Download 11-1 - Cloudfront.net

Chapter 11: Introduction to
Genetics
California content standards: Genetics 2c, d, g; 3a, b
2c. Students know how random
chromosome segregation explains the
probability that a particular allele will be in
a gamete.
2d. Students know new combinations of
alleles may be generated in a zygote
through the fusion of male and female
gametes (fertilization).
2g. Students know how to predict
possible combinations of alleles in a
zygote from the genetic makeup of the
parents.
3a. Students know how to predict the
probable outcome of phenotypes in a
genetic cross from the genotypes of the
parents and mode of inheritance
(autosomal or X-linked, dominant or
recessive).
3b. Students know the genetic basis for
Mendel's laws of segregation and
independent assortment.
11-1 Key Words
•
•
•
•
•
•
•
•
•
Genetics
Fertilization
True-breeding
Trait
Hybrid
Gene
Allele
Segregation
Gamete
Quiz
on these
terms
Thursday!
11-1 The Work of Gregor
Mendel
Intro
Every living thingplant or animal,
microbe or humanhas a set of
characteristics
inherited from its
parents.
11-1
Definition
• Genetics: the scientific study
of heredity.
11-1
First clues to understanding
how traits are inherited came
from Gregor Mendel, an
Austrian monk, in the mid
1800’s.
His basic principles of
heredity are still
accepted today.
11-1
Mendel’s experiments:
• Unique
• 20,000 pea plants
because: • Used statistics
• Took detailed notes
11-1
Mendel’s experiments:
• Why peas?  Flower structure
– Mendel knew that
–the male part of each flower
produces pollen, (containing
sperm).
–the female part of the flower
produces egg cells.
• During sexual reproduction, sperm and egg
cells join in a process called fertilization.
• Fertilization produces a new cell.
11-1
Mendel’s experiments:
• Why
peas?
• Flower structure
• Presence of
distinctive traits
(wrinkled vs. smooth,
color, etc.)
• Fast reproduction
11-1
Genes and Dominance
A trait is a specific
characteristic that varies
from one individual to another.
11-1
11-1
Mendel’s work not recognized for
30 years (after his death).
That’s
just
wrong!
11-1
Gregor Mendel’s Peas
•Mendel had true-breeding pea plants that,
if allowed to self-pollinate, would produce
offspring identical to themselves.
•Mendel wanted to produce seeds by joining
male and female reproductive cells from two
different plants.
•He cut away the pollen-bearing male parts
of the plant and dusted the plant’s flower
with pollen from another plant.
•These were the “P” generation.
11-1
Gregor Mendel’s Peas
•This process is
called crosspollination.
•Mendel was
able to produce
seeds that had
two different
parents.
11-1
Pure lines
Seed
produced
11-1
Mendel’s experiments:
• What
did he
do?
• Seed was produced. This
seed was grown and
called the first filial or
“F1” generation.
All plants were tall when grown.
11-1
hybrids
F1
generation
11-1
Mendel’s F1 Crosses on Pea Plants
Hybrid
• The offspring of crosses between
parents with different traits
• Mendel’s F1 hybrid plants all had
the character of only one of the
parents.
11-1
Remember
what a
diploid
organism
is?
1 “allele”
from each
parent
Yy
11-1
Mendel's first conclusion was that
biological inheritance is determined
by factors that are passed from one
generation to the next.
Today, scientists call the factors that
determine traits genes.
11-1
that its
NoIsbaby,
shortness
trait
only hidden.
lost forever?
• Each of the traits Mendel studied was
controlled by one gene that occurred in
two contrasting forms that produced
different characters for each trait.
• The different forms of a gene are
called alleles.
11-1
• Mendel’s second conclusion is called the
principle of dominance.
• The principle of dominance states
that some alleles are dominant and
others are recessive.
11-1
• An organism with a dominant allele
for a trait will always exhibit that
form of the trait.
• An organism with the recessive allele
for a trait will exhibit that form only
when the dominant allele for that
trait is not present.
2 dominants  dominant
1 dominant + 1 recessive  dominant
2 recessive  recessive
11-1
What happens during segregation?
Segregation
Mendel crossed the F1 generation
with itself to produce the F2
(second filial) generation.
The traits controlled by recessive
alleles reappeared in one fourth of
the F2 plants.
11-1
Segregation
•Mendel's F2 Generation
P Generation
Tall
Short
F2 Generation
F1 Generation
Tall
Tall
Tall
Tall
Tall
Short
11-1
• Mendel assumed that a dominant
allele had masked the corresponding
recessive allele in the F1 generation.
• The trait controlled by the recessive
allele showed up in some of the F2
plants.
11-1
The reappearance of the trait
controlled by the recessive allele
indicated that at some point the allele
for shortness had been separated, or
segregated, from the allele for
tallness.
• Mendel suggested that the alleles for
tallness and shortness in the F1 plants
segregated from each other during the
formation of the sex cells, or gametes.
When each F1 plant flowers and
produces gametes, the two alleles
segregate from each other so
that each gamete carries only a
single copy of each gene.
Therefore, each F1 plant produces
two types of gametes—those with
the allele for tallness, and those
with the allele for shortness.
Alleles separate during gamete formation.
11-1
–
Gametes are also known as
• genes.
• sex cells.
• alleles.
• hybrids.
11-1
–The offspring of crosses between
parents with different traits are called
• alleles.
• hybrids.
• gametes.
• dominant.
11-1
In Mendel’s pea experiments, the male
gametes are the
• eggs.
• seeds.
• pollen.
• sperm.
11-1
In a cross of a true-breeding tall pea
plant with a true-breeding short pea
plant, the F1 generation consists of
• all short plants.
• all tall plants.
• half tall plants and half short plants.
• all plants of intermediate height.
11-1
If a particular form of a trait is always
present when the allele controlling it is
present, then the allele must be
• mixed.
• recessive.
• hybrid.
• dominant.
Gene-Chromosome Theory
25-1 in “Bear Book”
Mendel concluded that forms of
a trait must remain separate in
offspring.
Offspring receives 1 trait from
each parent.
Traits are coded for by genes.
25-1
Genes: sections of a
chromosome that code for a
trait.
25-1
Alleles
• To agree with Mendel’s
findings, each body cell should
have 2 copies of each trait
(alleles).
–e.g. 2 copies of the gene for
height
25-2
Different forms of a trait are
called alleles.
25-1
Alleles of 1 gene
25-2
Alleles
Homozygous
Dominant
Gene 1
A
Gene 1
A
Homologous pair
25-2
Alleles
Heterozygous
Gene 1
A
Gene 1
a
Homologous pair
25-2
Alleles
Homozygous
recessive
Gene 1
a
Gene 1
a
Homologous pair
25-2
Alleles
a
a
A
A
25-2
Anatomy of a
chromosome
One from mom, one from dad
(homologous
pair)
Gene for eye color:
Allele for brown eyes
}
Exact copies
(homologous
chromatids)
}
allele for blue eyes
25-1