Download - 7.1 KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits
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
• Mendel’s rule only apply for autosomal genes(chromosome pairs 1-22). Genes on sex chromosomes are called sex-linked 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 sex-linked genes are expressed.
– In females, expression of sex-linked 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
• In incomplete dominance, neither allele is completely dominant nor completely recessive.
Ch. 7: Extending Mendelian Genetics
• Codominant alleles will both be completely expressed.
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 :
• Genotyple: IAIA or IAi• Antigen: A
• Antibody: Anti-B
• Can receive from: A, O
• Can donate to: A, AB
Ch. 7: Extending Mendelian Genetics
B :• Genotyple: IBIB or IBi• Antigen: B
• Antibody: Anti-A
• Can receive from: B, O
• Can donate to: B, AB
Ch. 7: Extending Mendelian Genetics
AB :• Genotyple: IAIB
• Antigen: A & B
• Antibody: none
• Can receive from: A, B, AB, & O (universal recipient)
• Can donate to: AB
Ch. 7: Extending Mendelian Genetics
O :• Genotyple: 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-
• Antigen: Rh
• Antibody: none
• Can receive from: Rh+ & Rh-
• Can donate to: Rh+
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 alleleBlack is dominant to chocolate B or bYellow is recessive epistatic (E or e)
PhenotypePossible Genotypes
BBEE BbEE BBEe BbEe
bbEEbbEe
BBeeBbeebbee
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 karyotype is a picture of all chromosomes in a cell.
X Y
Ch. 7: Extending Mendelian Genetics
• Karyotypes can show changes in chromosomes.
– Nondisjunction: an error in meiosis that results in an extra or a loss of a chromosome
– deletion of part of a chromosome or duplication of part of a chromosome
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
• 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