Download Father of Modern Genetics

General Biology
Unit Three
Genetics
Genetics – the study of heredity
Heredity – the passing of traits
from one generation to the next
Trait – a physical or physiological
characteristic coded for by a
gene
Gene – a portion of a
chromosome that codes for a
particular
protein
Allele
– a form
of a gene
Genetics
Gregor Mendel – “Father of
Modern Genetics”
Established three laws working
with peas – two are still used in
genetics
1st Law – the Law of Segregation
2nd Law – the Law of
Independent Assortment
Mom
(female)
Dad
(male)
Recessive
allele
Dominant
allele
Homologous
chromosomes
Genetics
Genotype – the set of genes an
organism has
Homozygous – alleles are the same
type
Heterozygous – alleles are
different
Genetics
Phenotype – the expression of
the genotype
Purebred – having a homozygous
genotype
Hybrid – having a heterozygous
genotype
D
D
d
D
d
d
D
D
d
Dd
Dd
d
Dd
Dd
Punnett Square
D
D
d
D
D
d
D
d
d
D
d d
Complete
Dominance
D
d
D
DD
Dd
d
Dd
dd
Monohybrid Cross
Genotypic Ratio – 1:2:1
Phenotypic Ratio – 3:1
Complete
Dominance
d
D
d
Dd
dd
Complete
Dominance
d
Dd
Monohybrid Cross
Genotypic Ratio – 2:2
Phenotypic Ratio – 2:2
dd
Dihybrid
Cross
B
B’
B
BB
BB’
B’
BB’
B’B’
Incomplete Dominance Cross
Genotypic Ratio – 1:2:1
Phenotypic Ratio – 1:2:1
A
O
B
AB
BO
O
AO
OO
Codominance
Genotypic Ratio – 1:1:1:1
Phenotypic Ratio – 1:1:1:1
Genetics
Autosomes – all chromosomes
except for the ones that
determine sex
Sex chromosomes – chromosomes
that determine sex
Sex linked traits – traits
controlled by genes on the sex
chromosomes
Human Sex
Chromosomes
♀
♂
X X
X Y
Human Sex
Chromosomes
♀
♂
XB
Xb
Xb
XBXb
XbXb
Y
XBY
XbY
Sex Linked Cross
Genetics
Sex limited traits – traits that
are found only in one sex
Sex influenced traits – traits that
are expressed differently in both
sexes
Mutations
A mutation is any change in the
DNA of an organism
Mutations occur due to:
- pathogen infection
- exposure to radiation
- introduction of chemicals
- nondisjunction
Mutations
Mutations involve:
- base pair substitutions
- base pair insertions or
deletions
- DNA segments
Mutations
Nondisjunction
Nondisjunction is the failure of
chromosomes to separate during
anaphase I of meiosis
The normal separation, disjunction,
produces daughter cells with 23
chromosomes each
Nondisjunction
Nondisjunction results in one
daughter cell with 24 chromosomes
and the other with 22 chromosomes
Nondisjunction
Monosomy is the result of the
fertilization of a normal gamete and
one that has only 22 chromosomes
Trisomy is the product of the
fertilization of a normal gamete and
one that has 24 chromosomes
Disjunction
Nondisjunction
Genetic Disorders
Remember:
Nondisjunction in gametes causes a change in
chromosome numbers that affects the development
of an embryo
Approximately 90% of nondisjunction events are
maternal in origin
Genetic Disorders
The presence of an extra chromosome (trisomy) or
lack of one (monosomy) accounts for approximately
50% of all spontaneous abortions
Genetic Disorders
Only three autosomal trisomies are survivable:
* trisomy 13 – Patau syndrome
* trisomy 18 – Edward syndrome
* trisomy 21 – Down syndrome
Genetic Disorders
Most fetuses with Patau or Edward syndrome will die
before birth
The few that are born are severely deformed and
usually die within their first year
Genetic Disorders
Karyotype of Down
syndrome (trisomy
21)
Genetic Disorders
Down syndrome is the most survivable of the
trisomies, but approximately 75% die before birth and
20% of those born will die before the age of ten
Genetic Disorders
Down syndrome effects:
* short stature
* a flat face with almond shaped
eyes
* enlarged protruding tongue
* broad hands with short fingers
* varying degrees of mental
retardation
Genetic Disorders
Of those that survive past the age of ten, life
expectancy has been extended to sixty years
However, after the age of forty many develop early
onset Alzheimer disease
Genetic Disorders
Nondisjunction also occurs with the sex
chromosomes:
* trisomy 23 – Klinefelter
syndrome (XXY)
* trisomy 23 – Triplo-X syndrome
(XXX)
* monosomy 23 – Turner
syndrome (XO)
Genetic Disorders
Triplo-X syndrome (XXX) results in a female
phenotype that is usually infertile and may exhibit
some intellectual impairment
Genetic Disorders
Klinefelter syndrome (XXY) results in a sterile male
phenotype that is of normal intelligence and upon the
onset of puberty exhibits unusually long arms, sparse
body hair, undeveloped testes and enlarged breasts
Genetic Disorders
Turner syndrome (XO) results in a sterile female
phenotype that fails to develop secondary sex
characteristics at puberty and is usually short in
stature
Approximately 97% of all (XO) fetuses die before
birth
DNA & RNA Structure
The monomers are nucleotides
Nitrogen base
Functions:
Heredity
Protein synthesis
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Phosphate group
Pentose sugar
DNA & RNA Structure
Examples:
•DNA
•RNA
Double
Single
stranded
stranded,
with three
double
helix
forms –
molecule
tRNA, rRNA,
and mRNA
DNA &
RNA
Structure
DNA & RNA Functions
DNA & RNA Base
Pairing
DNA & RNA Base Pairing
DNA replication
| | | | | | | | | | | | | | | | | |
A T G C A T T G A AG C T G G T A G
TACGTAACTTCGACCAT C
| | | | | | | | | | | | | | | | | |
RNA transcription
| | | | | | | | | | | | | | | | | |
AU G C A U U G A AG C U G G U A G
TACGTAACTTCGACCATC
| | | | | | | | | | | | | | | | | |
DNA Replication
Protein Synthesis
Protein synthesis goes on all the time in most cells
This very important process is directed by the
genetic code on DNA
Protein Synthesis
Protein synthesis occurs in two processes:
~ transcription (production of RNA
from DNA)
~ translation (production of
proteins from RNA)
Both processes are fueled by ATP
Protein Synthesis: Transcriptio
Protein Synthesis:
Transcription
RNA polymerase attaches to specific areas of the
DNA (genes) and “unzips” the hydrogen bonds
The RNA polymerase also begins the building of the
RNA by adding RNA nucleotides in accordance with
the DNA base sequence
Protein
Synthesis:
Transcriptio
n
Protein Synthesis: Transcriptio
Protein Synthesis:
Transcription
Once transcribed, mRNA and tRNA are sent out of
the nucleus and to the ribosomes in the cytoplasm
rRNA is transferred to the nucleolus to become a
part of newly formed ribosomes
Protein Synthesis: Translation
mRNA carries a series of codons that code for
specific amino acids
A codon is a sequence of three nucleotide bases on
mRNA
Since there are only four RNA bases and there are
three in each codon, there are 64 condon
possibilities
Protein Synthesis: Translation
The genetic code is the use of these 64 codons
coding for 20 amino acids
Remember - the synthesis of a specific protein
requires a specific sequence of amino acids
Protein Synthesis: Translation
Therefore the sequence of codons on mRNA must be
sequentially specific
The genetic code is commaless and non-overlapping,
meaning it is read in frames of three without gaps or
overlaps
Protein Synthesis: Translation
There is one initiation codon - AUG
There are three stop codons - UAA, UAG & UGA
Protein Synthesis - Translation
Translation is the process by which RNA produces
proteins in ribosomes
- mRNA carries the code from DNA
- tRNA carries amino acids to the
ribosome
- rRNA is a component of the
ribosome
Protein Synthesis: Translation
By way of the genetic code, RNA “translates” from
the language of nucleic acids to that of proteins
Protein
Synthesis:
Translation
Protein Synthesis: Review
Protein Synthesis: Review