HL 1 Biology

4.3b Genetics

AA-CC: 146-9

<<Test Crosses>>

Homozygous: having two identical alleles of a gene

Heterozygous: having two different alleles of a gene

  • organism consists one dominant allele and the other being recessive
  • dominant: allele that has the same effect on the phenotype wheater it is present in the homozygous or the heterozygous state
  • recessive: an allele that only has an effect on the phenotype when it is present in the homozygous state

Test cross: testing a suspected heterozygote by crossing it with a known homozygous recessive

<<Inheritance of ABO blood groups>>

Co-dominant alleles: pairs of alleles that both affect the phenotype when in a heterozygote

  • e.g. flower color of Mirabilis jalapa
  • pink-flowered plant crossed

ABO blood group system = an example of co-dominance

  • glycoprotein
  • 2 alleles being co-dominant and the other allele being recessive is important

Gene mutation: a change to the base sequence of a gene; a random change

  • mutations in cells can develop into gametes and be passed on to offsprings and cause genetic diseases


Deducing genotypes form pedigree charts (p.146)

1) The condition is due to a recessive allele because unaffected parents in the very first generation have produced children that are affected. Since the previous generation did not have the phenotype, the condition can be stated to be due to an recessive allele. 

2 a) Homozygous recessive:  100%

b) Heterozygous: 0%

c) Homozygous dominant: 0%

3 a) Dd because the female mother is likely to have genotypes of dd

b) DD since it is a rare condition. Also, the person is marrying to a person with a history of the disease going through the families generations.

4) Generation II, 4 and 5 as well as Generation II, 7 and 8. These are because they are crossed with a known homozygous recessive.

The two-spot ladybird (p.147)

1) The typica and annulata both consist of the colors red and black. Yet, the annulata has a more unique patter of the black dots where as the typica consist of perfect black round dots on its back.

2) In cases of typica parents mating and producing a typica offspring as well as the parents annulata producing annulata offspring, they both breed purely in which each parent does not breed with a object with a different species.

3) The F1 hybrid offspring consists of more black spots or pigmentation compared to those offsprings typica and annulata. The pattern of the black pigmentation is also different, yet there are some with the similar patterns of the black spots as the original parents pattern.

4 a)  The genetic diagram with the pattern of inheritance show the pattern of inheritance

b)The expected ratio of phenotypes could be 3:1

Distribution of ABO blood groups (p.148)

1 a) Northern India: 25-30%

b) Japan: 15-20%

c) North America: 5-10%

2) Frequency of the allele i in South America: 5-10% frequency and 5% looking at data thus: 85%~90%. 5+ 5 or 5+10 – 100.

3) Gypsies in Europe have a much higher frequency of IB than other indigenous groups in Europe because these gypsies could have transferred from a more higher frequency are such as Northern India. Also, this area of Europe does not have much easy access to the general European population.

4) The IB frequency could decrease as the frequency of South America is lower than the 10%~20%.

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