genetic inheritance

Question 1

Mendel’s 3 laws of inheritance

Answer 1

1. segregation, 2 alleles per trait per individual, segregate during meiosis so gamete has 1 allele
2. independent assortment, alleles for separate traits inherited independently
3. dominance, recessive alleles are completely masked by dominant allele in heterozygous state

Question 2

exceptions to mendel’s 1st law, segregation

Answer 2

• clonal reproduction
• haplo-diploid organisms
• sex chromosomes

Question 3

exceptions to mendel’s 2nd law, independent assortment

Answer 3

• clonal reproduction
• chromosomal linkage, crossing over less likely to split up genes on same chromosome so more likely to be inherited together

Question 4

exceptions to mendel’s 3rd law, dominance

Answer 4

• incomplete dominance, phenotype of heterozygote is intermediate between the two homozygotes
• codominance, phenotype of heterozygote contains traits of both alleles

Question 5

epistasis

Answer 5

one gene modifies or controls the expression of another gene, can be dominant or recessive

Question 6

dominant epistasis

Answer 6

• dominant allele masks all alleles at other genes, recessive alleles have no effect
• e.g. white coat (and blue eyes and deafness) gene in cats

Question 7

recessive epistasis

Answer 7

• recessive allele masks other alleles if homozygous
• e.g. white coat genes in mice

Question 8

mendelian traits

Answer 8

trait controlled by one gene e.g. dry vs sticky earwax

Question 9

quantitative traits

Answer 9

• trait controlled by many genes e.g. height
• additive effect, as number of genes contributing to a trait increase, number of phenotypes increase and distribution of trait values approaches normal distribution