Download Review: Genetics

Review:
Reproduction & Genetics
• Why do organisms reproduce?
– For the continuation of the species
• How do organisms reproduce?
– Sexual reproduction: two organisms produce a
new unique organism
– Asexual reproduction: one organism produces a
new nearly identical organism = no variability!
Cell Division
• Before a cell becomes too large, it divides to form two cells.
• The two new cells are called daughter cells.
• The process by which the cell divides into two new daughter
cells is called cell division.
• At this very moment, group of cells in your body are growing,
dividing, and dying.
• Worn out skin is being replaced and bruises are healing.
• Red blood cells are being produced in your bones at a rate of 2
to 3 billion to replace those that wear out.
Cellular Reproduction
• Reproduction – the life process by which living things produce
other living thing of the same species
• It is necessary for the survival for the species
• Two types of Reproduction through cell division:
– Sexually reproducing organisms go through mitosis and meiosis
– Asexually reproducing organisms only go through mitosis
Chromosomes
• Pass genetic information
from one generation of
cells to the next
• Made up of DNA (which
carries the cell’s coded
genetic information) and
proteins
• The cells of every
organisms have a specific
number of chromosomes
– Human somatic (body) cells
= 46 chromosomes
– Human gametes (sex cells) =
23 chromosomes
Asexual reproduction
• Your body (somatic) cells
– Cellular asexual reproduction (mitosis and
cytokinesis): Organisms with eukaryotic cells use
mitosis and cytokinesis to create cells with the same
genetic information (DNA) as the parent cell.
• Some organisms
–
–
–
–
–
Binary fission
Budding
Sporulation (spore formation)
Regeneration
Vegetative Propagation
Sexual Reproduction
• What is an inheritance?
– Something passed from one generation to the next.
• How is it determined?
– Your genes from your parents!
• Since the hereditary material comes from two parents it
resembles both parents in some ways, but is also different
from both in others.
• It has all the characteristics of its species, but at the same
time has its own individual characteristics that distinguish
it from all other members of that species.
• Genetics = The branch of biology that is concerned with the
ways in which hereditary information is transmitted from
parents to offspring.
Genes
• Hereditary information is
contained in genes, located
in the chromosomes of
each cell.
• An inherited trait of an
individual can be
determined by one or by
many genes, and a single
gene can influence more
than one trait.
• A human cell contains many
thousands of different
genes in its nucleus.
Dominant vs. Recessive
• An organism with a dominant allele for a
particular trait will always have that form
– The characteristic shows up
• An organism with a recessive allele for a
particular trait will have that form only when the
dominant allele for the trait is not present
– The characteristic only shows up when the dominant
allele is not present, otherwise it is carried
• Alleles are separated (segregated) during gamete
(sex cell) formation.
Mendel’s Principles
• Inheritance is determined by genes passed from
parents to offspring
• Some forms of genes are dominant and others are
recessive
• Each offspring has two copies of a gene (alleles),
one from each parent because they are segregated
during game formation
• The allele for different genes usually segregate
independently of one another during gamete
formation
Diploid cells
• Chromosomes come from both the male parent
and female parent
• Homologous pairs: each of the chromosomes
coming from one parent have corresponding
chromosomes from the other parent
• Diploid: a cell that contains both sets of
homologous chromosomes = “two sets” (2N)
– Diploid cells contain two complete sets of
chromosomes and two complete sets of genes
– Human somatic (body) cells have 46 chromosomes or
23 homologous pairs
Haploid cells
• Haploid: contain only one set of chromosomes and
one set of genes = “one set” (N)
• Gametes of sexually reproducing organisms are haploid
containing one complete sets of chromosomes and
one complete sets of genes
• Human gametes have
23 chromosomes
• Sperm (23) + Egg (23) = Zygote (46)
• How are haploid gamete
produced from diploid cells?
Meiosis
 The process of
reduction division in
which the number of
chromosomes per cell
is cut in half through
the separation of
homologous
chromosomes in a
diploid cell
 The four daughter
cells contain haploid
(N) chromosomes
Importance of crossing-over
• However, crossing-over sometimes separates gene that are usually
found on the same chromosome, so genes may not be linked
together forever!
• Crossing-over is soooo important because it helps generate genetic
diversity – new combinations of allele are constantly produced
• Increasing the variability of a species increases the possibility that
some individuals of that species will be better adapted than others
to survive both short-term and long-term changes in the
environment.
Mitosis vs. Meiosis
• Mitosis – produces
2 genetically
identical diploid
cells
• Meiosis – produces
4 genetically
different haploid
cells
DNA
• Genes are made of DNA = deoxyribonucleic acid
• DNA codes for the function of genes
• Its a long molecule made of units called
nucleotides
• Each nucleotide is made of 3 basic parts:
– A 5-carbon sugar called deoxyribose
– A phosphate group
– A nitrogenous base (There are 4 kinds…)
A (Adenine)
G (Guanine)
Purines
T (Thymine)
C (Cytosine)
Pyrimidines
A Single
DNA Nucleotide
Phosphate
Group
Deoxyribose
Sugar
Nitrogenous
Base
DNA Structure
Nitrogenous Base
Weak Hydrogen Bonds
Deoxyribose
Sugar
Structure of DNA
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Go to
Section:
Figure 12-10 Chromosome
Structure of Eukaryotes
Section 12-2
Eukaryotic DNA
Nucleosome
Chromosome
DNA
double
helix
Coils
Supercoils
Histones
• DNA is found in the nucleus in chromosomes (the number of
chromosomes varies widely of different species)
• DNA is very long!... but it is highly folded packed tightly to fit into the cell!
Go to
Section:
– For example, a human cell contains more than 1 meter of DNA made of more
than 30 million base pairs!
Eukaryotic Chromosomes
• Contain DNA and proteins called histones
• Tightly packed DNA and proteins form
chromatin
• During mitosis, the chromatin condenses to
form tightly packed chromosomes
DNA Replication
• The process of making a copy of the DNA
• Occurs inside the nucleus of the cell
• Occurs when the cell is going to divide so
each resulting cell will have a complete set
of DNA
• During DNA replication, the DNA
separates into two strands, then produces
two new complementary strands following
the rules of base pairing.
• Each strand serves as a template, or
model, for the new strand.
• Replication occurs in both directions
• The site where separation occurs is called
the replication fork
DNA Replication
• The two strands of DNA unwind or “unzip”
breaking the hydrogen bonds and separating.
Then each strand becomes the guide or
“template” for the making of a new strand.
• A protein called an enzyme called DNA
polymerase breaks the nitrogen base bonds and
the two strands of DNA separate, polymerizes
individual nucleotides to produce DNA and
“proof reads” the new DNA.
• The bases on each strand pair up with new
bases found in the cytoplasm
• Then the sugar and phosphate groups form the
sides of each new DNA strand
• Each new DNA molecule contains an original
DNA strand and a new DNA strand
DNA Replication
New strand
Original
strand
DNA
polymerase
Growth
DNA polymerase
Growth
Replication fork
Replication fork
New strand
Go to
Section:
Original
strand
Nitrogenous bases
Mutations
• Changes in the DNA sequence the affect genetic information
• Mistakes occur every now and then
• There are many different types of mistakes:
– Inserting the wrong base
– Deleting a base
– Skipping a base
• Gene mutations result from changes in a single gene
• Chromosomal mutations involve changes in whole
chromosomes
Chromosomal Mutations
• There are four chromosomal mutations:
– Deletion: loss of all or part of a chromosome
– Duplication: segment of a chromosome is repeated
– Inversion: orient part of chromosome in reverse direction
– Translocation: part of one chromosome breaks off and
attaches to another, non-homologous, chromosome.
Deletion
Duplication
Inversion
Translocation
How are genes expressed?
• Genes are coded DNA instructions that control
the production of proteins within the cell.
• The 1st step in decoding the DNA is to copy
part of the nucleotide sequence into RNA
• RNA = ribonucleic acid
• RNA assembles amino acids
into proteins
RNA
• RNA consists of a long chain of nucleotides
(like DNA)
– A sugar called ribose
– A phosphate group
– A nitrogenous base
Adenine (A)
Uracil (U) … not Thymine (T)
Cytosine (C)
Guanine (G)
• RNA is single-stranded
RNA Nucleotide
Phosphate
Group
Nitrogenous
Base
Ribose
Sugar
RNA Structure
Nitrogenous Base
Ribose Sugar
Types of RNA
• Messenger RNA copies instructions in genes and serves as a
“messenger” from the DNA to the ribosome
• Ribosomes make proteins
• Ribosomal RNA passes through the ribosome
• Transfer RNA transfer amino acids to the ribosome
How is RNA made?
• RNA is made by transcription: DNA to RNA
• Transcription uses an enzyme RNA polymerase
• During transcription, RNA polymerase binds to DNA and
separates the DNA strands, RNA polymerase then uses one
strand of DNA as a template (stencil) from which nucleotides
are assembled into a strand of RNA
• For example:
DNA:
RNA:
ACTGTGGACCT
UGACACCUGGA
TRANSCRIPTION
Figure 12–14 Transcription
Section 12-3
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
RNA
Go to
Section:
DNA
How are proteins made?
• Proteins are made by translation: RNA to protein
• During translation, the cell uses information from mRNA to
make proteins.
• mRNA instructs amino acids on tRNA to join together in the
ribosome containing rRNA
• Remember: Proteins are chains of amino acids called
polypeptides
• The order of the amino acids and shape of the chain determines
the properties of the protein
• The instructions for making different
amino acids are in the mRNA =
the genetic code
• The genetic codes is read 3 letters at a time,
• so each “word” is 3 bases long = codon
Figure 12–18 Translation
Section 12-3
Nucleus
Messenger RNA
Messenger RNA is transcribed in the nucleus.
Phenylalanine
tRNA
The mRNA then enters the cytoplasm and attaches
to a ribosome. Translation begins at AUG, the start
codon. Each transfer RNA has an anticodon whose
bases are complementary to a codon on the mRNA
strand. The ribosome positions the start codon to
attract its anticodon, which is part of the tRNA that
binds methionine. The ribosome also binds the
next codon and its anticodon.
Ribosome
Go to
Section:
mRNA
Transfer RNA
Methionine
mRNA
Lysine
Start codon
Figure 12–18 Translation (continued)
Section 12-3
The Polypeptide “Assembly Line”
The ribosome joins the two amino acids—
methionine and phenylalanine—and breaks the
bond between methionine and its tRNA. The tRNA
floats away, allowing the ribosome to bind to
another tRNA. The ribosome moves along the
mRNA, binding new tRNA molecules and amino
acids.
Lysine
Growing polypeptide chain
Ribosome
tRNA
tRNA
mRNA
Completing the Polypeptide
mRNA
Ribosome
Go to
Section:
Translation direction
The process continues until the ribosome reaches one
of the three stop codons. The result is a growing
polypeptide chain.
Genetic Engineering
• Genetic engineering changes the arrangement of
DNA that makes up a gene.
• Genes can also be inserted into cells to change how
the cell performs.
• For example, large volumes of medicines, such as insulin,
can be produced or plants resistant to diseases can be
developed.
Uses of Genetic Engineering
•
•
•
In the past, people breed for organisms with desired traits by selective
breeding
Now people can insert genes (DNA) into cells to produce organisms with
those same desired traits by genetic engineering (Cell Transformation)
• Gene therapy is a form of genetic engineering that inserts a normal
allele into a virus that attacks a target cell and inserts the normal allele
into the body.
Cloning is the process of making a new identical copy of an organism
from a single adult cell. Cloning can occur naturally as twins, or to
genetically engineer plants and animals, endangered or extinct species, a
deceased pet or human, or stem cells.
• Stem cells are the cells that all of your cells “stem” from. Stem cells
can be used to determine the function of specific genes, manipulate
genes, or make new cells or tissue to treat injuries or diseases.
Transforming Bacteria
• Bacteria can be transformed using recombinant DNA.
• Foreign DNA joins to a small circular DNA called a plasmid, which are
naturally found in some bacteria.
Pedigrees are used to study how traits are passed from one
generation to the next.
However, most human traits are impossible to trace as
single genes. Remember:
Many human traits are polygenic = many genes control a single trait
Phenotypes are influenced by genotypes and the environment.
Karyotype = picture of organized chromosomes
Human cells contain 46 chromosomes (23 pairs)
44 chromosomes are autosomal chromosomes or autosomes
2 chromosomes are known as sex chromosomes, because they
determine an individual’s sex.
Females have two X chromosomes (46XX)
Males have one X and one Y chromosome (46XY)
Sex-linked Genes
• Genes located on the X or Y
chromosomes are said to be
sex-linked.
– Many sex-linked genes are found
on the X chromosome, the smaller
Y chromosome contains only a
few genes.
– Since males have just one X
chromosome, X-linked alleles are
expressed in males, even if their
recessive
• Colorblindness
• Hemophilia
• Duchenne Muscular Dystrophy
Figure 14-13 Colorblindness
Section 14-2
Father
(normal vision)
Colorblind
Normal
vision
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Daughter
(carrier)
Son
(colorblind)
Mother
(carrier)
Go to
Section:
Human Genes
• The human genome includes tens of thousands of genes and
the DNA sequence on these genes determines many
characteristics.
• Gene mapping is the process of identifying the trait each gene
is responsible for on each chromosome.
• Since no two individuals have the exact same genome,
biologist can use DNA fingerprinting to identify individuals
– For example, if blood, sperm or hair is found at a crime
scene, DNA from the tissue can be cut using restriction
enzymes and fragments can be separated using gel
electrophoresis, resulting in a unique pattern that can be
compared to a suspect’s DNA
Figure 14-18 DNA Fingerprinting
Section 14-3
DNA Fingerprinting
Restriction enzyme
Chromosomes contain large
amounts of DNA called repeats
that do not code for proteins.
This DNA varies from person to
person. Here, one sample has
12 repeats between genes A
and B, while the second
sample has 9 repeats.
Go to
Section:
Restriction enzymes are used
to cut the DNA into fragments
containing genes and repeats.
Note that the repeat fragments
from these two samples are of
different lengths.
The DNA fragments are
separated according to size using
gel electrophoresis. The
fragments containing repeats are
then labeled using radioactive
probes. This produces a series of
bands—the DNA fingerprint.
Gene Therapy
• Gene therapy = an absent or faulty gene is replaced by a
normal, working gene, but it can’t be inherited unless a
reproductive cell is altered!
– Some researchers insert a DNA fragment containing a
replacement gene into viral DNA, and then infect the
patient with the modified virus, which should carry the
gene into cells and correct the genetic disorder.