Transcript Gregor Mendel and Genetics

Gregor Mendel and Genetics
Gregor Mendel was a Swiss Monk
who studied genetic traits in Pea
Plants
Inheritance
• We each inherit 2 forms of each gene
– 1 from each parent in the sex cells or
gametes (sperm and egg)
– The genes code for the same traits (eyes,
ears, fingers) but variations of those traits
– Blue or Brown eyes, hairy knuckles, non-hairy
knuckles, sickle cell /non-sickle cell
– These variants are called alleles
Types of Inheritance
• Complete dominance:
– One allele is dominant over the other –
inheriting only one dominant allele will show
this trait
– The other allele is considered recessive –
one needs to inherit this variant from both
parents
Eye color
• Eye color is a complete dominance
inheritance pattern:
• Brown is represented by B
• Blue is represented by b
• The genotype of a person with brown
eyes could be: BB or Bb
– One “B” from each parent and
– a second “B” or ‘b’ from each parent
• The phenotype of BB or Bb is brown eyes
Heterozygous and Homozygous
• If both copies of the allele are the same,
one is considered to be homozygous for
that trait (BB OR bb)
• If one has two different alleles for a gene
one is considered to be heterozygous for
that trait (Bb)
Mendel’s “Laws”
• Law of Independent Assortment
– Genes are usually inherited independent of
each other (so you can be tall and blond, etc)
– Mendel used Pea plants – he saw that each
trait (flower color, height, seed color, seed
shape) were all inherited separately from
each other
• Law of Segregation – The genes are
separated into gametes (sex cells) and
reunited during fertilization
Seed Shape
Pod Shape
Other Inheritance patterns
Co-Dominance – neither gene is completely
dominant – blood typing – type A, B, AB or i or
type O
• X- linked – traits carried on the X chromosome
• Women’s genotype is XX ( and X from each
parent)
• Men are XY – X from the mother, Y from father
• tend to be more likely in men because they
have only 1 X-chromosome.
X- linked traits
Women can be carriers –
because they can have an
X chromosome that
doesn’t have the trait
The trait won’t show but
they can pass it on
Diagramming X-Linkage
Female
XX
XY
Male
X-Chromosome/ Y Chromosome
Punnett Squares
• A heterozygous
parent has
genotype:
•
Bb
• A parent
homozygous for
blue eyes has
genotype:
•
bb
\
\
\
\
Genetics is about Probabilities
• Bb x bb
• Look at the boxes that • Phenotype
show all of the
probabilities- what
possible results:
they will look like:
• BB =
• Bb/bB =
• Bb =
• Genotype – what their
allele distribution is:
Heterozygous black guinea pigs are mated to
homozygous white guinea pigs. Do the
punnett square for this cross. (Use B for
black and b for white) Genotype Ratios
% BB
%Bb
%bb
Phenotype Ratios
% Black
% White
Genetics Is Probabilities
• Each mating is a new
“throw of the dice”
• Every time it is the
same
• Women are XX
• Men are XY
• XY x XX
• What are the chances
of having a boy?
Monohybrid Crosses
• When we look at the inheritance patterns
of a single gene we call this a monohybrid
cross
• When we look at the inheritance patterns
of two genes at the same time we call this
a dihybrid cross
How we indicate a X-linked trait
• We use a regular X with a subscript
Indicator letter:
Hemophilia is indicated
As
Xh - it is recessive
XhY – This male will have hemophilia
Xh X – This female will not have hemophilia
Hemophilia – X-linked trait
•
•
Hemophilia is a disease of bleeding.
Why is it called an “X-linked” trait?
•
Xh – to show that the gene for hemophilia
is on the chromosome.
Other Inheritance Patterns:
Co –Dominance – Neither trait is fully
dominant over the other (usually found in
Blood Types)
• Incomplete dominance – There is some
blending in the resulting traits – found in
fur and feather color in some animals:
There is a breed of chickens called “blues”
– crossing a black
Carriers
•
•
•
•
Hemophilia is a recessive gene – it
needs to be on both X chromosomes for
a female to have the disorder. If only 1
chromosome has it she is a Carrier
We indicate a carrier this way:
XXh – Notice only 1 of the X
chromosomes carries the disorder
XhXh - Female who HAS the disorder
Females are Carriers
•
Why can’t males be carriers?
•
We indicate a male with hemophilia this
way:
XhY
•
Dihybrid Crossing
• What happens when you look at 2 different
traits?
When Mendel looked at the inheritance
of two separate traits, he discovered that
the outcome for each trait was unchanged
from his examination of individual traits.
He determined that most traits are
inherited independently of others. This
became his Principle of Independent
Assortment
There are 4 different
ways that the alleles
for the seed color and
seed shape can be
combined.
RY rY Ry ry
These 4 possible
combinations can
result in 16 different
genotypes
R = Round r = wrinkled
Y = Yellow y = green
Of the sixteen possible outcomes:
How many are round and yellow?
How many are wrinkled and yellow?
How many are round and green?
How many are wrinkled and green?
Which color is dominant? __________
Which shape is dominant?
________________________
Punnett squares
A female carrier and
a normal male:
Female carrier
______
Normal Male
_________
Phenotype Ratios:
• Affected Males:
Female carriers
• Affected Females
• Genotype Ratios:
• XY _____
Xhx _____
• XX_____
XhXh___
Probability of having a child with hemophilia
Pedigrees
• Which are the males?
• Which are the females?
• Which is the unaffected
family member?
= affected
female
= affected
male
= unaffected
female
= unaffected
male
• What kind of inheritance
is this?
Solving a Pedigree Problem
• A)What are the likely
genotypes of III1 and III2?
• B) What are the likely
genotypes of offspring of III1
and III2?
The black hair of guinea pigs is produced by a dominant gene B
and white by its recessive allele b.
Assume that II1 and II4 do not carry the recessive allele.
Using this hint – Use text boxes to write the
genotypes that you can determine