Transcript Monohybrid Crosses & Phenotypes and Genotypes

Mitosis VS Meiosis
Significance of cell reproduction
Unicellular
Organisms:
reproduce by a
type of cell
division 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
• However there are several differences
– Involves 2 cell divisions (mitosis only has
one)
– Results in 4 cells with 1/2 the normal genetic
information that are not identical (mitosis
results in 2 cells)
• 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
Vocabulary
Comparison of Mitosis & Meiosis
Page 276
Meiosis Phases
• There are 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
CENTROMER
ES DO NOT
BREAK.
Meiosis I continued
• Nuclei may or
may not reform
following
division.
• Cytokenesis
may or may not
occur
• 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).
Meiosis II
Overview of Meiosis
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 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”
Mendel used pea plants because
- they reproduce sexually
- have both male and female
gametes in the same flower
- fertilization could be
controlled
http://www2.edc.org/weblabs/WebLabD
irectory1.html
Figure 11-3 Mendel’s Seven F1
Crosses on Pea Plants
Section 11-1
Seed
Shape
Round
Wrinkled
Round
Go to
Section:
Seed Coat
Color
Seed
Color
Yellow
Green
Yellow
Gray
Pod
Shape
Pod
Color
Smooth
Green
White
Constricted
Gray
Smooth
Yellow
Green
Flower
Position
Plant
Height
Axial
Tall
Terminal
Short
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: TT, Tt
Recessive traits: inhibited trait
(not expressed unless homozygous),
written with lowercase letters
Example: tt
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:
F1 Generation
Short
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
- Organisms 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
Now you know that the probability of a
heads-up landing when you flip a coin is
1/2.
What is the probability of getting tails
if you flip it again?
- It is still 1/2.
The two events do not affect each
other. They are independent!
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
• 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 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.geociti
es.com/Heartland/
8833/coloreye.ht
ml
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
Pedigree Analysis