1. Biology 12

2. Definitions Allele - alternative form of a gene
Chromosome – chunk of DNA
DNA – the genetic information in a nucleus
Gene – section of chromosome that controls one characteristic
Dominant – the allele that is expressed in a heterozygote
Co-dominant – both alleles are expressed in a heterozygote
Recessive – the allele that is not expressed (hidden) in the heterozygote
Autosomal – carried on one of the non-sex chromosomes (autosomes)
Sex-linked – carried on one of the sex chromosomes (X or Y)
Multiple alleles – more than 2 alleles exist for 1 characteristic
Genotype – alleles present in an organism
Phenotype – alleles expressed in an organism (ie its appearance)
Heterozygous – has 2 different alleles for a characteristic
Homozygous – has 2 alleles the same for a characteristic
Hybrid – has 2 different alleles for a characteristic
Pure-breeding – has 2 alleles the same for a characteristic
Hemizygous – has only 1 allele for a characteristic eg males with sex linked condition

3. Genetics problems 1
Tabby is dominant to black coat colour in cats. Predict the genotype and phenotype ratios expected from a cross between a hybrid tabby and a black cat.
Tongue rolling is dominant to non-tongue rolling in humans. Predict the genotype and phenotype ratios expected from a cross between a heterozygous tongue roller and a non tongue roller.
Short hair is dominant to long hair colour in cats. Predict the genotype and phenotype ratios expected from a cross between a hybrid short-haired cat and a long hair cat.
Astigmatism is dominant to normal vision in humans. Predict the genotype and phenotype ratios expected from a cross between a person heterozygous for astigmatism and a normally sighted person.

4. Genetics problems 1 T = tabby t = black Cross is Tt x tt
Tabby is dominant to black coat colour in cats. Predict the genotype and phenotype ratios expected from a cross between a hybrid tabby and a black cat.
Short hair is dominant to long hair colour in cats. Predict the genotype and phenotype ratios expected from a cross between a hybrid short-haired cat and a long hair cat.
T = tabby t = black
Cross is Tt x tt
Genotypes ½ Tt, ½ tt
Phenotypes ½ tabby, ½ black t t
H = short h = long
Cross is Hh x hh
Genotypes ½ Hh, ½ hh
Phenotypes ½ short, ½ long h h T Tt tt H Hh hh t Tt h Hh hh tt
Tongue rolling is dominant to non-tongue rolling in humans. Predict the genotype and phenotype ratios expected from a cross between a heterozygous tongue roller and a non tongue roller.
Astigmatism is dominant to normal vision in humans. Predict the genotype and phenotype ratios expected from a cross between a person heterozygous for astigmatism and a normally sighted person.
T = tongue roller
t = non tongue roller
Cross is Tt x tt
Genotypes ½ Tt, ½ tt
Phenotypes ½ tongue roller, ½ non tongue roller
A = astigmatism
a= normal vision
Cross is Aa x aa
Genotypes ½ Aa, ½ aa
Phenotypes ½ astigmatism, ½ normal t t a a T Tt tt A Aa aa T Tt tt a Aa aa

5. Genetics problems 2
Red flower colour is co-dominant with white flower colour in snap dragons, with the heterozygote showing pink flowers
Predict the genotypes and phenotypes expected from crossing a white flowered plant and a red flowered plant
Predict the genotypes and phenotypes expected from crossing a pink flowered plant and a white flowered plant
Predict the genotypes and phenotypes expected from crossing a pink flowered plant and a red flowered plant
Predict the genotypes and phenotypes expected from crossing 2 pink flowered plants

6. Genetics problems 2
Red flower colour is co-dominant with white flower colour in snap dragons, with the heterozygote showing pink flowers
Predict the genotypes and phenotypes expected from crossing a white flowered plant and a red flowered plant
Predict the genotypes and phenotypes expected from crossing a pink flowered plant and a red flowered plant
FRFR = red, FWFW = white, FR FW = pink
FRFR x FW FR FR FW
FWFW x FRFR  all FWFR pink FR
FRFR
FRFW
½ FRFR = red, ½ FRFW = pink FR
FRFR
FRFW
Predict the genotypes and phenotypes expected from crossing a pink flowered plant and a white flowered plant
Predict the genotypes and phenotypes expected from crossing 2 pink flowered plants
FWFW x FW FR FR FW FR FW FW
FRFW
FWFW
FRFW x FR FW FR
FRFR
FRFW
FWFW FW
FRFW
FRFW
FWFW FW
½ FRFR = red, ½ FRFW = pink
1 FRFR = red : 2 FR FW = pink : 1 FWFW = white

7. Genetics problems 3
Haemophilia is a disease carried as a sex-linked recessive trait.
What genotypes and phenotypes are expected if a haemophiliac male marries a homozygous normal female?
What genotypes and phenotypes are expected if a haemophiliac male marries a heterozygous female?
What genotypes and phenotypes are expected if a normal male marries a heterozygous female?
What is the probability of having a son with haemophilia, if a haemophiliac male marries a heterozygous female?

8. Genetics problems 3
Haemophilia is a disease carried as a sex-linked recessive trait.
XHXH = normal female, XHXh = carrier female, XhXh = haemophiliac female
XHY = normal male, XhY = haemophiliac male
What genotypes and phenotypes are expected if a normal male marries a heterozygous female?
What genotypes and phenotypes are expected if a haemophiliac male marries a homozygous normal female?
XHXH x XhY
XHXh x XHY XH XH XH Xh
All females carriers XHXh
all males normal XHY Xh
XHXh
XHXh XH
XHXH
XHXh Y
XHY
XHY Y
XHY
XhY
What genotypes and phenotypes are expected if a haemophiliac male marries a heterozygous female?
What is the probability of having a son with haemophilia, if a haemophiliac male marries a heterozygous female? XH Xh XH Xh
XHXh x XhY
XHXh x XhY Xh
XHXh
XhXh Xh
XHXh
XhXh
Probability is 1/4 Y Y
XHY
XhY
XHY
XhY
½ females are XHXh = carrier, ½ females are XhXh = haemophiliac
½ males are XHY = normal, ½ males are XhY = haemophiliac

9. Pedigrees
These are diagrams that show the inheritance of characteristics within families
They allow us to determine the pattern of inheritance and predict characteristics of future offspring
Conventions include

10. Autosomal dominant recessive crosses
Pedigrees will show 2 phenotypes.
Crossing a homozygous dominant with a homozygous recessive leads to heterozygous offspring with the dominant trait
Crossing 2 heterozygous individuals leads to offspring which could show either trait bb BB Bb Bb Bb B_ B_ bb B_

11. Autosomal co-dominant crosses
Pedigrees will show 3 phenotypes.
Crossing a homozygous dominant with a homozygous recessive leads to heterozygous offspring with the intermediate trait
Crossing 2 heterozygous individuals leads to offspring which could show any of the three phenotypes
SBSB
SWSW
SBSW
SBSW
SBSB
SBSW
SWSW
SBSW

12. Determining patterns of inheritance 1
Autosomal recessive
Heterozygotes don’t show trait so it may skip generations
If both parents have it, all offspring will have it
Parents don’t have to have it
Autosomal dominant
Heterozygotes do show trait so it can’t skip generations
Even if both parents have it, offspring don’t have to show it
At least one parent must have it
Autosomal co-dominant
3 phenotypes are present

13. Sex linked inheritance
Males and females have different chromosomes
Males can only show 2 phenotypes (ie males can not be carriers)
Females can show 3 phenotypes (if codominant) or 2 phenotypes (if dominant recessive, with a carrier)
Males and females will show different patterns of inheritance

14. Determining patterns of inheritance 2
In sex-linkage mothers pass to sons, fathers pass to daughters
Sex-linked recessive
Mainly in males
Females can only have it if father has it and mother is at least a carrier
Affected females pass it to all their sons
Sex-linked dominant
Fathers pass to all daughters
Mothers pass to half their sons
Sex-linked co-dominant
Only females can show intermediate trait

15. Reading pedigrees Autosomal recessive Autosomal dominant
Sex linked recessive
Autosomal recessive

16. Pedigree problem 1 a) How many males are there?
b) How many females are there?
c) How many males have long fur?
d) How many females have short fur?
e) What type of inheritance is this?
f) Write the most likely genotype of each individual on the pedigree.
g) Which individuals are definitely homozygous?
h) Which individuals are definitely heterozygous?
i) How could you confirm the genotypes of the short haired cats in the fourth generation?
j) What offspring would you expect from a cross of III1 and II6?

17. Pedigree problem 1 L = short fur l = long fur ll ll LL LL ll ll ll ll
a) How many males are there? 9
b) How many females are there? 9
c) How many males have long fur? 4
d) How many females have short fur? 3
e) What type of inheritance is this? Autosomal recessive
f) Write the most likely genotype of each individual on the pedigree.
g) Which individuals are definitely homozygous? Shaded ones
h) Which individuals are definitely heterozygous? Unshaded ones with shaded children and/or a shaded parent
i) How could you confirm the genotypes of the short haired cats in the fourth generation? Test cross (breed to long haired cat)
j) What offspring would you expect from a cross of III1 and II6? Ll x ll = 50% Ll (short hair) 50% ll (long hair) Ll l ll

18. Pedigree problem 2 a. What is the pattern of inheritance is this?
b. Write the genotype for each individual.
c. What offspring would you expect if you mated individual III 1 to:
i) III 2?
ii) III 3?
iii) I 1?

19. Pedigree problem 2
CSCS = spotted
CDCD = dark
CDCS = sable
CSCS
CDCD CS CD
CDCS
CDCS
CDCS
CDCD CD
CDCD
CDCS
CDCS
CDCD
CDCSD
CDCD
CDCD CD
CDCS
CSCS
a. What is the pattern of inheritance is this? codominance
b. Write the genotype for each individual.
c. What offspring would you expect if you mated individual III 1 to:
i) III 2? x =
ii) III 3? x = ½ : ½
iii) I 1? x =
CDCS
CDCD
CSCS
CDCD
CDCS
CDCD
CDCS
CDCD
CSCS
CDCS

20. Pedigree problem 3
Is this trait dominant or recessive? Give reasons to justify your answer.
Is this trait autosomal or sex-linked? Give reasons to justify your answer.
Which individuals are definitely homozygous?
Which individuals are definitely heterozygous?
What is the probability of individuals II2 and II8 having white coated offspring? Show all working.

21. Pedigree problem 3 B = black b = white
Is this trait dominant or recessive? Give reasons to justify your answer. recessive
Is this trait autosomal or sex-linked? Give reasons to justify your answer. autosomal
Which individuals are definitely homozygous? Shaded ones
Which individuals are definitely heterozygous? Unshaded ones with shaded children and/or a shaded parent
What is the probability of individuals II2 and II8 having white coated offspring? Show all working. Bb x bb = ½ Bb black ½ bb white

22. Pedigree problem 4
Is this trait dominant or recessive? Give reasons to justify your answer.
Is this trait autosomal or sex-linked? Give reasons to justify your answer.
Which individuals are definitely heterozygous?
What is the probability of individuals II1 and II7 have white coated offspring? Show all working.

23. Pedigree problem 4
r = dark
R = white
Is this trait dominant or recessive? Give reasons to justify your answer. dominant
Is this trait autosomal or sex-linked? Give reasons to justify your answer. autosomal
Which individuals are definitely heterozygous? Shaded ones with unshaded children and/or an unshaded parent
What is the probability of individuals II1 and II7 have white coated offspring? Show all working. rr x rr = all rr dark

24. Pedigree problem 5
Is this trait dominant or recessive? Give reasons to justify your answer.
Is this trait autosomal or sex-linked? Give reasons to justify your answer.
Which individuals are definitely homozygous?
Which individuals are definitely heterozygous?
Individuals II8 and II9 are expecting another child. What is the probability it will be normal? Show all working.
Individual II1 is marrying a woman from a family which is free of this disease. What is the probability of their children having this disease? Show all working.

25. Pedigree problem 5 XD Xd Xd XDXd XdXd Y XDY XdY
Is this trait dominant or recessive? Give reasons to justify your answer. Recessive : d = disease, D = normal
Is this trait autosomal or sex-linked? Give reasons to justify your answer. Sex linked
Which individuals are definitely homozygous? Shaded females
Which individuals are definitely heterozygous? Unshaded females with shaded children and/or a shaded parent
Individuals II8 and II9 are expecting another child. What is the probability it will be normal? Show all working. XDXd x XdY = 50% won’t have disease
Individual II1 is marrying a woman from a family which is free of this disease. What is the probability of their children having this disease? Show all working. XDY x XdXd = all XdXd or XdY = 0% with disease

26. Pedigree problem 6
Is this trait dominant or recessive? Give reasons to justify your answer.
Is this trait autosomal or sex-linked? Give reasons to justify your answer.
Which individuals are definitely homozygous?
Which individuals are definitely heterozygous?
Individuals II8 and II9 are expecting another child. What is the probability it will not have the disease? Show all working.

27. Pedigree problem 6 XD Xd XD
XDXD
XDXd Y
XDY
XdY
Is this trait dominant or recessive? Give reasons to justify your answer. Dominant : D = disease, d = normal
Is this trait autosomal or sex-linked? Give reasons to justify your answer. Sex linked
Which individuals are definitely homozygous? Unshaded females
Which individuals are definitely heterozygous? Shaded females with unshaded children and/or an unshaded parent
Individuals II8 and II9 are expecting another child. What is the probability it will not have the disease? Show all working. XDY x XDXd = 25% chance of normal child