Transcript Unit 6 - John Adams Academy

Unit 3
Based on the work of Gregor Mendel
 Genetics –

› the study of patterns of inheritance as
heredity characteristics (characters or traits)

Genes –
› particles of inheritance, segments of
chromosomal DNA
Began studying crosses involving only one
trait at a time
 Crossed a pure-breeding strain of red
flowered pea plants with a pure-breeding
strain of white flowered pea plants
 Produced hybrids –

› genetically mixed offspring, not purebred
› All were red

He then allowed all seeds to self-pollinate
› Produced ¾ all red & ¼ all white
Parental Generation
Red x White
(RR)
(rr)
First Filial Generation (F1)
All Red
(Rr)
Second Filial Generation (F2)
¾ Red
¼ White
II. Gene Pairs –
A. Alleles – different forms of a genetic trait (ex. red,
white)
B. Homozygous – having the same alleles
C. Heterozygous – having different alleles
III. Dominant and Recessive Alleles –
A. Dominant Allele – the allele that expresses itself
B. Recessive Allele – the allele that is masked or not
expressed
IV. Genotype and Phenotype –
A. Genotype – genetic make-up that cannot
determined merely by inspection
(Example – Rr)
B. Phenotype – the expression of its genes, visually
observed or chemically tested

A genetic cross in which only one trait of
the parents is of interest
P1
Red Flower
(RR)
P1 Gametes
F1
(one gene from
X
White Flower
(rr)
R
r
Rr
(Red Flowers)
each parent)
F2
(self-pollinated)
RR, Rr, Rr, rr

A genetic cross in which two different
pairs of contrasting alleles are of interest
Smooth Yellow Seed
P1
(SSYY)
P1 Gametes
Wrinkled Green Seeds
x
S,Y
F1
(ssyy)
s,y
SsYy
(Smooth Yellow Seeds)
F2 Gametes
SY,
Sy, sY,
sy
(gene pair combinations for F2)
F2 SY
Sy
sY
sy
SY
SSYY
SSYy
SsYY
SsYy
Sy
SSYy
SSyy
SsYy
Ssyy
SsYY
SsYy
ssYY
ssYy
SsYy
Ssyy
ssYy
ssyy
sY
sy
Genotype Ratios –
SSYY – 1/16
SSYy – 2/16
SsYY – 2/16
SsYy – 4/16
SSyy – 1/16
Ssyy – 2/16
ssYY – 1/16
ssYy – 2/16
ssyy – 1/16
Phenotype Ratios –
Smooth/YellowSmooth/GreenWrinkled/YellowWrinkled/Green -
9/16
3/16
3/16
1/16
Occurs when two alleles combine their
effects – neither is recessive
 The heterozygote has a different
phenotype, as well as a different
genotype, from either homozygote
 Codominance –

› Occurs when each allele is expressed
separately –
› Example: black and white feathers
R= red flower
R1 = White flower
(not r because it is not recessive)
P1
P1 Gametes
RR
x
R
R1
F1 Pink
Flowered
F2
Genotype Ratio
Phenotype Ratio
R1R1
RR1
RR
1 RR
1 red
RR1
RR1
2 RR1
2 pink
R1R1
1 R1R1
1 white
Humans contain 23 pairs of chromosome
 Each single chromosome contains many
to hundreds of genes

A.
Mutation –
1. A rare, unpredictable and inheritable
change in a cell’s genetic material
2. Becomes a part of the genotype of the cell
and of all its descendants
3. Most mutations produce recessive alleles
B.
Lethal Alleles:
- Most will die prematurely because their
DNA lacks a certain protein
1.
Brachdactyly in humans (shortening of the middle fingers)
Parents
BB1
BB1
Offspring
BB
BB1
BB1
B1B1
**Homozygous babies lack fingers and
show other skeletal defects that cause
death in infancy. **
2.
3.
Manx cat (no tail)
Sickle Cell Anemia - shows co-dominance with normal
alleles
- If heterozygous = HbAHbS (carrier)
- If homozygous = HbSHbS
(affected individual)
- 50% die by age 20
4.
Tay-Sachs - metabolic disorder resulting in
deterioration of the brain
- death by 5
- 1/30 East European Jewish persons
are carriers
5.
Cystic Fibrosis - 1/20 Caucasians is a carrier
- death the age of 20
- high concentration of sodium, potassium
& chloride in sweat
- production of thick mucous, clogging the
respiratory passages
A.
Mammals –
Parents
Female XX
Gametes
Offspring
B.
X
Male XY
X or Y
XX
XY
Birds, moths, butterflies & amphibians
are opposite – female(ZW) & male(ZZ)
c. Sex Chromosomes One sex is heterozygous, one homozygous
for the entire pair of chromosomes
2. The possession of a particular sex
chromosome causes an embryo to
develop into a male or a female = process
of sex differentiation
3. Most genes involved in the production of
male and female characteristics, sex
hormones, are located on autosomes - not
sex chromosomes!
4. All individuals have the genes needed to
develop into a member of either sex –
hormonal treatment- birds, fish
1.
5.
Sometimes, sex chromosomes fail to
segregate normally during meiosis,
resulting in individuals with abnormal
numbers of sex chromosomes.
a. XXX = female, fertile or sterile, usually normal
b. X = Turner’s syndrome; female, sterile,
ovaries are rudimentary or absent
c. XXY = Klinefelter’s syndrome; male sterile,
possible mental retardation
d. XXXY = male
e. XYY = male, tall, acne-prone, impaired
fertility
A.
B.
C.
D.
E.
F.
Sex chromosome carry genes
Mammalian X chromosomes have large nonhomologous portions (no mates of the Y) = sex
linked
In males, any recessive allele on a nonhomologous parts of the X chromosome will
be expressed in the phenotype
Females must have two copies of the
recessive allele for a phenotype
Since many recessive alleles are bad more
males have these disorders
Examples: Red-green colorblindness,
hemophilia, one type of muscular dystrophy,
SCID
A.
B.
Genes that are expressed to a greater
or lesser degree as a result of the level
of sex hormones
Examples: baldness, gout
(Affects males mostly, high uric acid in
the blood which allows crystals to form
which are deposited into the
connective tissues which causes pain.
This disorder can lead to arthritis).
A.
B.
C.
D.
Long, Twisted, double stranded helix
consisting of a chain of nucleotides.
Nucleotides consist of a sugar, a
phosphate & a nitrogen base
The four base pairs include – adenine,
cytosine, guanine & thymine
Strands are “complimentary” – they can
only pair one other base pair –
Adenine – Thymine & Cytosine - Guanine
Copyright Pearson Prentice Hall

A.
DNA directs the synthesis of proteins
using RNA (ribonucleic acid)
Three types of RNA –
1. rRNA – makes up the ribosome of the cell
2. mRNA – carries the DNA message from the
nucleus to the ribosome for protein synthesis
3. tRNA – carries amino acids to the ribosome
B.
Transcription –
›
›
›
When DNA instructions are copied into RNA
RNA is synthesized on one of the two strands
of DNA
Not an exact copy due to the replacement
of Uracil for Thymine (A,U,C,G)
Translation –
C.
›
›
Process by which the cells convert the
genetic message from the mRNA into
proteins
mRNA is translated by the ribosome resulting
in a chain of amino acids called proteins.





As tRNA moves the amino acids together,
long chains are formed (proteins)
There are 20 different amino acids
The structure and function of the protein
depends upon the amino acids present
and the order in which they are attached
The base pairs (A, U, C, G) are arranged in
codons or words of 3
Each codon stands for one amino acid
XV. Factors that affect gene expression 1. Age
2. Diet
3. Light
4. Temperature
XVI. Genetic Counseling –
1. Blood tests
2. Amniocentesis –
- detects abnormal chromosomal numbers
in the fetus during the 16th week of
pregnancy
A.
Recombinant DNA –
›
›
›
›
Produced from recombining DNA from
different organisms
Allowed because the genetic code is
mostly universal among all organisms
Using enzymes, scientists cut DNA sections
and paste them into bacterial cell plasmids,
which then replicate them quickly.
Examples –
 Insulin Production
 Cancer and AIDS research
 Cattle Production
XVIII. Scientists Important to Genetics 







Gregor Mendel
Charles Darwin –
› Father of Evolution/Natural Selection
Watson & Crick › Discovered the shape of DNA
Beadle & Tatum –
› Worked with Gene Mutations
Hershey & Chase –
› Determined that genes are on chromosomes, not proteins
Thomas Morgan – worked with mutant Fruit Flies
Mary Lyon – Studied Barr bodies (inactive X chromosome)
Tsui & Riordan – cloned Cystic Fibrosis Gene