Transcript Ch 10: Mendel and Meiosis

Ch 10: Mendel and Meiosis
Section 10.1 - Mendel’s Law
of Heredity
Section 10.1
Inside This Section...
Who is Gregor Mendel
Mendel’s Crosses
Phenotypes and Genotypes
Probability in Genetics
Section 10.1
Who is Gregor Mendel?
Known as the father of modern genetics
Developed the principles of heredity by
studying the variation and heredity of
seven pairs of inherited characteristics
in pea plants.
The significance of his work was not
recognized during his lifetime.
Section 10.1
Genetics
Genetics is the branch of biology that studies heredity
Heredity is the passing of characteristics from parents to offspring
Traits are inherited characteristics
Section 10.1
More Definitions
Gametes are the sex cells that allow
an organism to reproduce
A hybrid is the offspring of parents
who have different traits
Section 10.1
Reproduction in Peas
Both male and female parts on
the same flower
Male gamete is in the pollen grain
Female gamete is in the ovule
(located in the pistil)
Section 10.1
Reproduction in Peas
Pollination is the transfer of male
pollen grains to the pistil
Fertilization happens when the
male and female gametes unite
Section 10.1
The Generations
Parental (P) Generation
F1 Generation
F2 Generation
The Rule of Factors
Each organism has two factors that control each trait
These factors are called genes and are found on the
chromosomes and have alternate forms
The different gene forms that control one trait are called
alleles
Section 10.1
Alleles and Genes
Section 10.1
The Rule of Dominance
Dominant: The trait that is more
expressive in alleles than other traits
(represented by a capital letter)
Recessive: The trait that is submissive in
the alleles to the other traits. (Represented
by a lowercase letter)
If an organism contains a dominant and a
recessive allele, the dominant trait will be
expressed
TT or Tt
tt
Section 10.1
The Rule of Dominance
Phenotype is the physical expression
of an organism genes
Genotype is the genetic makeup of an
organism
TT or Tt
tt
Section 10.1
The Law of Segregation
Alleles separate during
meiosis
Each new cell gets one allele
for each gene
TT or Tt
tt
Section 10.1
The Law of Independent assortment
•
All traits are inherited independently from each other
Section 10.1
Two types of Crosses
Monohybrid Cross: A cross in which ALL traits are
identical except one
Dihybrid Cross: A cross in which two traits differ between
organisms
Section 10.1
Mendel’s Monohybrid Cross
When Mendel crossed tall pea
plants with short ones, the first
generation (F1) consisted of all
tall plants
When he crossed the F1
generation, 3/4 of the F2
generation were tall and 1/4 were
short
F2 F1- 3 Generation
tall
All :Tall
1 short
P: Parental
Section 10.1
The Punnett Square
Named after Reginald
T
PunnettUseful for making offspring
PredictionsAlleles for 1 parent
placed at the top and for the other
at the leftEach box is filled with the
allele to the top and to the left
T
t
t
Mendel’s Dihybrid Cross
When Mendel crossed Round Yellow peas with wrinkled green
peas, all of the F1 generation were Round Yellow PeasIn the F2
generation, the following ratios were found:9 Round Yellow3
Round Green3 Wrinkled Yellow1 Wrinkled Green
Section 10.1
Mendel’s Dihybrid Cross
RrYy * RrYy
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
Probability & Genetics
Section 10.1
In Review...
Who is Gregor Mendel
Mendel’s Crosses
Phenotypes and Genotypes
Probability in Genetics
Ch 9: Energy in a Cell
Section 10.2 - Meiosis
Section 10.2
Inside This Section...
The Two Types of Cells
Chromosomes and Genes
What is Meiosis?
Genetic Recombination
Section 10.2
Two Types of Cells
Diploid: A cell with two of
each kind of
Chromosomes (both
alleles for each gene)
We signify this by writing
2n
All cells in the body
except sex cells are
diploid
Haploid: A cell with one of
each kind of Chromosome
(only one allele for each
gene)We signify this by
writing an ”n”Sex cells
are Haploid
Section 10.2
Chromosomes and Genes
Chromosomes usually have about a
thousand or more genes
Chromosomes occur in pairs
Each chromosome has one allele for a
particular gene
Each species contains a characteristic
number of chromosomes
Section 10.2
Number of Chromosomes
Chromosome Numbers of Some Common Organisms
Organism
Body Cell (2n)
Gamete (n)
Fruit fly
8
4
Garden pea
14
7
Corn
20
10
Tomato
24
12
Leopard frog
26
13
Apple
34
17
Human
46
23
Chimpanzee
48
24
Dog
78
39
2360
630
Adder’s tongue fern
Section 10.2
What is Meiosis?
A Process of cell division that results in the
production of sex cells (gametes)
Consists of
Interphase: Cell replicates chromosomes
Meiosis I: Results in 2 haploid cells
Meiosis II (similar to mitosis): Results in 4 haploid
cells
Section 10.2
Meiosis
Section 10.2
Meiosis I
Prophase I
Homologous chromosomes come together and
form a tetrad (four-part structure)
Sometimes chromosomes exchange genetic
material in a process called crossing over
Section 10.2
Section 10.2
Crossing Over
Section 10.2
Meiosis I
Metaphase I
Spindle fibers cause Homologous Chromosomes to
line up side by side at the equator
Section 10.2
Section 10.2
Meiosis I
Anaphase I
Homologous chromosomes separate making each
new cell haploid
Section 10.2
Section 10.2
Meiosis I
Telophase I
Reversal of Prophase I
Spindle breaks down, chromosomes uncoil,
cytoplasm divides
Section 10.2
Section 10.2
Meiosis II
Identical to Mitosis
Results in 4 Haploid cells
Section 10.2
Section 10.2
Genetic Recombination
Genetic recombination is the source of variation. This is caused by the
re-assortment or crossing over during meiosis
7 pairs of chromosomes = 27 = 128 combinations
Any egg can be fertilized by any sperm, so 128 x 128 = 16,384
possibilities
N=23, 223 = 8,388,608 possibilities
8,388,608 x 8,388,608 = 7 Trillion possibilities
Crossing over is the exchange of genetic material during prophase I,
which results in new combinations of Alleles
Section 10.2
In Review...
The Two Types of Cells
Chromosomes and Genes
What is Meiosis?
Genetic Recombination
Ch 9: Energy in a Cell
Section 10-3: Mistakes in
meiosis
Section 10.3
Inside This Section...
Nondisjunction
Triploidy and Polyploidy
Section 10.3
Nondisjunction
When chromosomes fail to
separate during meiosis.
Trisomy: When one gamete gets
an extra chromosome, causing the
other gamete to be short by one
(e.g. Down’s syndrome - trisomy
21)
Monosomy: When one gamete
lacks one chromosome
Section 10.3
Triploidy and Polyploidy
Triploid is a total lack of separation of
homologous chromosomes.
Polyploids are organisms that have more
than the normal amount of chromosomes
Rare in animals usually causing death
Frequently occurs in plants causing fruit and
flowers to be larger
Section 10.3
In Review...
NondisjunctionTriploidy and Polyploidy