HL 1 Biology

4.3c Genetics

150-3; 156

 Hemophilia in Queen Victoria’s family (p.153)

1) If the male has the allele, then they will be affected since the condition is resulted during the process of sex.

2) The female requires copies of the allele from a carrier mother and an affected father, which is known to be rare.

3) The males are the only ones affected since the combination of a carrier female and unaffected male can produce an affected male. The inheritance of the alleles looks like it is from the mother side.

4)  Alexandria seems to be the carrier and yet Nicolas is not affected. All the daughters can be the carriers and they may not have the copies of the allele or have one copy.

5) Looking at the pedigree, the normal male is XHY. Yet there is a 50% probability it may be XhY if the pedigree is not presented.

Chapter 12 Questions (p.156)

1 a) Genotype: is the alleles possessed by an organism. Phenotype: the characteristics of an organism

b) Dominant: an allele that has the same effect on the phenotype whether it is present in the homozygous/heterozygous state. Recessive:  an allele which only has an effect on the phenotype when present in the homozygous state

c) Homozygous: having 2 identical alleles of a gene.  Heterozygous: having 2 different alleles of a gene

d) Gene: a heritable factor that controls a specific characteristic. Genomethe whole of the genetic information of an organism

e) Haploid: having a single set of unpaired chromosomes. Diploid: having 2 complete sets of chromsomes (one from each parent)

2 a) L, is the allele for the four-leaf clover and l, is the allele for the three-leaf clover. Genotype of F1 plants is: Ll

b i) Expected ratio of genotypes and phenotypes in the F2 generation; 3:1 of four-leaf to the three-leaf clover Screen shot 2013-02-07 at 10.28.24 AM

ii) This is not the expected ratio since not many clovers have four-leaves. The wild ratio is because of the natural selection and also the frequencies of the allele in the gene.

c) The three-leaved clover will produce more three-eaved clovers when they are crossed together. The homozygous of the four-leaf clover can be seen when crossed with the three leaved clover. Test-crossing the four leaved clovers, that only produce flour leaved offsprings when crossed with three leaved plants = are homozygous.

3 a) Genotypes of each person: A = IAi

B =IBi or some are IB IB

O= ii


b) 25% of A, B, AB, or O.

c i) 100% group O

ii) 25% in group AB and B, though 50% in group A

4 a)  B is dominant: b is recessive and CR is co-dominant

b) Homozygous: A  and Heterozygous: B

c) Chromosomes are homologous because they have the same genes in similar sequences although they are different alleles.

d) B and b are shown as different alleles in the same gene since they have same positioning and same letters are used to denote them as well as the locus is presented on the chromosomes.

5 a) The son inherited hemophilia from his mother who is a carrier of the X allele and an allele from his father who is a non-carrier.

b) Since the son is a non-hemophiliac, there is no chance of his children inheriting hemophilia unless his wife is a carrier. If the wife consists of the X allele, there is a 50% chance the son could inherit hemophilia but not for the daughters.

c) Possible social effects for the family of the hemophilia and AIDS include guilt and anxiety feelings. People who’ve inherited hemophilia can be ill and will have to visit hospitals several times. Parents can feel guilt and anxiety from knowing the fact they passed on the hemophilia to their own child. AIDS can cause an effect on social relations of working and become unemployed.

6 a)  There could be a dark wing from the dominant allele and a light wing from the recessive allele.

b) There is a 3:1 ratio between the dark and light.  


d) Males have 2 X chromosomes and the females consist of one X and Y chromosome.

e) ALl the female offfspring have light wing and all the male offspring have dark wings when the XDY is crossed with the XdXd.



One thought on “4.3c Genetics

  1. IB 1-7

    Grade 6 A consistent and thorough understanding of the required knowledge and skills, and the ability to apply them in a wide variety of situations.

    Data-based questions: hemophilia in Queen
    Victoria’s family
    page 153
    1 The condition is sex-linked
    if a male possesses the allele
    then they will be affected.
    2 The female would need two copies of the allele
    which would require a carrier mother and an affected father.
    This is a rare combination.
    3 Only males are affected
    inheritance in males appears to be from maternal line
    Carrier female and unaffected male produces affected male.
    4 Alexandria is a carrier and Nicholas is unaffected.
    Daughters could be carriers/ XHXh
    or possess nocopies of the allele / XHXH
    5 The normal male symbol in the pedigree suggests that they are XHY,
    though without reference to the pedigree there would a 50% chance that they could be XhY.

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