Mendelian Inheritance Patterns and Genetic Diseases

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Questions and Answers

What is the effect of conditional lethal alleles on an organism, and under what conditions do they occur?

Conditional lethal alleles kill an organism only when certain environmental conditions prevail, such as temperature-sensitive alleles.

What is the difference between semi-lethal alleles and lethal alleles?

Semi-lethal alleles kill some individuals in a population, but not all, whereas lethal alleles kill the entire organism.

What is the primary difference between a recessive allele that causes a genetic disease and one that does not?

If the recessive allele does not cause a disease, the individual is a carrier of the disease, and 50% of the normal protein is enough to accomplish the protein's cellular function.

How do sex-influenced traits differ from sex-limited traits?

Sex-influenced traits are expressed differently in males and females due to autosomal genes, whereas sex-limited traits are observed in only one sex and are determined by sex hormones. Signup and view all the answers

What is the effect of the HEXA gene in individuals with Tay Sachs disease?

The HEXA gene affects the brain and spinal cord due to the accumulation of toxic GM2 ganglioside. Signup and view all the answers

How does incomplete dominance differ from codominance in the expression of phenotypes?

In incomplete dominance, the phenotype of the heterozygote is intermediate between the phenotypes of the homozygotes, whereas in codominance, the phenotype of the heterozygote expresses both alleles. Signup and view all the answers

How do multiple alleles contribute to the expression of traits in an organism?

Multiple alleles, which are different mutations in a gene, can result in hundreds of potential combinations with different phenotypes. Signup and view all the answers

What is the result of a lethal allele in an organism?

The result of a lethal allele is the death of an organism due to the absence of a essential protein required for survival. Signup and view all the answers

What is the role of hormonal factors in the expression of sex-influenced traits in cattle breeds?

In males, the presence of one dominant allele leads to the development of horns, while in females, the expression of the trait can be influenced by hormonal factors such as testosterone. Signup and view all the answers

How does the expression of a heterozygote's phenotype differ from that of a homozygote in a case of codominance?

In a case of codominance, the heterozygote expresses both alleles, whereas a homozygote expresses only one allele. Signup and view all the answers

What is the significance of the 50% threshold for normal protein function in carriers of recessive alleles?

If a carrier has 50% of the normal protein, it is enough to accomplish the protein's cellular function, and the individual will not exhibit the disease. Signup and view all the answers

How do certain circumstances affect the expression of phenotypes, despite Mendel's laws still applying?

Certain circumstances can alter the expression of phenotypes, but Mendel's laws still apply, indicating that the underlying genetic principles remain the same. Signup and view all the answers

What is the term for the proportion of organisms whose phenotype matches their genotype for a given character?

Penetrance Signup and view all the answers

What is the term for the phenomenon where a single gene can result in multiple different phenotypes?

Pleiotropy Signup and view all the answers

What is the term for the phenomenon where a single mutant gene can result in different degrees of expression in different individuals?

Variable expressivity Signup and view all the answers

What is the term for a trait that is environmentally caused but appears to be inherited?

Phenocopy Signup and view all the answers

What is the term for the opposite of pleiotropy, where different genes produce the same phenotype?

Genetic heterogeneity Signup and view all the answers

What is the genetic term for the multiple alleles at a single locus that determines coat color in rabbits?

C gene locus Signup and view all the answers

What is an example of a polygenic disorder that is influenced by a single gene?

Sickle cell disease Signup and view all the answers

What is an example of a condition that can result from a phenocopy, where an environmental factor causes a trait that appears to be inherited?

Melanoma Signup and view all the answers

Study Notes

Lethal Alleles

Lethal alleles can kill an organism due to interference with cell division
Conditional lethal alleles may kill an organism only under certain environmental conditions, such as temperature sensitivity
Semi-lethal alleles may kill some individuals in a population, but not all

Sex-Influenced Traits

Alleles can behave differently in males and females, where an allele is dominant in one sex and recessive in the other
Example: presence of horns in cattle breeds, where the dominant allele leads to horn development in males, but is influenced by hormonal factors in females

Sex-Limited Traits

Traits observed only in one sex, determined by sex hormones
Example: egg production in birds, influenced by oestrogen in females

Multiple Alleles

One gene can have multiple alleles, with different mutations leading to hundreds of potential combinations and phenotypes
Example: Mendelian inheritance patterns following the Law of Segregation and Law of Independent Assortment

Genetic Diseases

Most genetic diseases are caused by mutant alleles, often recessive
Effects of mutant alleles: missing protein, altered function, and changed enzyme activity
Carriers (heterozygotes) can produce 50% of normal protein, enough for cellular function

Incomplete Dominance

Phenotype is intermediate between parent traits
Example: flower colour in snap dragon plants, where red and white parents produce a pink offspring

Codominance

Heterozygote expresses both parental phenotypes
Example: coat colour in certain cattle breed, where the heterozygote expresses both red and white patches

Lethal Alleles and Coat Colour

Lethal alleles can cause death due to absence of essential proteins
Example: coat colour in rabbits, where multiple alleles at the C gene locus determine coat colour

Penetrance and Expressivity

Penetrance: proportion of organisms whose phenotype matches their genotype
Expressivity: genes expressed to different degrees in different organisms, with variable expressivity

Pleiotropy

Single gene (monogenic) disorder with multiple symptoms
Example: sickle cell disease, where a single mutation in the HBB gene leads to multiple symptoms across all body systems

Phenocopies

Environmentally caused traits that appear to be inherited
Example: melanoma skin cancer caused by UV exposure, appearing as a phenocopy

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Description

This quiz covers Mendelian inheritance patterns, including the Law of Segregation and the Law of Independent Assortment, and how they relate to genetic diseases caused by mutant alleles. It also explores the effects of recessive alleles on protein function and the role of carriers in genetic disease transmission.