Transcript Genetics

Section Outline
•
11–1 The Work of Gregor Mendel
A. Gregor Mendel’s Peas
B. Genes and Dominance
C. Segregation
1. The F1 Cross
2. Explaining the F1 Cross
Gregor Mendel history
Bill Nye
11-1 Quiz?
1. Discuss who Gregor Mendel was and discuss his
contribution to biology.
2. What characteristics did he study?
3. What is the P1, F1, F2 generation?
4. What are pure plants? Give one example of self-pollination and
cross pollination.
5. How did Mendel determine which of each pair of traits was the
dominant trait and which was recessive?
6. Although Tall plants appear to be tall, could they be considered
“pure” for the tall trait? Why or why not?
GREGOR MENDEL prezi
Mendel was a monk who lived
during the mid 1800’s in
Austria. He was great in math
and was a gardener at the
monastery. He noticed
various things about pea
plants and their
characteristics.
He studied seven characteristics of
pea plants and noticed what
we today call inheritance or
the passing of traits by
heredity.
P1- pure parent cross contrasting traits
F1 generation
This generation showed only one trait from the parents
showed up. (dominant)
Mendel allowed these to self-pollinate. This is called the F2
generation.
Results of this pollination showed 3/4 were yellow and only
1/4 were green. The green pod trait had appeared to be
lost in the F1 generation, actually reappeared in the F2
generation.
• How did Mendel determine which of each pair of traits was
the dominant trait and which was recessive?
• Although Tall plants appear to be tall, could they be
considered “pure” for the tall trait? Why or why not?
Principles of Dominance
Section 11-1
P Generation
Tall
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Figure 11-3 Mendel’s Seven F1
Crosses on Pea Plants
Section 11-1
Seed Coat
Color
Pod
Shape
Pod
Color
Flower
Position
Smooth
Green
Axial
Tall
Yellow
Terminal
Short
Green
Axial
Seed
Shape
Seed
Color
Round
Yellow
Gray
Wrinkled
Green
White
Constricted
Round
Yellow
Gray
Smooth
Plant
Height
Tall
Conclusions of Mendel
1. Principle of dominance and Recessiveness
One factor of a pair of alleles may mask the appearance of another.
(Ex: blond hair is recessive to dark hair)
2. Principle of Segregation The two factors for a characteristic separate,
during the formation of eggs and sperm.
(B - Brown, b - blue) Which allele did you get?
3. Principle of Independent Assortment- Factors for different
characteristics are distributed independently to sex cells.
(curly fur /size of dog or tall plant /wrinkled seeds)
These principles will make more sense at the end of the chapter.
• Mendel’s most important decision was to study just a few isolated
traits of the pea plants.
Section 11-1
Parents
First Generation
Second Generation
Long stems  short stems
All long
787 long: 277 short
Red flowers  white flowers All red
705 red: 224 white
Green pods  yellow pods
All green
428 green: 152 yellow
Round seeds  wrinkled seeds
All round
5474 round: 1850 wrinkled
Yellow seeds  green seeds All yellow
6022 yellow: 2001 green
What do the numbers mean?
What is the ratio of dominant
to recessive?
Section Outline
Section 11-2
•
11–2 Probability and Punnett Squares
A. Genetics and Probability
B. Punnett Squares
C. Probability and Segregation
D. Probabilities Predict Averages
Go to
Section:
Punnett squares
1-factor
Punnett squares
2-factor
Tt X Tt Cross
Section 11-2
Tt X Tt Cross
Section 11-2
Go to
Section:
Figure 11-10 Independent
Assortment in Peas
Section
11-3
Go to
Section:
Section 11-3
Height in Humans
• Height in pea plants is controlled by one of two
alleles; the allele for a tall plant is the dominant
allele, while the allele for a short plant is the
recessive one.
• What about people?
• Are the factors that determine height more
complicated in humans?
• Can you only be tall or short?
Go to
Section:

11–3 Exploring Mendelian Genetics
A. Independent Assortment
1. The Two-Factor Cross: F1
2. The Two-Factor Cross: F2
B. A Summary of Mendel’s Principles
C. Beyond Dominant and Recessive Alleles
1. Incomplete Dominance
2. Codominance
3. Multiple Alleles
4. Polygenic Traits
D. Applying Mendel’s Principles
Polygenic Inheritance - traits are controlled by two or more genes. (Ex
Lab retrievers have two separate genes which determine coat color)
Human skin color link
Multiple alleles - numerous versions of a gene are possible.
(Hair color, eye color, blood type, etc.) eye link
Codominance - both differing alleles of a gene are expressed at the same time. There
is no dominance of one over the other. (Ex: roan cattle are a hybrid of a Red and
White cross R x R1)
Charlais
(R1 R1)
Red
(RR)
X
Roan hybrid
(R R1 )
Incomplete dominance - hybrids are intermediates of the
parents.
(Ex red x white = pink). The recessive allele can not
make any pigment at all so less pigment shows up
(diagram)
Go to
Section:
Section 11-3
Concept Map
Gregor
Mendel
concluded
that
experimented
with
Pea
plants
Different traits
separate
randomly
“Factors”
determine
traits
Some alleles
are dominant,
and some alleles
are recessive
which is
called the
Law of
Dominance
Go to
Section:
which is
called the
Law of
Independent
assortment
Alleles are
separated during
gamete formation
which is
called the
Law of
Segregation
Section 11-4
Interest Grabber continued
1. How many chromosomes would a sperm or an egg contain
if either one resulted from the process of mitosis?
2. If a sperm containing 46 chromosomes fused with an egg
containing 46 chromosomes, how many chromosomes
would the resulting fertilized egg contain? Do you think this
would create any problems in the developing embryo?
3. In order to produce a fertilized egg with the appropriate
number of chromosomes (46), how many chromosomes
should each sperm and egg have?
Go to
Section:
Section Outline
11–4
Meiosis Prezi link Use instead
A. Chromosome Number
B. Phases of Meiosis
1.Meiosis I
2.Meiosis II
C. Gamete Formation
D. Comparing Mitosis and Meiosis
Meiosis
• This is the division of chromosomes that creates new cells
with half the number of chromosomes (haploid)
• This type of cell division occurs in sex cells egg, sperm,
pollen, spores,etc.
• They have the chromosome number of 1n
• (1n + 1n = 2n) (Diploid)
• Two main parts of Meiosis:
Meiosis I - Homologous Chromosomes separate into
separate cells
Meiosis II - Chromatids of each chromosome are segregated
into separate cells.
Figure 11-15 Meiosis
Meiosis I
Section 11-4
Interphase I
Prophase I
Metaphase I
Cells undergo a round
of DNA replication,
forming duplicate
Chromosomes.
Each chromosome pairs
with its corresponding
homologous chromosome
to form a tetrad.
Spindle fibers attach to the The fibers pull the
homologous chromosomes
chromosomes.
toward the opposite ends of
the cell.
Go to
Section:
Anaphase I
Figure 11-17 Meiosis II
Section 11-4
Prophase II
Meiosis II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up
The sister chromatids
haploid (N) daughter cells, in a similar way to the
separate and move toward
each with half the number metaphase stage of mitosis. opposite ends of the cell.
of chromosomes as the
original.
Go to
Section:
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Meiosis I
Prophase I
DNA replication has already happened.
Metaphase I
 DNA condenses
into
 Tetrads
chromosomes.
(Homologue)
 Nuclear
move to the
membrane
middle of the
disappears
 Each
cell
chromosome
lines up next to
its homologue
 These
homologues twist
around each
other to form a
tetrad and
genetic material
can be
exchanged
(crossing- over)
Anaphase I
Telophase I
 The cytoplasm
 The
divides,
Homologous
forming two
pairs of
new daughter
chromosomes
cells. Each
separate.
cell has one of
 One
the
chromosome
homologues.
of each hom.
Pair moves to
each side.
 The sister
chromotids
did not
separate.
Meiosis II No DNA replication has happened.
Prophase II Metaphase II
Anaphase II Telophase
 Recoiling may  Chromosomes  Centromeres
are moved to
occur to form
joining the
the middle of
chromosomes
chromatids
the cell
from
divide
chromatin
 Sister
 Spindles form
chromatids
are now
separate
 Each
chromatid is
moved to the
opposite pole
 Spindles
disappear
 Nuclear
membrane
forms
 Chromatids
unwind into
chromatin
 Cytokinesis
occurs
separate from
meiosis
Egg and Sperm Formation
Gametes - sex cells that have half the number of
chromosomes as somatic cells (body) p. 278
• Sperm are formed in the male sex organs
through the process of meiosis. Four (4) new
sperm are produced from this process from
every “mother cell”.
• Eggs are formed in the female sex organs
through meiosis. One egg cell or ootid and three
(3) polar bodies are produced from every
“mother cell”.
Genetic Variation
Sexual reproduction - fusion of gametes with different genetic
material. Offspring are genetically different than parents.
Asexual reproduction - there is no exchange of genetic material.
Organism is identical to parent. Binary fission, budding,
cloning.
How does genetic variety help organisms survive?
(Think of long-term populations, not individuals)
Section
11-4
Crossing-Over
of tetrads
FYI
Reduction Division reduces the number of chromosomes per daughter cell by half.
Prophase I – can last years. Human females have potential eggs which have entered prophase I
by birth. Eggs remain “stuck” in this stage for decades.
Oocytes – germ cells with potential to form eggs are in follicles, found in the ovary tissue. Each
follicle has a single oocyte. All germ cells are in prophase I of meiosis by birth. Oocyte grows
and is packed full of nutrients for a developing embryo. Oogensis – egg forms and follicle
ruptures releases the egg. Ovulation occurs. Meiosis II is completed after the fertilization of
the
1 egg. 3 polar bodies are produced and disintegrate.
Synapsis – process of chromosome alignment in Prophase I. Synapsed pair of homologous
chromosomes are called a tetrad. Crossing over can occur.
Sperm – produced in seminiferous tubules from stages of cells.
Spermatogonia primary spermatocytes spermatidsimmature sperm
Janssens (1909) predicted crossing over leads to genetic
recombination/ which increases diversity of all life.
Chiasmata- the points where two homologous chromosomes are in contact. Site
where crossing over takes place. Crossing over does not require the breakage an
reunion of thick, compact chromosome pieces, but of individual DNA molecules
(nucleotides+nucleotides).
There are 223 combination possible in humans for to independent assort (8million
possibilities)
1 in 70 million chance of having identical siblings in different pregnancies.
Pleiotrophy – product of one gene can cause many problems.
(Ex: cystic fibrosis)
Epistasis – one pair of alleles (recessive) effect the genes or alleles at another loc
(part of chromosome). Ex: Albinism
Section Outline
Section 11-5
•
11–5 Linkage and Gene Maps
A. Gene Linkage
B. Gene Maps
Go to
Section:
What are some products that often come in packages containing
several different colors and flavors?
What happens if you want only one flavor? What else do you get
besides the color or flavor you want?
Linkage groups- these are “packages” of genes that tend to be
inherited together. There is one linkage groups for every homologous
pair of chromosomes.
*Crossing Over
If genes for body color and wing size are linked, why aren’t they
linked all the time? Sections of the chromosomes can cross, break
and reattach during Meiosis I. (see diagram)
Recombinants - individuals with new combinations of genes. It is
believed that 2-3 cross-overs occurs on each pair of human homologs
in sex cells.
Linked genes - they are found on the same chromosome and do not
undergo independent assortment. Discovered in fruit flies by Thomas
Hunt Morgan.
Chromosomes assort, not individual genes.
http://www.biologycorner.com/fruitflygenetics/index.html
Why are fruit flies used in genetics?
Gene Mapping
Distance between genes (alleles) determines how often crossing over
occurs. The farther apart- the more likely genes are to cross-over. This
distance helps to “map” a chromosome and tell the probable place to
find a certain gene on the chromosome.
Genes located on one of the sex chromosomes is said to be sex linked.
Crossing-Over
Go to
Section:
Crossing-Over
Go to
Section:
Crossing-Over
Go to
Section:
5% recombination
1% recombination
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9
17
Figure 11-19 Gene Map
of the Fruit Fly
Section 11-5
Exact location on chromosomes
Go to
Section:
Chromosome 2
Comparative Scale of a Gene Map
Section 11-5
Mapping of Earth’s
Features
Mapping of Cells,
Chromosomes, and Genes
Cell
Earth
Country
Chromosome
State
Chromosome
fragment
City
People
Go to
Section:
Gene
Nucleotide
base pairs