many genes have multiple alleles. • Pleiotropy is the ability of a single gene to affect multiple phenotypic traits. • In epistasis, one gene interferes with the expression of another gene. • The environment also influences quantitative characters.


Protein Synthesis Transcription. Messenger ribonucleic acid (mRNA) is made during the process of transcription.

• The process of transcription begins as enzymes unzip the molecule of DNA, just as they do during DNA replication.

• As the DNA molecule unzips, free RNA nucleotides pair with complementary DNA nucleotides on one of the DNA strands. Thus, if a sequence of bases on the DNA strand were AGC TAA CCG, the sequence of bases on the RNA strand would be UCG AUU GGC.

• When the process of base pairing is completed, the mRNA molecule breaks away as the DNA strands rejoin. The mRNA leaves the nucleus and enters the cytoplasm.

Genetic Code This code is used to convert the language of the mRNA into the language of proteins. There are 20 different amino acids, but mRNA contains only four types of bases: Adenine, Guanine, Uracil and Thymine. Each set of three nitrogen bases in mRNA representing an amino acid is called a codon.


Translation: From mRNA to protein

• As translation begins, the starting end of the mRNA strand attaches to a ribosome. Then the transfer RNA (tRNA) molecules, each carrying a specific amino acid, approach the ribosome. When a tRNA anticodon pairs with the first mRNA codon, the two molecules temporarily join together.

• Usually, the first codon on mRNA is AUG, which codes for the amino acid methionine. AUG signals the start of protein synthesis. When this signal is given, the ribosome slides along the mRNA to the next codon.

• A new tRNA molecule carrying an amino acid pairs with the second mRNA codon.

• When the first and second amino acids are in place, an enzyme joins them by forming a peptide bond between them.

• As the process continues, a chain of amino acids is formed until the ribosome reaches stop codon (UAA or UAG) on the mRNA strand.


QUIZ

Heredity and Genetics Fill in the blanks.

______________ has the complete instructions for manufacturing all the proteins for an organism. The two chains of nucleotides in a DNA molecule are held together by ____________________ between the bases. There are four nitrogen bases (carbon ring structures that contain one or more atoms of nitrogen): _____________ (A), ____________ (T), ______________ (C), and ______________ (G). ___________________ is the process of making copies of DNA.

DNA _________________ refers to any change in the DNA sequence. ___________________ mutation is a type of DNA mutation wherein a single base is added or deleted from the DNA. Identify the following types of chromatin mutations:

_________ __________________________ _________ ________________________


In the 1860s, ____________________ developed a particulate theory of inheritance based on his experiments on garden peas. ________________ are organisms having different alleles for a character.

__________________ refers to an organism’s appearance, while __________________ is the organism’s genetic makeup.

Mendel’s Law of _________________ states that the two alleles for a character are packaged into separate gametes.

In _______________, a heterozygous organism expresses both phenotypes of its two alleles. In ________________, one gene interferes with the expression of another gene.

_____________________ is created during the process of transcription. Each set of three nitrogen bases in mRNA representing an amino acid is called a ____________.

Usually, the first codon on mRNA is AUG, which codes for the amino acid ______________.

Identify the following levels of chromatin packing:

____________ _____________ _________________ ________________ ______________________

The attachment of ______________ to DNA may reduce transcription of that DNA.


DNA “fingerprints” obtained from ________________ analysis of blood, hair, or other materials found at the scenes of violent crimes as evidence in court trials. In agriculture, ________________ plants and animals (organisms containing genes from other species) are being designed to improve productivity and food quality.

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