Download Competency 5 Heredity

Competency 5
Heredity
The Structure of DNA
 DNA is a very long polymer.
 The basic shape is a double
helix. A double helix looks
like a twisted ladder.
 In the double-helix model of
DNA, the two strands twist
around each other like spiral
staircases.
Chromosomes
 Chromosomes are a single strand of DNA tightly
coiled around a protein called a histone.
 A section of DNA that carries the information to
make one protein is called a gene.
The Structure of DNA
 DNA is a nucleic acid made up of nucleotides
(monomers) joined into long strands, or chains, by
covalent bonds.
 Each nucleotide is composed of 3 parts:
Sugar – DEOXYRIBOSE
Phosphate group
Nitrogen bases
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
The Structure of DNA
 DNA has four kinds of nitrogenous
bases: adenine (A), guanine (G),
cytosine (C), and thymine (T)
 Hydrogen bonds form between A
and T base pairs as well as between C
and G base pairs.
 The nitrogenous bases stick out
sideways from the nucleotide chain.
 The nucleotides can be joined
together in any order, meaning that
any sequence of the bases is possible.
The Structure of DNA
 Erwin Chargaff analyzed the amount of
adenine, guanine, thymine, and
cytosine in the DNA of various species.
 He found that the amount of guanine
nearly equals the amount of cytosine,
and the amount of adenine nearly
equals the amount off thymine within a
species.
 Adenine and guanine are purine bases
 Cytosine and thymine are pyrimidine
bases.
Base-Pairings
 Purines only pair with pyrimidines.
 Three hydrogen bonds are required to bond guanine
and cytosine.
 Two hydrogen bonds are required to bond adenine
and thymine.
Practice #1
 DNA complementary base-pairing practice – Fill in the
blanks to create complementary strands of DNA
 Strand 1
A
__
T
G
A
__
__
G
Strand 2
__
T
__
__
__
T
C
__
Answers
Strand 1
Strand 2
A
T
A
T
T
A
G
C
A
T
A
T
G
C
G
C
Practice #2
 Percentage of Bases in Four Organisms
Source of DNA
A
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8
What does the data suggest to you?
Answer
The data suggests that the percentages of adenine
and thymine are almost equal in any sample of DNA.
The same thing is true for the percentages of cytosine
and guanine.
DNA Replication
 Before a cell divides, it duplicates its DNA in a copying
process called replication.
 DNA replication is a process that ensures that each
resulting cell has the same complete set of DNA molecules.
 During replication, the DNA molecule separates into two
strands and then produces two new complementary strands
following the rules of base pairing.
 Each strand of the double helix of DNA serves as a template,
or model, for the new strand.
Replication Fork
Original Strand
New Strands
DNA Polymerase
Transcription
Comparing RNA and DNA
RNA
DNA
Sugar – Ribose
Sugar: Deoxyribose
Single-stranded
Double-stranded
Uracil (A,G,C,U)
Thymine (A,G,C,T)
Types of RNA
 Messenger RNA (mRNA) carries the genetic
message of DNA from the nucleus to other parts of
the cell.
 Ribosomal RNA (rRNA) forms parts of
ribosomes, the cell’s protein factories.
 Transfer RNA (tRNA) transfers each amino acid
to the ribosome as it is specified by the coded
messages in mRNA.
Three Main Types of RNA
 messenger RNA (mRNA) carries
copies of instructions for
assembling amino acids into
proteins.
 ribosomal RNA (rRNA) Ribosomes
are made up of proteins and
ribosomal rRNA.
 transfer RNA(tRNA) transfers each
amino acid to the ribosome.
Protein Synthesis
 Proteins are made in a two step process:
-Part One: Transcription in the nucleus
- Part Two: Translation happens at the
ribosome
Transcription
 Genes contain coded DNA instructions that tell cells how
to build proteins.
 The first step is decoding the genetic instructions is to
copy part of the base sequence from DNA to RNA.
 Transcription: Since DNA cannot leave the nucleus;
free nucleotides use a strand of DNA to make mRNA
(messenger RNA) inside the nucleus. The mRNA strand
then leaves the nucleus and travels into the cytoplasm.
 mRNA snakes out of the nucleus into the cytoplasm and
uses the base sequence copied from DNA to direct the
production of proteins.
Transcription
Codon
 These bases form a “language,” or genetic code,
with just four letters: A, C, G, and U.
 Each three-letter “word” in mRNA is known as a
codon.
 A codon consists of three consecutive bases that
specify a single amino acid to be added to the
protein chain.
Anticodons
 Anticodons are the three unpaired bases of tRNA.
These bases are complementary to mRNA codons.
Translation
 Translation occurs at the ribosome. A three letter
anti-codons on tRNA codes for specific amino acids at
the top of tRNA.
 There are 64 different combinations or codons, but
only 20 amino acids.
 When the amino acids link together in a peptide bond,
they produce proteins. Genes directly control the
synthesis of proteins.
https://www.youtube.com/watch
?v=41_Ne5mS2ls
Reading Codons
Suppose you wanted to determine which amino acid is encoded by the CAU
codon.
 Find the first base “C” in
the left column.
 Find the second base “A”
in the top row, Find the
box where these two
letters intersect.
 Find the third base “U” in
the right column. Find
where all three intersect.
 CAU codes for His
(histadine)
Codon Wheel: Read 3 letters at a time, inside to
outside.
Gel Electrophoresis and
DNA Fingerprinting
 Small DNA samples can be obtained from blood,
hair, skin, or semen
 Technology that separates DNA fragments so they
can be analyzed into a DNA fingerprint
 It is used to find the similarities and differences in
genomes of different organisms, identify parents,
catch criminals, because no two people, except
identical twins, have the exact same DNA
Who is guilty?
Who is guilty?
Who are the parents?
PCR: Polymerase Chain Reaction
 The polymerase chain reaction (PCR) is a biomedical
technology in molecular biology used to amplify a
single copy or a few copies of a piece of DNA across
several orders of magnitude, generating thousands to
millions of copies of a particular DNA sequence.
 https://www.youtube.com/watch?v=0HCWmD7Mv
8U
Selective Breeding
 Selective breeding allows only those organisms with
desired characteristics to produce the next
generation.
 Humans use selective breeding to pass desired traits
on to the next generation of organisms.
 Nearly all domestic animals and most crop plants
have been produced by selective breeding.
Recombinant DNA


Most DNA molecules are too large to be analyzed, so biologists cut
them into smaller fragments using restriction enzymes.
Recombinant DNA is used in producing insulin and producing growth
hormones from different sources. examples: chickens that grow faster
and make human insulin
Other Important Terms
 Genetic Engineering- making changes in an
organism’s DNA
 Transformation- the process used to place
recombinant DNA back into a living organism
 Transgenic- term used to describe an organism that
contains the DNA from a different organism using
recombinant example: disease resistant plants
 DNA Reproductive cloning – process of creating an
organism that is genetically identical to a donor cell
Genetic Terminology
 Traits are any characteristic that can be passed from
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

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parent to offspring.
Heredity is the passing of traits from parent to
offspring.
Genetics is the study of heredity.
Monohybrid cross is a cross involving a single trait
(ex: flower color).
Dihybrid cross is a cross involving two traits (ex:
flower color and plant height).
Alleles are two forms of a gene (two letter combination
of recessive and dominant).
Genetic Terminology
 Genotype is a gene combination for a trait (ex: RR, Rr, rr).
 Phenotype is the physical feature resulting from a genotype
(ex: red, yellow)
 Genotypes and Phenotypes in flowers:
Genotype of alleles:
R = red flower
r = yellow flower
 All genes occur in pairs, so 2 alleles affect a characteristic.
 Possible combinations are:


Genotypes RR
Phenotypes Red
Rr
Red
rr
yellow
Genetic Terminology
 Dominant is the stronger of the two genes
expressed in the hybrid; represented by a capital “R.”
 Recessive is a gene that shows up less often in the
cross; represented by a lower “r.”
 Homozygous genotype is a gene combination
involving 2 dominant or 2 recessive genes (ex: RR or
rr); also called pure.
 Heterozygous genotype is a gene combination of
one dominant and one recessive allele (ex: Rr); also
called hybrid.
Punnett Squares
 Punnett squares use mathematical probability to
help predict the genotype and phenotype combinations
in genetic crosses.
 One of the best ways to predict the outcome of a
genetic cross is by drawing a simple diagram known as
a Punnett square.
 Punnett squares allow you to predict the genotype and
phenotype combinations in genetic crosses using
mathematical probability.
How to Make a Punnett Square
 1st: Make a grid with four boxes. Place the alleles for
Parent 1 along the top of the grid using one letter for each
box. Place the alleles for Parent 2 along the left hand side
using one letter for each box.
 2nd: Fill in the grid. Combine the parent alleles inside the
boxes (capital letter always goes in the front).
 3rd: Fill in the offspring. Use the Law of Dominance to
determine the phenotype ratio of the offspring.
Monohybrid Cross
 Trait: Plant Height
 Alleles T- tall ; t –short
 Cross: Tt X Tt
 Genotypes: TT, Tt, tt
 Genotypic Ratio: 1:2:1
(TT=25% Tt = 50%, tt=25%)
 Phenotype: 3:1
(Tall = 75% Short = 25%)
Incomplete Dominance
 In incomplete dominance neither allele is not
completely dominant over another.
 In incomplete dominance, the heterozygous phenotype
is an intermediate (blended) phenotype between the
two homozygous phenotypes.
Codominance
 In codominance, an organism that has both alleles
of agene displays both phenotypes at the same time
(co-exists).
Multiple Alleles
 Multiple alleles are gene with more than two alleles.
 Many genes have multiple alleles, including genes for
blood type.
Mother
Father
Sex-linked Genes
 Sex-linked genes are located on the X chromosome.
 Traits determined by sex-linked genes are called sex-
linked traits.
 c= colorblind, C =normal)
 Ex .Color blindness
female Xc Xc
male Xc Y
 A carrier is a person that has the trait on only one
chromosome and does not express the trait. Carriers of
sex-linked traits are always women ( XC Xc).
Practice #3
 Eye color is a sex-linked trait in fruit flies. Complete
the chart below.
Character
Trait
Alleles
Eye Color
Red Eye
R
Eyes Color
White eye
r
Genotypes
Phenotypes
XRXR
XRXr
_______
___________
___________
White-eyed female
XRY
________
____________
White-eyed male
Answers
 Eye color is a sex-linked trait in fruit flies. Complete
the chart below.
Character
Trait
Alleles
Eye Color
Red Eye
R
Eyes Color
White eye
r
Genotypes
Phenotypes
XR XR
XR Xr
Xr Xr
Red-eyed female
Red-eyed female
White-eyed female
XR Y
Xr Y
Red-eyed male
White-eyed male
Karyotype
 A karyotype is a visual representation of an individual’s
chromosomes.
 A karyotype shows the complete diploid set of
chromosomes grouped together in pairs, which are
arranged in order of decreasing size.
Karyotype
Practice #4
 Is this a male or a female?
Answer
 It is a female because it has two X chromosomes for
the 23rd pair.
Pedigrees
 A pedigree is a diagram that traces the inheritance
of a particular trait through several generations.
 A pedigree uses symbols to illustrate the inheritance
of the trait.
Common Pedigree Symbols