Download St.2 Notes-GeneticsHeredity.cwk (WP)

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Combination Notes for Standards): 2b,2c,2d,2e Genetics and Heredity
Textbook Resources: Chapter(s)/Section(s) Ch. 6.1, 6.2, 6.3, 7.1--page 189
Concept: Genetics/Heredity
written details, facts, definitions etc.
Drawings/Examples to help improve
understanding of the concept.
eye color is
an inherited
trait
Genetics is the scientific study of how
inherited traits are passed from parents to
offspring on the chromosomes (or genes).
Genetic science studies “heredity”
Heredity is the passing of inherited traits (like
eye color, hair color, flower color etc.) from
parents to offspring.
having freckles is an
inherited trait
An inherited trait is a characteristic that an
organism can pass on to its offspring through
its genes.
Brad Pitt has
dimples,
dimples are
inherited
Mendel studied pea plant traits such as flower
color pea shape, stem height, pod color, etc.
Concept: Chromosomes
written details, facts, definitions etc.
A chromosome is a cell structure made of
condensed chromatin (DNA) and proteins.
Drawings/Examples to help improve
understanding of the concept.
chromosome
Chromosomes carry genes and their traits
from parents to offspring.
Chromosomes can contain thousands of
different genes
gene
Humans have 46 chromosomes in their cells
which are found in pairs (23 pair)
An offspring inherits half of its chromosomes
from the male parent, and half its
chromosomes from the female parent
In humans, females have 2 “X”
chromosomes, while males have an “X”
chromosome and a “Y” chromosome. So,
your dadʼs chromosome determined whether
you were a boy or a girl.
A gene is a segment of DNA on a
chromosome.
Each gene has two copies (one
copy on each chromosome the
organism inherited from its two
parents)-the copies of the gene are
called alleles.
Concept: genes/alleles
written details, facts, definitions etc.
Genes are segments of DNA on a chromosome
that pass on inherited traits.
There are two copies of each gene (one from
each parent)
The combination of the 2 genes (or alleles)
that an individual inherits determines the
traits the individual has.
The copies of a gene are called alleles.
Drawings/Examples to help improve
understanding of the concept.
A gene is a segment of DNA on a
chromosome.
Each gene has two copies (one
copy on each chromosome the
organism inherited from its two
parents)-the copies of the gene
are called alleles.
one
chromosome
from the
male parent
2 copies of the same
gene
one
chromosome
from the
female parent
The two alleles together make up the
genotype for the trait.
Alleles are shown as letters when writing
about them: a capital letter represents a
dominant allele, while a lower case letter
represents a recessive allele
the 2 copies are called alleles
Concept: dominant allele/recessive allele
written details, facts, definitions etc.
Drawings/Examples to help improve
understanding of the concept.
An allele is one copy of a gene (a gene has
two copies)
An allele can be dominant or recessive
There only needs to be one dominant allele in
the genotype for the dominant form of the
trait to show up in the phenotype of the
organism (the other allele could be
dominant, or recessive).
If an organism has two dominant alleles for a
trait (such as TT for tall stems) the plant will
be tall.
If an organism has only one dominant allele,
and the other is recessive (Tt) the plant will
still be tall because the dominant allele will
hide or mask the recessive allele.
A recessive trait is controlled by a recessive
allele, so the only way a recessive trait, like
short stems in pea plants, will show up is if
the genotype is (tt)
one allele might be dominant, and the
other might be recessive (Aa), or the
alleles could both be the same (AA or aa)
homologous chromosomes (one
from each parent)
The arrows point
only to the copy of
the gene or allele on
one chromosome.
The other chromosome has the other
copy of the gene--or the other allele.
Each gene has two copies (one copy
on each chromosome the organism
inherited from its two parents)the copies of the gene are called
alleles--the two copies of the gene (or
the two alleles) control the same trait.
Concept: genotype
written details, facts, definitions etc.
Drawings/Examples to help improve
understanding of the concept.
The genotype is the combination of genes (or
two alleles) for a genetic trait
A homozygous genotype means
both alleles are the same:
Genotypes are written as two letters, one for
each allele
For example two dominant alleles
for purple flowers would be
written as: PP
The combination of the 2 alleles that an
individual inherits is determined completely
by random chance.
There are only 3 possible genotypes for all the
traits studied by Mendel
Tt, TT, or tt
The first genotype includes one dominant
(tall stems) and one recessive allele (short
stems). The second genotype includes two
dominant alleles (tall stems). The third
genotype includes two recessive alleles (short
stems)
Concept: phenotype
written details, facts, definitions etc.
The word phenotype refers to an organismsʼ
appearance or other detectable
characteristics.
two recessive alleles for white
flowers would be written as: pp
A heterozygous genotype means
the two alleles are different:
For example the genotype Pp
means the plant has one
dominant, purple flower allele (P),
and one recessive, white flower
allele (p)
The genotype Tt means the plant
has one tall stem allele (T for
dominant) and one short stem
allele (t for recessive)
Drawings/Examples to help improve
understanding of the concept.
Examples of genotypes and
phenotypes in pea plants
Genotype
Phenotype
The phenotype is sort of like the “physical”
appearance, or the visible traits
PP
Pp
purple flowers
purple flowers
The phenotype is determined or caused by
the genotype.
pp
white flowers
If a pea plant has the genotype of “Tt”, or
“TT”, then it would “look” tall, you could
actually see that it is tall--that is the
phenotype (but it IS tall because of the
genotype which you can not see.
GG
Gg
green pods
green pods
gg
yellow pods
If a pea plant has the genotype of “tt” then
when you look at it you see a plant with
short stems (it only has two recessive short
stem alleles in its genotype)
The phenotype is
the actual, visible trait
yellow pods, or purple
flowers etc.
Concept: self-pollination/true breeding/purebred
written details, facts, definitions etc.
Drawings/Examples to help improve
understanding of the concept.
The pea plants Mendel studied were selfpollinating which means that they had both male
and female reproductive structures on the same
flower.
True-breeding and self pollinating plant.
The plants were also True-breeding which means
that they were purebred.
Genotype of the offspring could only
be PP
This basically means that for any given trait, for
example, flower color, the plant only had
dominant alleles. The male pollen/sperm had two
alleles for purple flowers, and the female egg had
two alleles for purple flowers. No matter which
of the two alleles the egg or sperm passed on, it
could only be a dominant purple allele. This
means the offspring would always have the same
trait as the parent plant.--so the parent(s) are
true-breeding or purebred.
Genotype= pp for the sperm
pp for the egg
Mendel only used the true-breeding plants to be
sure of their traits before he started his first
experiments. In his next experiments he did not
allow the plants to self-pollinate.
Concept: cross pollination
written details, facts, definitions etc.
In Mendelʼs first experiments he did not
allow the plants to self-pollinate.
Instead he cut the anthers (the sperm
producing part of the plant) off so the plants
could not pollinate or fertilize themselves.
Genotype = PP for the sperm
PP for the egg
Genotype of the offspring could only
be pp
The parent plant would be considered
purebred because it is homozygous for
the trait (both alleles are the same).
If the purple flower is selfpollinating, and true breeding all its
offspring will ALWAYS be purple
Drawings/Examples to help improve
understanding of the concept.
The purple flower pollinates the white
flower of a different plant-this is cross
pollination
X
Two different plants that are both purebred
for the trait are still considered True-breeding,
even if they cross pollinate.
He took the sperm from one plant and used it
to pollinate and fertilize the eggs from a
different plant.
This is known as cross-pollination--Pollen
from one plant pollinates a different plant.
= cross
pollination
X
= cross pollination
all offspring will ALWAYS have white
flowers
X
= cross pollination
Pp
Pp
some offspring will have purple
flowers other offspring could have
white flowers
Concept: Punnett square
written details, facts, definitions etc.
Drawings/Examples to help improve
understanding of the concept.
A Punnett square can be used to find the most
likely outcomes (probability) of a genetic cross
of two parents.
The Punnett square shows the genotype for
one parent along the top, and the genotype of
the other parent along the side.
male parent (PP)
female
parent
(Pp)
All the possible ways the alleles of each parent
can combine can be shown in the four “inside”
boxes of the Punnett square.
The 4 inside boxes represent the possible
genotypes that can be present in the offspring.
The Punnett square only shows what the
mathematical probabilities are--it does not
show what WILL definitely happen--only what
is most likely to happen.
The two upper boxes in the Punnet square
have homozygous genotypes in them (PP)
The two lower boxes in the Punnett square
have heterozygous genotypes in them (Pp)
P
p
P
P
PP
PP
Pp
Pp
The four inner boxes show the possible
genotypes for the offspring of this “Genetic
cross” (cross breeding of two different
parents)
The genotypes of the parents are shown
outside the Punnett square.
This genetic cross results in only two different
possible genotypes in the offspring. PP or
Pp. All the offspring resulting from this
cross will be purple (even though
Another genotype (not possible in this cross) is genetic
they
might
have different genotypes).
homozygous for both recessive alleles (pp)
Use the space below for Punnett Square Practice Problems