Transcript Tall - TeacherWeb

Introduction to
Genetics
Genetic variation within the
White-cheeked Rosella
Heredity & Genetics
1. Heredity: The passing of
traits from parents to
offspring
2. Genetics: Study of heredity
3. Inherited characteristics
are called traits
Gregor Mendel was the first person to
predict how traits are transferred.
Austrian monk who
studied garden peas
Mendel used peas because
-they Reproduce sexually
- gametes in the same
flower
- Fertilization could be
controlled
http://www2.edc.org/weblabs/WebLabD
irectory1.html
-Mendel transferred pollen from
plant to plant and then studied
resulting peas
-Studied only one trait at a time
- Mendel is called the “father of
genetics”
Figure 11-3 Mendel’s Seven F1
Crosses on Pea Plants
Section 11-1
Go to
Section:
Seed Coat
Color
Pod
Shape
Pod
Color
Smooth
Green
Seed
Shape
Seed
Color
Round
Yellow
Gray
Wrinkled
Green
White
Constricted
Round
Yellow
Gray
Smooth
Flower
Position
Plant
Height
Axial
Tall
Yellow
Terminal
Short
Green
Axial
Tall
Phenotypes & Genotypes
Phenotype: appearance of an organism
Example: short, tall, green, yellow
Genotype: gene combination of an
organism
Example: tt, TT, Tt, gg, GG, Gg
Heterozygous & Homozygous
Heterozygous: the 2 alleles are
different
Example: Tt -heterozygous
Homozygous: the 2 alleles are the same
Example: TT means homozygous
dominant, and tt means homozygous
recessive
Livestock: http://www.parkelivestock.com/semensales.htm
http://www.mcrobertsgamefarm.com/buffalo/white_buffalo.htm
Traits can be dominant or recessive
Dominant traits: exhibited trait,
written with 1 or 2 capital letters
Example: T
Recessive traits: inhibited trait,
written with recessive
letters(lowercase letters)
Example: t
Monohybrid Crosses
Crosses that differ by a single trait
Example: Tall pea plant x short pea plant
The first generation produced offspring
resembling only one parent
Example: all tall pea plants
Principles of Dominance
Section 11-1
P Generation
Tall
Go to
Section:
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Principles of Dominance
Section 11-1
P Generation
Tall
Go to
Section:
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
The second generation produced:
3/4 of peas were tall
1/4 of peas were short
Mendel concluded that each trait
has 2 factors
Factors are now called alleles
Inherit one allele from
mother and one allele from
father
Principles of Dominance
Section 11-1
P Generation
Tall
Go to
Section:
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Tt X Tt Cross
Section 11-2
Go to
Section:
Tt X Tt Cross
Section 11-2
Go to
Section:
Probability: the chance or percentage
of chance of a trait being exhibited
Mendel Revisited
• Quick Review
– Genotype: genetic code for traits TT Tt tt
– Phenotype: physical appearance
– Homozygous, heterozygous, dominant, recessive
• Punnett Square:
– TT x tt
– Tt x Tt
Mendel’s Laws
• Law of Dominance
– In a cross of parents that are pure for contrasting traits,
only one form of the trait will appear in the next generation.
Offspring that are hybrid for a trait will have only the
dominant trait in the phenotype.
TT (tall) x tt (short)
all Tall
• Law of Segregation
– During the formation of gametes (eggs or sperm), the two
alleles responsible for a trait separate from each other.
Alleles for a trait are then "recombined" at fertilization,
producing the genotype for the traits of the offspring.
Tt (tall) x Tt (tall)
alleles act independently
75% Tall 25% short
Incomplete dominance
Incomplete dominance
-neither allele is
Dominant or recessive
Example- white
flowers X red flowers=
pink flowers
-a mixture or blend of
the parent colors
Codominance
offspring shows
phenotype of neither
parent both alleles are
dominant
Example- bay horse x
white horsed= roan horse
- both hair colors are
present
Multiple and Sex-linked Alleles
Multiple alleles: more than 2 alleles
control a trait
Example-blood type in humans
a. blood type is determined by
presence or absence of
proteins on the surface of
red blood cells
Examples- A, B, AB, & O
Genotype
AA, Ao
Phenotype
A blood
BB, Bo
B blood
OO
O blood
To determine the blood types of
possible offspring
Parents = A blood, O blood
Genotypes AA, AO
OO
Calico Cats
• Calico is not a breed of cat, but an unusual
coloring occurring across many breeds
• Virtually all calico cats are female
– a male calico is a genetic anomaly and usually
sterile
– Producing calico kittens through selective breeding
also is nearly impossible due to unpredictable
actions of genes and chromosomes when cells
multiply in a feline fetus
Sex linked alleles: controlled by genes
located on sex chromosomes
-usually carried on the X
chromosomes
-Females XX, males XY
-If trait is X-linked, males pass
the trait on to all their daughters,
but none to their sons
-mothers have 50/50 chance of
passing it to all their children
Examples-colorblindness
Colorblindness,Hemophilia, MD
• Colorblindness – recessive disorder where a
person can’t distinguish between certain
colors.
• Hemophilia – blood clotting disorder
• Muscular Dystrophy – deterioration of the
skeletal muscle. Children rarely live past
early adulthood.
Colorblindness test
• http://www.geocities.com/Heartland/8833/c
oloreye.html
Aneuploidy
• Abnormal # of chromosomes
• Trisomy – aneuploidy of the 1st 22 pairs of
chromosomes
– Autosomes – 1st 22 pairs of chromosomes.
• Turners Syndrome – XO 1/2000. Females that
lack ovaries, shorter, and live normal lives.
• Klienfelters syndrome – 1/500 males XXY taller
than avg., longer limbs, sterile
Karyotype
• A chart of all 23 pairs of chromosomes
– Tell the sex of the child
– Aneuploidy yes/no
Significance of cell reproduction
Unicellular
Organisms: reproduce
by cell division, this is
also called binary
fission.
Multicellular organisms- growth and
repair upon cell division, also the
production of sex cells.
Chromosomes
-Carriers of
genetic material
found in nucleus
-Made up of
DNA
-Information is
copied and
passed to
future
generations
Usually exist as chromatin
-long, winding strands
which condense into
chromosomes before
dividing
Humans have 46 chromosomes in body
cells, 23 in sex cells
Meiosis
•
•
•
•
Similar in many ways to mitosis
Several differences
Involves 2 cell divisions
Results in 4 cells with 1/2 the normal genetic
information
Vocabulary
• Diploid (2N) - Normal amount
of genetic material
• Haploid (N) - 1/2 the genetic
material.
• Meiosis results in the formation
of haploid cells.
• In Humans, these are the Ova
(egg) and sperm.
• Ova are produced in the ovaries
in females
• Process is called oogenesis
• Sperm are produced in the
testes of males.
• Process is called
spermatogenesis
Meiosis Phases
• Meiosis occurs in 2
phases; Meiosis I, &
Meiosis II.
• Meiosis I.
– Prior to division,
amount of DNA
doubles
Crossing Over
• During metaphase 1
homologous
chromosomes line-up
along the metaphase
plate
• Areas of homologous
chromosomes connect
at areas called
chiasmata
Crossing over contd.
• Crossing Over of genes
occurs now
– Segments of homologous
chromosomes break and
reform at similar locations.
– Results in new genetic
combinations of offspring.
– This is the main
advantage of sexual
reproduction
Chromosome reduction
• During anaphase 1,
each homologous
chromosome is
pulled to opposite
sides of the cell.
Unlike mitosis,
THE
CENTROMERES
DO NOT BREAK.
Meiosis I continued
• Nuclei may or
may not reform
following
division.
• Cytokenesis may
or may not occur
Meiosis II
• DNA does not double
• Chromosomes randomly
line-up along metaphase
plate like regular mitosis.
• During anaphase 2,
CENTROMERES
BREAK and each
chromosome is pulled to
opposite sides of the cell.
• Nuclei reform and
cytokenesis usually occurs
(although it is often
unequal).
Overview of Meiosis
Comparison of Mitosis & Meiosis