Transcript Genetics

Section Outline
Section 11-1

11–1
A.
B.
C.
1.
2.
The Work of Gregor Mendel
Gregor Mendel’s Peas
Genes and Dominance
Segregation
The F1 Cross
Explaining the F1 Cross
Genetics
• This is the branch of biology which studies heredity.
White Tiger - This type of tiger can have yellow parents.
How can that happen?
Daschuand, Collie, Great Dane, Poodle, Greyhound,
Labrador, Terrier, Pit-bull
 What are some inherited traits for some dog breeds?
(Physical and behavior)
 How do you keep producing a pure breed?
 Terms -alleles, hybrid, genes, purebred, traits
11-1
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?
What is the F1 generation? What else did Mendel do?
This generation showed only one trait from the parents that were
crossed ( green pod, no yellow pod).
He allowed these to self-pollinate. This is called the F2
generation.
Results of this pollination showed 3/4 were green and only 1/4
were yellow. The yellow 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?
GREGOR MENDEL
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.
Mendel’s experiments:
1. He studied each characteristic individually. He took “pure” plants for a
trait and allowed them to go through self-pollination. What are pure
plants? What is self-pollination?
The offspring which resulted from this cross in known at the parental
generation or P1 generation. ( parent self-pollinated)
2. Mendel then crossed the P1 generation of opposite traits by crosspollinating them (yellow pods with green pods).
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 an 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)
 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
Go to
Section:
C.
Probability and Segregation
D.
Probabilities Predict Averages
Tt X Tt Cross
Section 11-2
Tt X Tt Cross
Section 11-2
Go to
Section:
Section 11-3
Interest Grabber
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
*Gene interactions(Recessive vs. Dominant) recessive genes
do not produce the enzyme for a trait to be demonstrated.
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)
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 xR’)
Polygenic Inheritance - traits are controlled by two or more
genes. (Ex Lab retrievers have two separate genes which
determine coat color)
Multiple alleles - numerous versions of a gene are possible.
(eye color, blood type, etc.)diagram
Section 11-3
Concept Map
Gregor
Mendel
concluded
that
experimente
d with
Pea
plants
“Factors”
determine
traits
Some alleles
are dominant,
and some alleles
are recessive
which is
called the
Law of
Dominance
Go to
Section:
Alleles are
separated during
gamete formation
which is
called the
Law of
Segregation
Figure 11-11 Incomplete
Dominance in Four O’Clock Flowers
Section 11-3
Go to
Section:
Figure 11-10 Independent
Assortment in Peas
Section
11-3
Go to
Section:
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.
*A human cell has about 100 000 different genes attached in a
single line on each chromosome.
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.
Punnett Square - name after Reginald Punnett who studied
genetics in the 1900’s.
Sutton - (1902) His Chromosome theory of heredity
states that genes are located on chromosomes and each
occupies a certain place. Each chromosome contains a form
of the gene called an allele.
There can be two or more alleles for each gene. (see
diagram)
Linked genes - they are found on the same chromosome
and do not undergo independent assortment. Discovered in
fruit flies by Thomas Hunt Morgan.
What if there was no crossing-over in any organism?
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.
Sex linkage - There is an exception to the rule that all
chromosomes has a matching homolog. This was
discovered by Nettie Stevens (1905) in her study of meal
worm chromosomes. The Y chrom is much smaller and a
different shape than the X chrom. Her promising scientific
career was cut short by cancer at age 41. (FYI)
Genes located on one of the sex chromosomes is said to
be sex linked.
How is the sex of offspring determined? (Review)
Crossing-Over
Go to
Section:
Crossing-Over
Go to
Section:
Crossing-Over
Go to
Section:
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