TOPIC 7 - ENERGY & ECOSYSTEMS

• What is the definition of genotype?

  Genetic constitution of an organism
• What is the definition of phenotype?


  The expression of genetic constitution (genotype) and its interaction with the environment
• How do alleles arise?

  Alleles arise by mutation, which are changes in the DNA base sequence
• How many alleles of a gene can be found in diploid organisms?

  2 alleles, as diploid organisms have 2 sets of chromosomes
• What are the different types of alleles?

  Dominant, recessive, and codominant alleles
• What is a dominant allele?

  A dominant allele is always expressed in the phenotype
• What is a recessive allele?

  A recessive allele is only expressed when two copies are present (homozygous recessive)
• What are codominant alleles?

  Codominant alleles are both expressed and contribute to the phenotype if inherited together
• What does homozygous mean?


  Alleles at a specific locus are the same
• What does heterozygous mean?

  Alleles at a specific locus are different
• What do monohybrid and dihybrid crosses show?

  • Monohybrid cross: inheritance of one phenotypic characteristic coded for by a single gene
  • Dihybrid cross: inheritance of two phenotypic characteristics coded for by two different genes
• In a monohybrid cross involving horses, what are the parental genotypes if a non-grey female is crossed with a heterozygous male?

  gg for the non-grey female and Gg for the heterozygous male
• What is the expected ratio of phenotypes in the offspring of a monohybrid cross between a non-grey female and a heterozygous male?

  The expected ratio is 1:1 for grey to non-grey phenotypes
• In the snail species example, what are the parental genotypes for the pink-shelled snails?

  C$P$C$Y$ for both pink-shelled snails
• What is the expected offspring phenotype ratio from a cross between two pink-shelled snails?

  The expected offspring phenotypes are pink-shelled and yellow-shelled snails
• What are the parental genotypes for the ABO blood groups in humans?

  I$A$I$O$ and I$B$I$O$
• What is the expected ratio of phenotypes in the offspring of two heterozygous parents with ABO blood groups?


  The expected ratio is 1:1:1:1 for AB, A, B, and O blood groups
• In a pedigree diagram, how can you determine if a genetic disorder is caused by a dominant allele?

  If two parents without the disorder have a child with the disorder, it indicates a recessive allele

  
• What is the probability that a child from parents with a recessive disorder will be male and have the disorder?


  The probability is $\frac{1}{4}$ or 25%
• What is the process of independent segregation in meiosis?

  • Alleles from one pair of chromosomes can enter a gamete with either allele from another pair
  • This occurs during meiosis when homologous chromosomes separate

  
• What is the expected offspring phenotype ratio from a dihybrid cross involving two unlinked genes?

  The expected ratio is 1:1:1:1 for the four possible phenotypes
• What is a sex-linked gene?

  A gene with a locus on a sex chromosome, typically the X chromosome
• Why are males more likely to express a recessive X-linked allele?

  Males have only one X chromosome, so a recessive allele on that chromosome is always expressed
• In a monohybrid cross involving cattle, what is the probability that the next calf born is hairless?

  The probability is 25% or $\frac{1}{4}$
• What are the expected offspring phenotypes from a cross between a tortoiseshell female cat and a black male?

  The expected offspring phenotypes are tortoiseshell female, black female, ginger male, and black male

  
• What is the expected ratio of phenotypes from a dihybrid cross involving sex linkage in fruit flies?

  The expected ratio is 1:1:1:1 for the four possible phenotypes
• What evidence from a pedigree diagram suggests that a phenotype is recessive and linked to the X chromosome?


  • Mother without the phenotype has a child with the phenotype
  • Indicates the mother is a carrier of the recessive allele

  
• How does autosomal linkage affect inheritance of alleles?

  • Two genes located on the same autosome are inherited together
  • Crossing over can create new combinations of alleles
  • Genes closer together are less likely to be separated by crossing over

  
• What results would indicate that two genes are linked in a cross of fruit flies?

  Results showing a higher number of offspring with parental phenotypes than recombinant phenotypes
• What is the expected outcome of a cross between heterozygous tomato plants for height and leaf type?

  The expected outcome shows a higher number of tall plants with normal leaves
• How can you explain the results of a cross between tomato plants with linked genes?

  The results show that the two genes are linked, as the offspring ratios deviate from expected Mendelian ratios
• What is autosomal linkage?

  It is when no crossing over occurs and genes are close together on the same chromosome.
• What gametes are produced due to autosomal linkage?

  Only GL and gl gametes are produced, with no Gl and gL gametes.
• What offspring are not produced due to autosomal linkage?

  No Ggll and ggLl offspring are produced.
• What is the relationship between the genes for height and leaf type in tomato plants?

  • Genes for height and leaf type are on the same homologous pair of chromosomes.
  • Allele T (tall) is dominant to allele t (dwarf).
  • Allele M (normal leaves) is dominant to allele m (mottled leaves).

  
• How many offspring were tall plants with normal leaves in the study?

  1850 offspring were tall plants with normal leaves.
• How many offspring were dwarf plants with mottled leaves in the study?

  579 offspring were dwarf plants with mottled leaves.
• What does it indicate if genes are linked in terms of gamete production?

  It indicates that mainly TM and tm gametes are produced.
• What happens when crossing over occurs in linked genes?

  Fewer Tm and tM gametes are produced, leading to fewer tall, mottled and dwarf, normal offspring.
• What is the expected phenotypic ratio if the genes for height and leaf type were on different homologous pairs of chromosomes?

  The expected ratio is 9:3:3:1.