Download Ch. 7: Extending Mendelian Genetics

Ch. 7: Extending Mendelian Genetics
7.1 KEY CONCEPT
The chromosomes on which genes are located can
affect the expression of traits.
Ch. 7: Extending Mendelian Genetics
Two copies of each autosomal gene affect phenotype.
• Mendel studied autosomal
gene traits, like hair texture.
Ch. 7: Extending Mendelian Genetics
• Mendel’s rules of inheritance apply to autosomal
genetic disorders.
– Recessive disorder requires a homozygous recessive
genotype to affect a person. A heterozygote for a
recessive disorder is a carrier.
– Disorders caused by dominant alleles are uncommon.
(dominant)
Ch. 7: Extending Mendelian Genetics
• Codominant alleles
• Two equally dominant alleles are expressed at the same
time.
• Heterozygous phenotype will have both phenotypes
visible
Ch. 7: Extending Mendelian Genetics
Shorthorn Cattle
• Co- dominance
• Homozygous red (RR)
• Homozygous white (WW)
The offspring of will have both red and white hairs (RW)
The offspring are heterozygous and called “roan”
Ch. 7: Extending Mendelian Genetics
Sickle- Cell Anemia
• Co- dominance
• Caused by an abnormal
Hemoglobin, the protein that
red blood cells use to carry
oxygen
Normal hemoglobin is (RR)
Sickle Cell shaped blood cells (SS)
People who are carriers (heterozygous) for the
disease there is a mixture of both normal and sickle
cell (RS)
Ch. 7: Extending Mendelian Genetics
• In incomplete dominance
• Neither allele is completely dominant over the other
allele.
• A heterozygous phenotype
– A mixture or blending of the two
Ch. 7: Extending Mendelian Genetics
Four-o’ clock flowers
• Incomplete dominance
• Neither Red (R)
• or White (W) is dominant
When a homozygous red flower (RR)
Mix with a homozygous white flower (WW), the alleles
blend in the hybrid (RW) to produce pink flowers
Ch. 7: Extending Mendelian Genetics
Andalusian Chickens
• Incomplete dominance
• Neither Black (B) or
White (W) are dominant
The offspring of a black feathered chicken (BB) and a white
feathered chicken (WW) are blue (BW) – BLUE HEN!!
Ch. 7: Extending Mendelian Genetics
• Mendel’s rule only apply for autosomal genes(chromosome
pairs 1-22). Genes on sex chromosomes are called sexlinked genes.
– Y chromosome genes in mammals are responsible for
male characteristics. Males have an XY genotype.
– X chromosome genes in mammals affect many traits.
Females have an XX genotype.
Ch. 7: Extending Mendelian Genetics
– Because males only
have one copy of
the X chromosome
all of a male’s sexlinked genes are
expressed.
– In females,
expression of sexlinked genes is
similar to autosomal
genes because they
have two copies of
the X chromosome.
Ch. 7: Extending Mendelian Genetics
– Common examples of sex-linked disorders:
• Duchenne’s muscular dystrophy
• Hemophilia
• Color Blindness
Ch. 7: Extending Mendelian Genetics
Ch. 7: Extending Mendelian Genetics
Normal Color Vision
Red-Green Color Blind
Left
Right
Left
Right
Top
25
29
Top
25
Spots
Middle
45
56
Middle
Spots
56
Bottom
6
8
Bottom
Spots
Spots
The test to the left is simpler.
The individual with normal color vision
will see a 5 revealed in the dot pattern.
An individual with Red/Green (the most
common) color blindness will see a 2
revealed in the dots.
Ch. 7: Extending Mendelian Genetics
– X chromosome inactivation randomly “turns off” one X
chromosome.
Ch. 7: Extending Mendelian Genetics
• Codominant alleles will both be completely expressed.
– Codominant
alleles are
neither
dominant nor
recessive.
– The ABO blood
types result
from
codominant
alleles.
• Many genes have more than two alleles.
Ch. 7: Extending Mendelian Genetics
• There are 3 alleles that determine blood type: IA, IB, and i
– IA and IB are dominant to i.
– IA and IB are codominant.
Ch. 7: Extending Mendelian Genetics
Codominance
Ch. 7: Extending Mendelian Genetics
– There are 4 blood types:
A:
• Genotype: IAIA or IAi
• Antigen: A
• Antibody: Anti-B
•
Can receive from: A, O
•
Can donate to: A, AB
Ch. 7: Extending Mendelian Genetics
B:
• Genotype: IBIB or IBi
• Antigen: B
• Antibody: Anti-A
•
Can receive from: B, O
•
Can donate to: B, AB
Ch. 7: Extending Mendelian Genetics
AB :
• Genotype: IAIB
• Antigen: A & B
•
Can receive from: A, B, AB, & O
(universal recipient)
• Antibody: none
•
Can donate to: AB
Ch. 7: Extending Mendelian Genetics
O:
• Genotype: ii
• Antigen: none
• Antibody: Anti-A and Anti-B
•
Can receive from: O
•
Can donate to: A, B, AB, & O
(universal donor)
Ch. 7: Extending Mendelian Genetics
• Rh Factor: Another surface marker which may or may
not be present on the RBC.
Ch. 7: Extending Mendelian Genetics
Rh+ :
• Genotype: Rh+Rh+ or Rh+Rh
• - Can receive from: Rh+ & Rh• Antigen: Rh
• Can donate to: Rh+
• Antibody: none
Ch. 7: Extending Mendelian Genetics
Rh- :
• Genotype: Rh-Rh• Antigen: none
• Antibody: Rh+
•
Can receive from: Rh-
•
Can donate to: Rh- & Rh+
Ch. 7: Extending Mendelian Genetics
• Many genes have more than two alleles or multiple
alleles used to express a trait.
Ch. 7: Extending Mendelian Genetics
• Polygenic traits are
produced by two or
more genes.
Order of dominance:
brown > green > blue.
Ch. 7: Extending Mendelian Genetics
Ch. 7: Extending Mendelian Genetics
• An epistatic gene can interfere with other genes.
Ch. 7: Extending Mendelian Genetics
Epistatic: recessive trait blocks another allele
Black is dominant to chocolate B or b
Yellow is recessive epistatic (E or e)
Phenotype
Possible
Genotypes
BBEE
BbEE
BBEe
BbEe
bbEE
bbEe
BBee
Bbee
bbee
Ch. 7: Extending Mendelian Genetics
Phenotype can be a combination of genotype and
environment.
Malnourished
Fed and cared for.
Identical twins separated at
birth and treated differently.
Ch. 7: Extending Mendelian Genetics
7.4 KEY CONCEPT
A combination of methods is used to study human
genetics.
Ch. 7: Extending Mendelian Genetics
A pedigree is a chart for tracing genes in a family.
• Phenotypes are used to infer genotypes on a pedigree.
• Autosomal genes show different patterns on a pedigree
than sex-linked genes.
Ch. 7: Extending Mendelian Genetics
• Squares represent
males and circles
females.
• A coloured in shape
means that person has
the trait in question.
• A half coloured in
shape means that they
are carrying an allele
for a recessive trait.
Ch. 7: Extending Mendelian Genetics
• If the phenotype is more common in males, the gene is
likely sex-linked.
Ch. 7: Extending Mendelian Genetics
7.3 KEY CONCEPT
Genes can be mapped to specific locations on
chromosomes.
Ch. 7: Extending Mendelian Genetics
• Because of their location on a chromosome, some genes
travel together and are considered to be linked.
Wild type
Mutant
Ch. 7: Extending Mendelian Genetics
Linkage maps estimate distances between genes.
• The closer together two genes are, the more likely
they will be inherited together.
• Linkage maps show the relative locations of genes.
Ch. 7: Extending Mendelian Genetics