Heredity PPT File Download

Transcript
Heredity: AKA
Inheritance
17.0 Analyze the relationships
within living systems
17.2 Examine the molecular basis of
heredity and resulting genetic
diversity.
Inheritance: the way genes are passed down.
• If a father
doesn’t have
a leg does
that mean his
children will
be born with
out a leg????
Hundreds of years ago people knew that somehow
certain traits would be passed on to their children.
Gregor Mendel was the first to predict the outcome
of inheritance. The study of inheritance is Genetics.
• Mendel did
several
different
experiments
on pea plant.
• This is an
example of
wrinkled and
smooth seeds.
Genes and Alleles
• A gene is a specific
piece of DNA.
• You have two genes
that code for the
same thing (ex.
Height). Each of
those two genes is
called an allele.
• So if something had
the genes Aa one
allele would be “A”
the other would be
“a”).
Why two alleles for every gene?
• Because organisms get
2 sets of chromosomes
……….one from the
mother and one from
the father.
Phenotype
• Is the physical
characteristics of the
trait.
• In most cases it is
what we can “see”.
• Example: Freckles,
dimples, attached
earlobes etc.
Genotype
• Is the actual alleles
that make up the trait.
• In most all cases this is
represented by 2
letters.
• Example: AA, Aa, aa
Dominant
• A dominant trait is a trait that
covers or hides the other trait of
an allele.
• For example, dark colors in hair
usually overshadow the other
allele.
• In this class Dominant will
always be represented with a
capital letter.
• Example: Say “D” is the allele
for black hair and “d” is the
allele for blond. The if an
animal had Dd then it would
have black hair.
Recessive
• A recessive trait is the
trait that is hidden by
the dominant trait.
• In an animal with Dd
for hair color the
recessive allele is “d”.
• The animal carries a
gene for blond hair but
you can’t tell by
looking at it.
Incomplete Dominance
• Sometime traits do not have one clear dominant
gene or one clear recessive gene
• In incomplete dominance, traits appear to blend
together
• When crossing a red snapdragon with a white
snapdragon, the offspring is pink if incomplete
dominance occurs
• The heterozygous genotype in incomplete
dominance appears different than either of the
homozygous alternatives
– Example: red – pink - white
Heterozygous
• This is the term given
two different alleles.
• For example, Aa is
heterozygous.
• It may contain one
gene for brown
eyes(A) from the
mother and one gene
for blue(a) eyes from
the father.
Homozygous
• This is the term given
to the two same
alleles.
• For example, AA or aa
• A person may contain
2 genes for -brown
eyes – one from each
parent (AA) or 2 for
blue (aa).
Can an Organisms Genotype or
Phenotype be predicted.
• Using genotypic and phenotypic ratios the
probability of a specific genotype or
phenotype appearing can be determined.
• A Punnet Square is used to determine these
ratios.
Punnett Squares
A
a
Parents alleles are:
AA and aa
a
Aa
a
Aa
aa
aa
Phenotypic and Genotypic Ratios
• Phenotypic Ratios
– Shows ratio of what is seen
• Example: previous Punnett square: the phenotypic
ratio is 2:2
• This means that the appearance of the offspring will
have a 50% chance to be of the Dominant trait A,
and 50% chance to be of the Recessive trait a.
Phenotypic and Genotypic Ratios
• Genotypic Ratios
– Shows the potential genetic make-up of the
offspring.
• Example: previous Punnett square: the genotype
ratio is 0:2:2
• Meaning the offspring will not be homozygous AA,
50% chance of being Heterozygous Aa, and 50%
chance of being homozygous aa.
Example
B
B
b
Bb
Bb
b
Bb
Bb
• Angus cattle: coat color
B is dominant
b is recessive
cross a BB cow with
a bb bull
Example
• What is the Phenotypic ratio?
• What is the Genotypic Ratio?
Example
• What is the Phenotypic ratio?
– 4:0 B - black
• What is the Genotypic Ratio?
– 0:4:0 Heterozygous Bb - Black
Example cont.
•
Bull - BbPp
BP
Bp BBPp
Bp BBPp
Bp
BBpp
bP
BbPp
bp
Bbpp
•
Polled:
•
P is dominant
p is recessive
•
BBpp BbPp
Cow - BBpp
Bbpp
Cross a BB cow to a Bb
bull. But also, another allele is
considered.
• Cross the Bb heterozygous
polled bull with the BB
homozygous recessive polled
cow
• All of the offspring have a
black phenotype only
Example cont.
BBPp – black polled
BBpp – black horned
BbPp – black polled
Bbpp – black horned
Phenotypic Ratio
4:0 - black
2:2 - polled
Genotypic Ratio
2:2:0 - Black
0:2:2 - Polled