TEKS B6.A: Identify components of DNA, and describe

how information for specifying the traits of an organism is

carried in the DNA.

The components of the DNA are: deoxyribose sugar,

phosphate group, nitrogen base. The three components are

arranged in a molecule called nucleotide. Nucleotides join

together to form the DNA.

The DNA has two sides which are ANTIPARALLEL, which

means they are oriented in opposite direction. The nitrogen

bases are held by HYDROGEN BONDS. In DNA, Adenine

always pairs up with Thymine and Guanine always pairs up with

Cytosine.

The DNA contains the codes to build the structure of

organisms. Each structure corresponds to a part of the DNA

called gene. The one gene one structure hypothesis states

that each kind of protein, each kind of enzyme, and each kind

of hormone in an organism has a corresponding gene in the

organism’s DNA.

The table above shows a comparison of the amount of

nitrogen bases and genes in the DNA of the specified

organisms.

TEKS B6.B: Recognize that components that make up the

genetic code are common to all organisms.

Animals, plants, bacteria and

all other living things have

DNA. Viruses although are not

considered living have DNA

too. The basic components of

the DNA is the same – made up

of the FOUR NUCLEOTIDES,

(A, T, C, G).

From the table above, we can see that the human, mouse, thale

cress, round worm, fruit fly, yeast, bacteria, and virus have

the same group of nitrogen basis in their DNA, they only

differ on the amount and on how they are arranged.

TEKS B6.C: Explain the purpose and process of

transcription and translation using models of DNA and RNA

Gene expression is the process by which genetic codes are

used to create physical structures. The physical structures

are proteins. Gene expression has two steps – transcription

and translation.

Transcription – a strand of the DNA is copied. The copy is

called RNA. It occurs in the nucleus.

Why is transcription important? – The DNA contains the code

to build proteins. Proteins are constructed in the cytoplasm.

DNA cannot get out of the nucleus. To use the DNA code, it

has to be copied into RNA then the RNA goes out of the

nucleus and is used in the construction of proteins.

There are three types of

RNA

a. Messenger RNA or

mRNA – serves as

template in the

assembly of proteins

b. Transfer RNA or

tRNA – serves as

carriers of amino acids

to be assembled as

proteins

c. Ribosomal RNA or

rRNA – combines with

the ribosome that

assembles proteins.

Note:

Ribosome is an organelle that synthesizes proteins.

Amino acids are the building blocks of proteins. There

are 20 different types of amino acids.

Proteins or polypeptides are used as parts to build

many structures in organisms – bone, blood, skin,

muscles, leaves, stems, fruits etc.

Translation – the building of proteins. It occurs in the

cytoplasm.

How are proteins assembled? – each tRNA carry an amino acid.

The tRNAs bring the amino acids to the ribosomes. The

ribosome assembles the amino acids that correspond to the

codes in the mRNA that is being used by the ribosome

starting from the 5’ going through 3’.

Each three letter combination in the mRNA is called

CODON. Each codon corresponds to amino acid.

The three letter combinations in the tRNA that pair with

the codons are called ANTICODONS.

The codon chart shows the corresponding amino acids.

For example:

DNA Codon Anti

codon

Amino acid

CCA GGU CCA Glycine (GLY)

AGT UCA AGU Serine (SER)

CTC GAG CUC Glutamate (GLU)

CAC GUG CAC Valine (VAL)

ATT UAA AUU Stop codon (STOP)

TAC AUG UAC Start codon or Methionine

(MET)

TEKS B6.D: Recognize that gene expression is a regulated

process.

Gene expression is the process by which genetic codes are

used to create proteins. Gene expression has two steps –

transcription and translation.

Gene expression is a regulated process. The DNA contains

nitrogen base sequences that are inchrge of controlling how

the genes are expressed. Some of the controlers may be

affected by environmental factors. This is why gene

expression is affected by the organism’s environment.

Gene regulation can be during:

A. Transcription

B. Translation

C. Post-Translation

TEKS B6.E: Identify and illustrate changes in DNA and

evaluate the significance of these changes

DNA mutation – change in the arrangement of nitrogen

bases in the DNA. The change may be caused by

substitution, insertion, deletion, or frameshift.

Effects of mutation:

1. No effect

2. Harmful effect – like cancer, trisomy, sickle cell

anemia

3. Helpful – resistance to diseases, acquisition of

adaptive traits

Causes of mutation:

1. DNA fails to copy accurately

2. Exposure to some chemicals or radiation

Note:

1. DNA mutation is a natural and common process.

Cells have the ability to repair DNA damages.

In some cases though, damages may not be

repaired completely.

2. DNA mutations in somatic cells affect ONLY

the organism. DNA mutations in gametes are

passed on to and affects even the offspring.

TEKS Recognize the significance of meiosis to sexual

reproduction.

Cells in an organism may be

grouped into two - the

somatic cells and the

gametes or (sex-cells).

Gametes are the sperm and

ovum or egg.

Meiosis is the cell division

by which sperm and egg are

prodcued.

Importance of meiosis:

It allows the creation

of haploid cells making

sexual reproduction

possible.

Note:

Haploid – one set of

chromosomes

Diploid – two sets of

chromosomes

Homologous chromosomes

– chromosomes that have

the same set of genes

but may have different

versions of the genes.

Meiosis is important in sexually reproducing organisms.

During fertilization, a sperm and ovum fuse. Meiosis allows

the formation of haploid cells that will fuse and form diploid

cells during fertilization.

Crossing over during metaphase I allows more genetic

variation or diversity.

Human somatic cells have 46 chromosomes

Human sperm and egg cells have 23 chromosomes

TEKS B6.H: Describe how techniques such as DNA

fingerprinting, genetic modifications and chromosomal

analysis are used to study the genomes of organisms.

DNA fingerprinting is the process of analyzing and

comparing DNA samples. Individual organisms have unique

DNA fingerprint except for identical twins.

Genetic modification or ginetic engineering – the process of

inserting desired genes or removing unwanted genes in an

organism’s DNA. Genes from other organisms can be used like

from one plant to another.

Usually done to improve an organism like making it more

resistant to diseases, to high temperature or to produce

more fruits or grains.

Karyotype shows the number and visual appearnce or position

of chromosomes of an organism. Chromosomal analysis or

karyotype anylysis is the comparison of chromosomal number

and appearnce of a karyotype. It is an important strategy

used to study genetic abnormalities.

As compared to:

The human genome project is the sequencing of proteins in

humans. They identified the nitrogen base sequences in

relation to their functions.

TEKS B6.F: Predict possible outcomes of various genetic

combinations such as monohybrid crosses, dihybrid crosses

and non‐Mendelian inheritance.

Genetics is the branch of biology that deals with heredity.

Research on genetics began with Gregor Mendel, who

experimented on pea plants in the 1800s.

Gene – a segment of DNA that codes for a protein

Allele - alternate form of a gene

Gene for allele

Flower color violet white

Seed shape round wrinkled

Stem size tall short

Mendel’s experiment- crossed pea plants that had different traits:

tall x short purple x white, round x wrinkled seeds

P (Parental Generation) True breeding plants F1 (First Filial) offspring of the P generation --> displayed a single trait F2 (Second Filial) offspring of F1 generation

Allele can be dominant or recessive

Dominant - Allele that is expressed

Recessive - Allele that is hidden

Homozygous - having two of the same allele, true-

breeding or pure breed

AA – homozygous dominant

Aa – homozygous recessive

Heterozygous - two different alleles (Aa); hybrid

Dominant alleles – upper case letters symbol

Recessive alleles – lower case letters symbol

Genotype - the organism’s alleles

Phenotype - the physical appearance

Patterns of Inheritance

1. Law of dominance – recessive trait is covered by

dominant trait

2. Law of codominance – two dominant traits show up in

the organism/s phenotype at the same time

3. Law of incomplete dominance – two traits that are not

dominant will produce a third phenotype, a blending of

the two traits

4. Law of segregation – the alleles of a gene segregate

during gamete (sperm or egg) formation

5. Law of independent assortment - each pair of allele

segregates independently of other pairs of alleles

6. Sex-linked traits – some genes are located on the X or

Y chromosome and they always go with being a male or

female

7. Traits with multiple alleles – a trait is controlled by

more than two alleles

8. Polygenic Traits – traits are controlled by groups of

several genes

9. Pleiotropy – a gene affects more than one unrelated

traits

Crosses and genotype and phenotype probability

Monohybrid cross – cross involving only one trait

Dihybrid cross – cross involving two traits

Genotype ratio: Phenotype ratio: YY – 0 yellow – 4 Yy – 4 green – 0 yy – 0

4:0:0 4:0

Yellow – 100 % Green – 0%

Homozygous – 0% Heterozygous – 100%

Phenotype ratio: Yellow and round – 16 Yellow and wrinkled - 0 Green and round – 0 Green and wrinkled – 0

16 : 0 : 0 : 0 Yellow and round – 100% Yellow and wrinkled – 0% Green and round – 0% Green and wrinkled – 0%