7.1 key concept the chromosomes on which genes are located can affect the expression of traits
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7.1 KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits. Two copies of each autosomal gene affect phenotype. Mendel studied autosomal gene traits, like hair texture. (dominant). Mendel’s rules of inheritance apply to autosomal genetic disorders. - PowerPoint PPT PresentationTRANSCRIPT
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