7a&b - Patterns & Principles of Heredity

Question 1

law of segregation

Question 1

how are traits transmitted from one generation to next?

Question 2

law of independent assortment

Question 3

particulate theory of inheritance

Answer 3

• characters are distinct & hereditary determinants (genes) are particulate in nature
• each adult has 2 genes for each character; diff forms of genes called ‘alleles’
• members of gene pair segregate equally into gametes
• fusion of gametes at fertilisation restores pair of genes & is random
• diff genes assort independently in gametes

Question 4

gene

Answer 4

• basic unit of biological info
• specific segment of DNA that encodes a protein

Question 5

allele

Answer 5

alternate forms of gene

Question 6

genotype

Answer 6

alleles at a locus

Question 7

phenotype

Answer 7

observable (eg color) characteristics

Question 8

homozygote

Answer 8

identical (YY) alleles at a locus

Question 9

heterozygote

Answer 9

diff (Yy) alleles at a locus

Question 10

incomplete dominance

Answer 10

heterozygotes show intermediate
phenotype

eg. red x white = pink!

Question 11

co-dominance

Answer 11

heterozygotes show phenotype of both alleles

Question 12

example of co-dominance?

Answer 12

human MN blood groups -> M, N & MN

Question 13

PreP Pre-exposure Prophylaxis

Answer 13

(medicine that ↓ chances of getting HIV from sex / injection drug use)

• daily pill to protect against HIV infection
• 90% effective
• targeted at gay men having unprotected sex
• cost: £5,000 a year -> (lifetime cost of HIV treatment is £300,000)
• anti-retroviral drug:
  -> same used to cure HIV infection
  -> prevents rapid HIV replication when it enters body
  -> allows immune system to deal with HIV infection before it takes hold

Question 14

Pleiotropy

Answer 14

1 gene may contribute to more than 1 trait

Question 15

pleiotropy example in humans

Answer 15

cilia (in nasal epithelium) & flagella (in sperm tail)

• same motor drives cilia & flagella
• so if you have defect in flagella function (causing sterility), also have respiratory problems (failure to clear airways) from cilia

Question 16

why might you only have a 2:1 ratio in punnet square instead of 1:2:1?

Answer 16

can have lethal combos

lethal alleles can cause skewed phenotypic ratios (missing from progeny)

Question 17

coat colour in mammals is determined by at least 5
major genes…

Answer 17

• A gene - determines distribution of pigment in hair
  -> ‘A’ allele = agouti
  -> ‘a’ allele = solid
• B gene - determines colour of pigment in hair
  -> ‘B’ allele = black
  -> ‘b’ allele = brown
• C gene - permits colour expression
  -> ‘C’ allele = colour is expressed
  -> ‘c’ allele = no colour
• D gene - controls intensity of pigment specified by other genes
  -> ‘D’ allele = full expression
  -> ‘d’ allele = dilute
• S gene - controls distribution of pigment
  -> ‘S’ allele = solid colour
  -> ‘s’ allele = spotted (piebald)

Question 18

epistasis

Answer 18

gene interaction where effects of allele at 1 gene hide effects of alleles at another gene

eg. red & white onions

Question 19

suggest why there could be a phenotypic ratio of 9:4:3 in mammal coat colour

Answer 19

epistasis

albino masks a category

Question 20

Penetrance

Answer 20

• measures % of individuals with given genotype…
• who exhibit the phenotype associated with the genotype

Question 21

Expressivity

Answer 21

measures extent to which a given genotype is expressed at the phenotypic level