types of inheritance patterns
DESCRIPTION
Types of Inheritance Patterns. Gene Linkage. Genes on the same chromosome are considered linked and are called a linkage group. Human Sex-linked Inheritance. Sex-linked traits are distinguishable by their mode of transmission through successive generations of a family. - PowerPoint PPT PresentationTRANSCRIPT
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Types of Inheritance Patterns
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Gene Linkage
Genes on the same chromosome are considered linked and are called a linkage group.
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Human Sex-linked InheritanceSex-linked traits are distinguishable by their mode of transmission through successive generations of a family.
In humans it is preferable to speak in terms of X-linked or Y-linked inheritance.
Red-green color blindness was the first human trait proven to be due to a gene on a specific chromosome. Hemophilia is another common sex-linked trait.
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Sex-Linked Traits
If a gene is found only on the X chromosome and not the Y chromosome, it is said to be a sex-linked trait. Because the gene controlling the trait is located on the sex chromosome, sex linkage is linked to the gender of the individual.Usually such genes are found on the X chromosome. The Y chromosome is thus missing such genes.
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The result is that females will have two copies of the sex-linked gene while males will only have one copy of this gene. If the gene is recessive, then males only need one such recessive gene to have a sex-linked trait rather than the customary two recessive genes for traits that are not sex-linked.This is why males exhibit some traits more frequently than females.
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Examples of Sex-linked Traits:
Red-green colorblindnessMale Pattern BaldnessHemophiliaDuchenne Muscular Dystrophy
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Chromosome Mapping
A chromosome map is a linear diagram of the position of the alleles on a chromosome.
The closer together the genes are linked on the chromosome the less chance they will separate during crossing over.
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The map distance is the distance between genes on a single chromosome.
The greater the distance between linked genes, the more likely they are to cross over during meiosis.
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Sample Sex-linked Trait Problems
In humans, red-green colorblindness is a recessive sex-linked trait. It is found on the X chromosome, not the Y. Because, males only have one X chromosome, they have a much greater chance of having red-green colorblindness. Females would have to be homozygous recessive in order to have red-green colorblindness
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Multiple Alleles and Blood Types
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Pedigree
* is a tool that can determine the pattern of inheritance of a particular trait.
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Multiple Alleles Within a
population, more than two alleles can exist (although any given individual only has two alleles).
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The human ABO blood groups are an example of multiple alleles, and the relationship between phenotype and genotype.
There are four possible phenotypic blood types for this particular gene: A, B, AB, and O. The letters refer to two specific antigens on the surface of red blood cells.
Individuals can have the A antigen (blood type A), the B antigen (blood type B), both the A and B antigen (blood type AB), or neither antigen (blood type O).
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Human blood type is determined by codominant alleles. There are three different alleles, known as IA, IB, and i. The IA and IB alleles are codominant, and the i allele is recessive.
The possible human phenotypes for blood group are type A, type B, type AB, and type O. Type A and B individuals can be either homozygous (IAIA or IBIB, respectively), or heterozygous (IAi or IBi, respectively).
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Cross Type AB and a Type O blood What are the possible blood types of the
offspring of a cross between individuals that are type AB and type O? (Hint: blood type O is recessive)
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Type A and type B cross Four different
genetic crosses are possible. All four crosses must be considered to determine all potential offspring. However, one cross (IAi mother x IBi father) is most informative.
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Types of Inheritance patterns
Autosomal Dominant Inheritance • using chromosomes
other than sex chromosomes
• the traits would be either dominant or recessive
• whenever a recessive phenotype occurs in a child of parents who exhibit the dominant trait, the parents must be heterozygous for that trait
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Autosomal Recessive Inheritance
deals with autosomes with the recessive genes being inherited