17 Questions
What does high concordance in identical twins and low concordance in fraternal twins suggest about a trait?
Strong hereditary element
How do alleles segregate between gametes during meiosis?
Equally
Which of the following is NOT a method classical geneticists use?
Crossing over
Sex-linked genes deviate from standard Mendelian inheritance because:
They follow a different pattern of inheritance
What influences the phenotypes of sex-linked traits?
Genes, chromosomes, and environment
What determines the male/female phenotype (sex) according to the module summary?
Genes, chromosomes, or environment
In X-Linked Dominant inheritance, how many copies of the disease allele are required for an individual to express the phenotype?
One copy
How does consanguinity increase the risk of inheriting autosomal recessive diseases?
By increasing the chances of offspring inheriting two copies of a disease allele
In X-Linked Recessive inheritance, what is the genotype of affected individuals?
Homozygous recessive
What is a characteristic deviation from Mendel's rules for loci on the sex chromosomes?
Sex linkage
For X-Linked genes, what is a well-studied example mentioned in the text?
The white gene in Drosophila melanogaster
In sex-linked traits, what causes most loci on the typical X chromosome to be absent on the Y chromosome during meiosis?
Non-homologous pairing
In X-linked dominant diseases, if a female is affected, what can be said about her sons?
They will all be unaffected.
Which of the following is an example of an X-linked recessive disease?
Colorblindness
For a carrier female of an X-linked recessive disease, what is the chance that her daughters will inherit the disease allele?
50%
In deviations from Mendel's rules, what can be said about phenotypes and genotypes?
Phenotypes can sometimes differ from what is expected based on genotypes.
What is the likelihood that an affected male with an X-linked recessive disease will transmit the disease allele to his sons?
0%
Study Notes
Twin Studies
- High concordance in identical twins and low concordance in fraternal twins indicates a strong hereditary element for a trait.
- Equal concordance and discordance ratios between identical and fraternal twins suggest less hereditary influence and more environmental influence on a trait.
Classical Genetics
- A diploid can have up to two different alleles at a single locus.
- Alleles segregate equally between gametes during meiosis.
- Phenotype depends on alleles, their dominance relationships, and interactions with the environment and other factors.
Sex-Linked Genes
- Sex-linked genes are an exception to standard Mendelian inheritance.
- Phenotypes are influenced by the type of sex chromosome system and dosage compensation system found in the species.
- Male/female phenotype (sex) can be determined by chromosomes, genes, or the environment.
Autosomal Recessive
- Only one copy of a disease allele is necessary for an individual to be susceptible to expressing the phenotype.
- There is a 50% chance the offspring will inherit the disease allele.
- Affected individuals have a homozygous recessive genotype, while heterozygotes (carriers) have a wild-type allele that masks the mutant allele.
- Parents of an affected individual are not affected but are gene carriers.
- Marriage between relatives increases the risk of inheriting autosomal recessive diseases.
Pedigree Analysis
- A pedigree shows a family tree with respect to a given trait.
- Pedigree analysis reveals patterns of inheritance.
Sex-Linkage
- Loci on autosomes follow the normal Mendelian pattern of inheritance.
- Loci on sex chromosomes follow a sex-linked pattern of inheritance.
- The X chromosome has most loci absent from the Y chromosome, despite acting as a homologous pair during meiosis.
X-Linked Genes
- The white gene on the X chromosome of Drosophila melanogaster is a well-studied sex-linked gene.
- X-linked dominant diseases include Rett syndrome, Double-cortex syndrome, and Incontentia pigmenti type 1.
- X-linked recessive diseases include Duchenne muscular dystrophy, Colorblindness, Hemophilia A, and G-6-P-D.
X-Linked Recessive
- Two copies of a disease allele on the X chromosome are required for a female to be affected.
- Any male with one copy of an X-linked recessive disease allele is affected.
- Females are usually carriers because they only have one copy of the disease allele.
- For a carrier female, with each pregnancy, there is a 50% chance her sons will inherit the disease allele and a 50% chance her daughters will be carriers.
- Affected males transmit the disease allele to all of their daughters, who are then carriers, but to none of their sons.
Test your knowledge on autosomal recessive inheritance, where having only one copy of a disease allele leads to susceptibility. Understand the 50% chance of inheriting the disease allele and how affected individuals possess a homozygous recessive genotype.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
