Chromosome Theory of Inheritance and Sex-Linkage Flashcards
What does the Chromosomal Theory of Inheritance state?
Individual genes are located at specific positions on chromosomes, and the behavior of chromosomes during meiosis explains Mendelian inheritance.’
How did Boveri and Sutton explain Mendel’s laws?
Chromosomes occur in pairs.
During meiosis, homologous chromosomes separate into gametes, explaining segregation.
Different chromosomes assort independently.
What organism did Morgan use in his experiments?
Fruit flies (Drosophila melanogaster).
What was Morgan’s key finding regarding eye color in fruit flies?
White-eye color is a sex-linked trait carried on the X chromosome.
What is hemizygosity?
A condition in males where they have only one allele for certain X-linked genes.
Why do reciprocal crosses give different results for sex-linked traits?
Because males and females contribute different sex chromosomes (X or Y).
What are the types of sex determination systems?
X-Y system: XX = female, XY = male.
X-O system: XX = female, X = male.
Z-W system: ZW = female, ZZ = male.
Haplo-diploid system: Males are haploid, females are diploid.
What is the inheritance pattern of X-linked recessive traits?
Affected males inherit the allele from their mother.
Females must inherit two recessive alleles to express the trait.
What are the key features of autosomal recessive inheritance?
Affects males and females equally.
Both parents must carry the allele.
~25% of children affected if both parents are carriers.
hat are the key features of sex-linked recessive inheritance?
Typically affects males more than females.
Affected males pass the allele to daughters, not sons.
Traits may skip generations.
What are the key features of autosomal dominant inheritance
Affects males and females equally.
Only one parent needs to carry the allele.
~50% of children affected if one parent has the trait.
What is the phenotypic ratio for Morgan’s second cross involving sex-linked traits?
3:1.
How do sex chromosomes differ from autosomes?
ex chromosomes determine sex and carry genes for other traits, while autosomes do not determine sex.
What is the significance of the Punnett square in sex-linked traits?
It helps predict the inheritance patterns and probabilities of phenotypes based on the parent’s genotypes.
