Modified Mendelian Ratios

Question 1

Probability and rules

Answer 1

• the ratio of predicted occurrence of a particular outcome or event divided by the total number or possibilities/trials
  1. product rule- The probability of 2 independent events occurring together is the product of the probabilities of either event occurring alone
  2. sum rule- The probability that mutually exclusive events will occur together is equal to the sum of their individual probabilities
  Corollary to sum rule- all the mutually exclusive probabilities must add up to 1

Question 2

binomial expansion to find possible outcomes

Answer 2

• use Pascal’s triangle

Question 3

Incomplete dominance

Answer 3

• also called partial dominance or absent
• dilution
• ex. red and white flower–> intermediate phenotype is 1 dominant and 1 recessive–> pink flower
• ratio is 1:2:1

Question 4

co-dominance

Answer 4

• multiple alleles expressed equally

- ex. blood type- both A and B genes expressing fully (not diluted)

Question 5

multiple alleles

Answer 5

• more than 1 allele

- Blood types, A, B, and O

Question 6

polygenic

Answer 6

• many genes (don’t know how many)
• shows a normal curve
• contributing and noncontributing allele
• ex. height- over 100 alleles for height, curve has shifted over the years (nutrition, other factors)

Question 7

heritability

Answer 7

• based on total variability and the environment

Question 8

sex-influenced

Answer 8

• on autosomes
• Influenced by sex (testosterone) not sex linked (on chromosomes)
• expression in males different than in females
• ex. pattern baldness

Question 9

sex limited

Answer 9

• genes only expressed in 1 sex
• (+) indicates dominant form of gene - sometimes + is the ”wild type” form of gene (more common in nature)
• ex. chickens, females always hen-feathered, males are cock feathered when h/h (recessive)

Question 10

interaction of genes

Answer 10

• 2 genes interact together in expressions so give a phenotype that you wouldn’t have without the two genes
• Ex. chicken comb shape
• -2 genes that affect comb shape (R and P)
• -Recessive for both–> single comb
• -Dominant R–> get rose comb
• -Dominant P–> pea comb
• -Dominant in both R and P–> walnut comb
• • ratio is 9:3:3:1
    ex. snake color pattern

Question 11

epistasis

Answer 11

• Standing upon- Expression of 1 gene interferes with the expression of another
• ratio 9:6:1
• ex. squash shape

Question 12

temperature effects

Answer 12

• Pigment genes- affected by temperature
• ex. Siamese cats- dark pigment is present because it is cooler in extremities that the core of the cat
• -> Changes throughout life- as they grow hair

Question 13

environmental factors

Answer 13

• temperature
• drugs ex. thalidomide- sedative for morning sickness, drug interfered in step involved in signaling and development–> limb defects (Phocomelia)
• thalidomide can be used to fight leprosy

Question 14

cystic fibrosis

Answer 14

• autosomal homozygous recessive
• affects 1/2000 caucasian
• affects gene coding for Chloride ion channel functioning
• -> affects narrow passages (lumen), sweat glands, digestive area, lungs, pancreas, liver
• -> Affects organs by causing accumulation of thick mucus (instead of watery mucus)
• affected die young
• NOW- can supplement digestive function with enzymes