Week 5

• 1st division nondisjunction violates Mendel's principles
• Linked genes violate Mendel's principles
• Chromatids are A and a for the first chromosome and a for the second chromosome

  
• The chromosomes in C are drawn incorrectly because they do not have similar information when comparing the loci on their chromatids

  
• The X chromosome is 150+ Mb long and the Y chromosome is only about 50 Mb

  
• The X chromosome consists of 1000+ genes and the Y chromosome consists of about 50 genes

  
• The X and Y chromosomes have sequence homology of only 2.7 Mb at the tip of the short arm and 0.3 Mb near the tip of the long arm

  
• 1. linked genes are not present on the X chromosome - a Y-linked trait will only appear in males

  
• An X-linked recessive trait will only appear in females who are homozygous for the recessive allele
• Heterozygous females are carriers and affected males inherit the X-linked allele from their mothers
• Affected males crossed with normal homozygous females have heterozygous daughters that are carriers
• Criss-cross inheritance (specific to the X chromosome): An X chromosome from a male must be transmitted to a female and then that chromosome can be transmitted to a male again

  
• Punnett square showing F1 offspring expectations with independent assortment

  1. 1:1:1 phenotypic ratio expected
• The 1:1:1:1 phenotypic ratio was not observed
• Excess of parental phenotypes


  Phenotypes associated with chromosomes (chromatids) that are nonrecombinant for the w and cv genes

  
• Pedigrees are a useful tool for human genetics

  
• Reasons pedigrees are used for human genetics


  • Humans have fewer offspring
  • Often more data on certain groups or established families
  • Strong interest in traits influenced by multiple genes (polygenic) rather than single gene (monogenic)

  
• Recessive traits


  May skip a generation and carriers play an important role
• Dominant traits


  Can produce affected offspring from one affected parent and affected individuals are more likely to appear in each generation
• For both autosomal recessive or dominant, affected individuals are equally likely to be male or female