Key Terms

• What is essential for cell survival?

  DNA contained within chromosomes
• What does every chromosome consist of?

  A long DNA molecule coding for proteins
• What is a gene?

  A length of DNA coding for a protein
• What is the position of a gene on a chromosome called?

  Locus
• What are different forms of a gene called?

  Alleles
• How do different alleles of a gene differ?

  They have slightly different nucleotide sequences
• What coat colour does allele B produce in horses?

  Black coat

  
• What coat colour does allele b produce in horses?

  Chestnut coat

  
• How do chromosomes occur in eukaryotic cells?

  In homologous pairs
• What does having two copies of every gene allow for?

  Diverse allele combinations within an individual
• What does the genotype of an organism refer to?

  The alleles of a gene possessed by that individual
• How can different alleles be represented?

  By letters
• What is it called when two allele copies are identical in an individual?

  Homozygous
• What is it called when two allele copies are different in an individual?

  Heterozygous
• How does genotype affect phenotype?

  The genotype influences observable characteristics
• What is the genotype of a horse with two black coat alleles?

  AA and is homozygous
• What is the phenotype of a horse with genotype AA?

  Black coat
• What is the genotype of a horse with one black coat allele and one chestnut coat allele?

  Aa and is heterozygous

  
• How do dominant alleles affect phenotype?

  They are always expressed in the phenotype
• How do recessive alleles affect phenotype?

  They are expressed only if no dominant allele is present
• What genotype results in a black coat if allele A is dominant?

  AA or Aa

  
• What genotype results in a chestnut coat if allele a is recessive?

  aa

  
• What is codominance?

  Both alleles are expressed in the phenotype
• How are alleles represented in codominance?

  By different superscript letters
• What genotype results in blood type AB?

  I$A$I$B$
• What genotype results in blood type O?

  I$O$I$O$
• What are the offspring of the F1 generation called?

  F2 generation
• What is a test cross used for?

  To deduce the genotype of an unknown individual
• How is a test cross performed?

  Crossing with a recessive phenotype individual
• What are the two types of linkage in genetics?

  Sex linkage and autosomal linkage
• What are the two sex chromosomes?

  X and Y
• How do women and men differ in sex chromosomes?

  Women have XX, men have XY
• What are sex-linked genes?

  Genes found on sex chromosomes
• How are sex-linked genes represented in genotype?

  By writing alleles as superscript next to sex chromosome
• What is autosomal linkage?

  Genes on the same chromosome do not assort independently
• What should be noted when referring to different alleles?

  Use capitals for dominant and lowercase for recessive
• What letters should be used to represent alleles?

  Letters that are easy to distinguish