The Principles of Inheritance

Question 1

TRAITS AND GENES

Answer 1

• A trait is an inherited characteristic of an individual (many traits are each the result of a single gene)
• Since a trait may have varieties (e.g. curly vs straight hair) it must be possible for their to be carriers of the same gene (this individual genes can have multiple forms; alleles)
• Alleles differ in DNA sequence in small ways
• Potentially this results in proteins that differ somewhat in amino acid sequence and that may lead to differences in the activity of the proteins

Question 2

INHERITANCE OF TRAITS

Answer 2

• So the basis of differences between individuals is due to there being alleles
• The genotype of the offspring is made up of all pairs of alleles inherited from its parents
• The set of genes for any organism are present in strands of DNA called chromosomes
• Thus: the genome of each organisms comprises pairs of chromosomes
• Each particular gene for a particular species is always in the same location on the same chromosome in each member of the species

Question 3

PRINCIPLES OF SEGREGATION

Answer 3

• Individuals carry pairs of alleles that influence particular traits
• The alleles segregate during the formation of gametes (sperm and ova) such that any individual gamete contains only one of each pair of alleles
• Gametes are formed through a special form of cell division called meiosis

Question 4

MEIOSIS

Answer 4

• Meiosis is unique to the production of sperm and ova

- The parent cell has pairs of chromosomes just like all the other cells in the body

Question 5

SIMPLIFIED MODEL LOOKING AT THE FATE OF JUST ONE PAIR OF CHROMOSOMES

Answer 5

• The first thing that happens is an exact duplicate of each chromosome is made
• The parent cell undergoes cell division to produce up to 4 gametes
• Each gamete will only have one chromosome from each pair

Question 6

ALLELES AND EXPRESSION

Answer 6

If someone is homozygous for a particular gene

• The alleles of the gene are the same
• The cells of that person will produce one version of the protein encoded by the gene

If someone is heterozygous for a particular gene

• The alleles are not identical
• The cell;s of that person may produce 2 versions of the protein encoded by the gene
• But this is not always the case
• The genotype of a person is made up all of pairs of alleles inherited from its parents
• The phenotype of a person is the collection of traits of that person
• These are the result interactions between the alleles

Question 7

PATTERNS OF INTERACTION BETWEEN ALLELES: CO-DOMINANCE

Answer 7

In case of co-dominance, in the heterozygote, both alleles are expressed equally

Question 8

PATTERNS OF INTERACTION BETWEEN ALLELES: INCOMPLETE DOMINANCE

Answer 8

In incomplete dominance, the phenotype of heterozygote lies between each of the homozygotes

Question 9

PEDIGREES: AUTOSOMAL AND X-LINKED

Answer 9

Autosomal chromosomes are chromosomes 1-22

Sex chromosomes are the 23rd pair

Question 10

AUTOSOMAL DOMINANT INHERITANCE

Answer 10

• Both genders exhibit the trait in approximately equal numbers
• Disease should not skip generations

Question 11

X-LINKED RECESSIVE INHERITANCE

Answer 11

• Trait more frequently seen in males
• Not transmitted from father to son
• Disease can skip generations
• Female carriers will transmit it to approximately half their sons

Question 12

AUTOSOMAL RECESSIVE INHERITANCE

Answer 12

• Both genders exhibit the trait in approximately equal numbers
• Disease may skip a generation
• If carriers mate: approximately one quarter of offspring will be affected