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Questions and Answers
In the Lygaus mode of sex determination, what type of gametes do males produce?
In the Lygaus mode of sex determination, what type of gametes do males produce?
Which sex determination mode is characterized by females having ZW and males having ZZ chromosomes?
Which sex determination mode is characterized by females having ZW and males having ZZ chromosomes?
What type of trait is cock feathering in chickens categorized as?
What type of trait is cock feathering in chickens categorized as?
What does the SRY gene in the Y chromosome determine?
What does the SRY gene in the Y chromosome determine?
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In which sex determination mode do females produce only one type of gamete?
In which sex determination mode do females produce only one type of gamete?
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Which of the following organisms commonly follows the Lygaus sex determination system?
Which of the following organisms commonly follows the Lygaus sex determination system?
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What is the primary function of the pseudo autosomal region (PAR) on the Y chromosome?
What is the primary function of the pseudo autosomal region (PAR) on the Y chromosome?
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What characteristic defines the Protenor mode of sex determination?
What characteristic defines the Protenor mode of sex determination?
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What is a characteristic of sex-influenced traits?
What is a characteristic of sex-influenced traits?
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Which genotype represents a bearded male goat?
Which genotype represents a bearded male goat?
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What indicates that a trait is X-linked?
What indicates that a trait is X-linked?
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Which of the following is an X-linked recessive disorder?
Which of the following is an X-linked recessive disorder?
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What does hemizygosity refer to?
What does hemizygosity refer to?
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In terms of genotype, what is true for males regarding X-linked traits?
In terms of genotype, what is true for males regarding X-linked traits?
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What is the correct representation of alleles in a male for a specific gene?
What is the correct representation of alleles in a male for a specific gene?
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Which situation represents a sex-limited trait?
Which situation represents a sex-limited trait?
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Study Notes
Sex-determination Systems
- The Lygaus mode defines females as XX (homogametic) producing gamete X, and males as XY (heterogametic) producing X and Y gametes.
- The Abraxas mode identifies females as ZW (heterogametic) producing Z and W gametes, while males are ZZ (homogametic) producing only Z gametes.
- Protenor mode consists of females as XX (homogametic) producing gamete X, and males as XO (heterogametic) producing X or no X gametes.
Modes of Sex Determination
- Protenor System (XX-XO): Females are XX and Males X, seen in grasshoppers and some insects.
- Lygaus System (XX-XY): Females are XX and Males XY, observed in various insects, amphibians, reptiles, and mammals, including humans.
- Abraxas System (ZZ-ZW): Females are ZW and Males ZZ, found in butterflies, birds, and certain reptiles.
Chromosome Y Characteristics
- The Pseudo Autosomal Region (PAR) on chromosome Y is homologous with X and behaves like an autosome.
- Holandric genes, found only on the Y chromosome, are passed from father to son. The SRY gene determines maleness.
- Abraxas mode has hologynic genes (W) transferred from mother to daughter.
Sex-limited and Sex-influenced Traits
- Sex-limited traits are expressed in only one gender (e.g., cock feathering in chickens).
- Sex-influenced traits are expressed in both genders, but dominance differs (e.g., presence of a beard in goats, dominant in males).
X-linked Traits
- Traits linked to the X chromosome are identified through reciprocal crosses; differing results indicate X-linked inheritance.
- Recessive X-linked disorders include color-blindness (daltonism) and hemophilia; vitamin D-resistant rickets is an example of X-linked dominant disorder.
- Crisscross pattern of inheritance shows that recessive traits pass from carrier mothers to sons.
Hemizygosity
- Refers to individuals (e.g., Lygaus males, Abraxas females) who possess only one copy of a gene in a diploid cell.
- In X-linked inheritance, males are hemizygous, carrying only one copy of X-linked genes, affecting genotype and phenotypes differently between genders.
- For polyallelism, the number of gametes and combinations of genotypes differ significantly between males and females.
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Description
Explore the intriguing concepts of sex determination systems covered in Chapter 6 of Genetics & Sexuality. This quiz will test your understanding of Lygaus, Abraxas, and Protenor modes, along with their gametic contributions. Dive in to discover how these modes influence genetic variation among sexes.
