Download Mendelian Genetics

Mendelian Genetics
Mendelian Genetics
• Heredity – the passing of traits from
parents to offspring
• Genetics: The scientific study of
heredity
Mendelian Genetics
• Chromosomes- rod-shaped structures in
the nucleus that transmits genetic
information
• Genes- units of hereditary information
found on the chromosomes
Important Vocabulary
• dominant- a gene that masks the expression of
another gene in a pair (Symbol- capital letter)
• recessive- a gene in a pair that is hidden by
the dominant gene (Symbol- lower case letter)
Parent 1
R = red
dominant
Parent 2
r = yellow
recessive
Offspring
Red (Rr)
dominant
Important Vocabulary
• Homozygous- two genes in a pair that
are identical.
Ex. Homozygous dominant- RR GG
Homozygous recessive- rr gg
• Heterozygous- individual with one
dominant and one recessive
gene in a pair.
Ex. Rr or Gg
Important Vocabulary
Identify each of the pairs below as
homozygous dominant, homozygous
recessive, or heterozygous.
Yy Heterozygous
rr Homozygous recessive
Tt Heterozygous
SS Homozygous dominant
TT Homozygous dominant aa Homozygous recessive
Bb Heterozygous
Ss Heterozygous
Important Vocabulary
• Allele- each form of a gene for a certain trait .
Ex. B = dominant allele (brown eyes)
b = recessive allele (blue eyes)
Important Vocabulary
• Genotype- the pair of alleles represented
by the capital and lower case letters.
• Phenotype- the trait that is actually
expressed in an organism
Examples
Genotype
Phenotype
YY
yellow seeds
Yy
yellow seeds
yy
green seeds
Important Vocabulary
• Examples of genotype and phenotype
Important Vocabulary
• Examples of genotype of phenotype
Figure 14.5 Genotype versus phenotype
Inheritance
• You get your genes from your parents
• In meiosis, half of the chromosomes in a
pair come from the Dad, half come from
the Mom
• What we know today is based on the work
of Gregor Mendel
1856-1865
Gregor Mendel
-Austrian Monk
– pea plants in monastery garden
– COUNTED the plants and compiled data
(QUANTITATIVE APPROACH to science)
Paper was published in 1866,
but not enough was understood
to truly value this work.
Today known as
father of modern genetics
Mendel chose to use plants that
were true-breeding…
• P generation – parentals; true-breeding
(On their own create identical offsprings)
parents that were cross-pollinated
• F1 generation – hybrid offspring of
parentals that were allowed to selfpollinate
• F2 generation – offspring of F1’s
*Flower color : purple (P) vs. white (p)
PP x pp
All Pp
PP, Pp & pp
Figure 11-3 Mendel’s Seven F1
Crosses on Pea Plants
Section 11-1
Go to
Section:
Seed Coat
Color
Pod
Shape
Pod
Color
Smooth
Green
Seed
Shape
Seed
Color
Round
Yellow
Gray
Wrinkled
Green
White
Constricted
Round
Yellow
Gray
Smooth
Flower
Position
Plant
Height
Axial
Tall
Yellow
Terminal
Short
Green
Axial
Tall
Mendel’s 3 principles
• Principle of Dominance- one factor (gene) in a
pair may prevent the other factor (gene) in a pair
from being expressed.
P
Parental
Round
RR
Wrinkled
rr
RR
F1
First Filial
All Round
Rr
F2
Second Filial
Mendel’s 3 principles
• Principle of Segregation- the members
of each pair of genes separate, or
segregate, when gametes are formed.
RR
R
Rr
rr
R
Rr
Parents
r
r
Gametes– genes
Rr
Rr
Offspring
Gene pairs
Mendel’s 3 Principles
Principle of Independent Assortmenttwo or more pairs of genes segregate
independently of one another during the
formation of gametes
In other words…..
Just because a seed is round does not
mean that it has to be yellow.
Mendel’s 3 principles
• Principle of Independent Assortment
RrYy
RY
Yellow
Round
Ry
Green
Round
R = round
r = wrinkled
Y = yellow
y = green
rY
ry
Yellow
Green
Wrinkled Wrinkled
Punnett Square
• Device for predicting the results of a genetic
cross between individuals of a known
phenotype.
• Example
Character – flower color
Alleles – Purple (P) and white (p)
Note: Purple is dominant with a capital letter and
white is recessive shown with a lowercase of
dominant trait
Genotypic combos possible –
two dominants: PP (homozygous dominant)
two recessives: pp (homozygous recessive)
One of each:
Pp
(heterozygous)
Monohybrid crosses –
only one character considered
Steps to do:
•
Write out genotypes of parents
•
Write out possible gametes produced
•
Draw 4 box Punnett square
•
Put one parent on the left side and one parent across the top
•
Fill in boxes
•
Determine genotypes by reading Punnett starting from top left
•
Determine phenotypes by reading from genotype list
Punnett Square Practice
Violet flowers are dominant to white flowers.
Diagram a Punnett Square for 2 heterozygous
flowers.
What is the parents’
V
v
V VV
Vv
v Vv
vv
genotype(s)? Vv
What is the parents’
phenotypes(s)? violet
What is the genotypic ratio
for the offspring? 1:2:1
What is the probability of
producing a white flower?
(In percent) 25%
Punnett Square Practice
Black rabbits are dominant over brown rabbits.
A heterozygous male is crossed with a brown
female.
What is the mother’s
flowers.B
genotype?
bb
b
b Bb
bb
b Bb
bb
What is the father’s
genotype?
Bb
Diagram a Punnett Square
for this cross.
What is the genotypic ratio? 1:1
What is the phenotypic
ratio?
1:1
Dihybrid (Two-Factor)Cross
• Because genes separate independently we
can determine the possible outcomes of a
two-factor cross.
• Example: Guinea pig hair color and length
– B- black b- brown
– S- short s- long
F1 Hybrids for Hair Color and Length: BbSs
FOIL – First, Outer, Inner, Last
Possible gametes passed on to offspring:
BS, Bs, bS, and bs –place in punnett square
Dihybrid
Crosses
BbSs x BbSs
Dihybrid Cross
• Example: Watermelon color and shape
– G- green g- striped
– S- short s- long
– Cross two Hybrids for Shape and Color: GgSs
GS
GS GGSS
Gs
gS
GGSs GgSS
gs
GgSs
Gs GGSs GGss
GgSs Ggss
gS GgSS
GgSs
ggSS
ggSs
gs GgSs
Ggss
ggSs
ggss
Dihybrid Cross
• Now that the Punnett square is complete,
determine the Phenotypic ratio
9
_______Green, short
GS
Gs
gS
gs
3
_______Green,
long
GGSS
GGSs
GgSS
GgSs
Green, short Green, short Green, short Green, short
3
_______Striped,
short
GS
1
_______Striped,
long
GGSs
GGss
GgSs
Ggss
Gs
Green, short Green, long
Green, short Green, long
Therefore, the ratio is:
9:3:3:1
gS
GgSS
GgSs
ggSS
ggSs
Green, short Green, short Striped, short Striped, short_________________
gs
GgSs
Green, short
Ggss
ggSs
ggss
Green, long Striped, short Striped, long
Beyond Dominant and Recessive
• Incomplete Dominance
One allele is not completely dominant over
the other – something in the middle is
expressed
Ex. Red and White Snapdragons –
Make Pink (Like mixing paints)
p. 272 in your book
Red – RR White – WW Pink – RW
Only one phenotype for each one genotype
Codominance
• Codominance
Both alleles are expressed in the phenotype
Ex. Cow Hair Color
RR – Red
WW – White
RW – Roan
(Red & White)
Incomplete Dominance
Example: Flower color is an incomplete
dominant trait. One red gene and one white
gene produces a pink flower.
• Cross two pink flowers. 1. What is the parents’
R
W
R RR RW
W RW WW
genotype? RW
2.What is the parents’
phenotype? Pink
3. What is the genotypic ratio
for this cross? 1:2:1
4. What is the phenotypic ratio
for this cross? 1:2:1
5. What is the probability of
producing a red flower? 25%
6. What is the probability of
producing a pink flower? 50%
Beyond Dominant and Recessive
• Multiple Alleles
Genes have more then
two alleles
Ex. Blood Type
Color Coats in Rabbits
A and B are also
codominant
Blood types
• Diagram a cross for a man with blood type
AB and a woman with blood type O.
A
B
O AO BO
O AO BO
What is the children’s
genotype(s)? AO, BO
What is the children’s
phenotypes(s)? Blood type A or B
What is probability of
producing a child with blood
type O? (in percent) 0
What is the probability of
producing a child with blood
type B? (In percent) 50%
Sex-linked traits
• Sex-linked traits- traits that are controlled by
genes found on the sex chromosomes. The X
chromosome contains the gene and the Y
chromosome does not.
• How many pairs of chromosomes do humans
have? 23 (46 total)
• What is the difference between male and
female chromosomes? Pair # 23
Female – XX and Male – XY
Karyotype – Picture of
Chromosomes
#1-22 are
Autosomal
#23 is a Sex
Chromosomes
Is this karyotype for
a male or female?
Sex-Linked Genes
• Ex. Colorblindness is carried on the sexchromosomes
• It is a recessive trait
What about genes located on the
sex chromosomes?
• Very few genes are located on the Y
chromosome……Most are located on the X
• So females carry two genes and males only
carry one.
• Draw a punnett square with the sex
chromosomes……XX x XY
Link the gene to the X only. EX: XCXC
or XCY
Sex-Linked Genes
• Ex. Colorblindness is carried on the sexchromosomes
• It is a recessive trait – Xc
How many genes do females need to
express the trait (colorblindness)?
2 Xc Xc
How many genes do males need to
express the trait (colorblindness)?
1 XcY
Side note…..
• If a female is XCXc then she is called a
carrier. She carries the recessive allele,
but does not express it.
Sex-Linked Punnett Square
• C – Normal Vision and c - Colorblind
C c
c
• X Y crossed with X X - colorblind Male x Carrier Female
Xc
Y
1. What is the female’s genotype?XCXc
C
X
C c
X X
C
X Y
2. What is the male’s genotype? XcY
3. What is the probability of producing a
colorblind child?
X
c
c
X X
c
c
X Y
50%
4. What is the probability of producing a
colorblind female?
50%
5. What is the phenotypic ratio for this
cross?
1:1:1:1
Pedigrees
Pedigree- Diagram showing the inheritance of a
trait in a family
*Colored
boxes and
circles show
the trait
Pedigrees
• Family history that shows how a trait is inherited
over several generations.
• Carriers: those heterozygous for a trait.
• Can determine if
–
–
–
–
autosomal (occurs equally both sexes)
sex-linked (usually seen in males)
heterozygous (dominant phenotype)
homozygous (dominantdominant phenotype,
recessive recessive phenotype)
Pedigree Symbols
• affected individuals
have at least one
affected parent
• the phenotype
generally appears
every generation
• two unaffected
parents only have
unaffected offspring
• unaffected parents
can have affected
offspring
• affected progeny are
both male and female
Sex-linked Recessive
Pedigrees
• Curly hair is dominant
and straight hair is
recessive. The
colored figures in the
pedigree show which
individuals have
straight hair.
Determine the
genotypes and
phenotypes for the
pedigree in the
diagram
cc
straight
Cc
curly
Cc
curly
Cc
curly
?
cc
cc
curly straight straight
cc
?
cc
Cc
?
Cc
straight curly straight curly curly curly