Inheritance and Populations Test

b) If individuals 6 and 7 were to have another child, what is the probability this child would be male and blood group A? Explain. (3)

1. 6 must be IA O and 7 must be IB O 2. There is a 0.25 probability blood group will be A 3. Therefore 0.125 probability A and male (0.25/2)

iii. What is the probability the first child of individuals 5 and 5 will be a colour blind boy with a white streak in his hair? (2)

1/8 = 0.125

b) Possible genotypes for a black mouse? (1)

aaDd or aaDD

c) i. 1 in 1000 children has Tay-Sachs. Calculate the percentage of the population you would expect to be heterozygous?

p + q = 100% p² + q² + 2pq = 100% p² = 1/1000 so p = 0.0316... q = 1 - 0.0361... = 0.968... 2pq = 2 x 0.0361... x 0.0968... = 0.06124... x100% = 6.12%

ii. Explain one piece of evidence from he diagram which proves that the allele for Tay-sachs disease is not on the X-chromosome. (2)

1. Female 11 is affected (tt) but male 3 is not (Tt) 2. Therefore 3, father of 11, does not carry the recessive allele t on his x-chromosome (as this would be displayed phenotypically) *females inherit X from both parents, so recessive allele would have to affect the father if sex-linked.

3. Explain why colourblindness, determined by allele Xb, carried on the X chromosome, is more common in men than in women. (2)

1. Males have genotype XY whereas females XX 2. Only one allele of sex-linked genes will be present (as only the X-chromosome can carry) 3. So the recessive allele is always expressed is present 4. Whereas in females, the recessive allele may be masked in heterozygous condition (as dominant can also be present)

b) Tay-sachs disease is a human inherited disorder. Sufferers often die during childhood from Tay-sachs represented as allele t. i. Explain one piece of evidence which proves that the allele for Tay-sachs disease is recessive? (2)

1. Offspring 9 and 11 are affected by Tay-sachs disease 2. However their parents, 3 and 4, are unaffected so must be heterozygous carriers of the recessive Tay-Sachs allele.

d) The sperms in dairy bull same can be separated so that all calves produced are the same sex. i. Explain what causes one of two kinds of sperm to have 3% more DNA? (2)

1. Sperm with 3% more DNA have an X-chromosome 2. Which is larger, containing more genes whereas the other contains Y chromosome which is shorter/less genes

Give a conclusion if chi² is 2.71 and the critical value is 5.99 (2)

1. The calculated chi² value is less than the critical value 2. therefore, there is more than 5% probability that difference is due to chance 3. The null hypothesis should be accepted as there is no significant difference between observed ratios and expected ratios.

ii. Work out the probability Bb XGY male and Bb XGXg female will have a red-green colour blind boy? B: normal cones, b: complete colourblindness, Xg: red-green colourblind.

3/16 = 0.1875

ii. Which antigen or antigens will be present on the plasma membranes red blood cells of individual 5? (1)

Antigen A and B

ii. Give the possible genotypes of the gametes produced by individual 5, XbY hh or individual 6, XBXb Hh (1)

5. Xbh, Yh 6. Xb H, Xb h, XB H, XB, h

ii. Explain why the actual percentage of heterozygotes is likely to be lower in future generations? (1)

Affected individuals are unlikely to reproduce as they often die during childhood (do not pass on the allele)

c) An agouti mouse of unknown genotype was crossed with an albino mouse. Offspring included albino, agouti and black mice. i. Agouti genetype? ii. Two possible albino genotypes?

Albino: __dd Black: aaDd or aaDD Agouti: AA/Aa + Dd/DD i. Aa Dd ii. aa dd or Aa dd

2. a) Explain what is meant by a dominant allele? (1)

An allele which, if present, will be phenotypically expressed.

6. Complete the genetic diagram to show the offspring produced. Actual numbers were Agouti: 34, Black: 35, White:51. Test the hypothesis that there is no significant difference between these results as the expected 1:1:2 ratio.

Calculate expected by doing total number divided according to the ratio. Calculate the sum of (O-E)²/E Degrees of freedom = n-1 = 2 At P = 0.05, the critical value is 5.99.

b) Two alleles Cr (red) and Cw (white) control coat colour. When red cattle were crossed with white cattle, all offspring were roan (had a mixture of red and white hairs). Name the relationship between the two allele that control coat colour? (1)

Codominant

c) Complete colour blindness occurs in the same frequency in males and females, but red-green colour blindness occurs more frequently in males. Explain why? (2)

Complete: equal chance of males and females being homozygous recessive and displaying complete colourblindness Red-green: sex-linked therefore males only need to inherit one recessive allele to be R-G colourblind (whereas females must be homozygous recessive)

iii. Suggest how the actual genotype of the albino parent could be determined? (2)

Cross the albino parent with a black individual aaDd/aaDD (homozygous for yellow banding) If genotype is Aadd, there will be agouti offspring If genotype is aadd no offspring produced with be agouti

5. Coat colour is determined by: A: yellow banding (overall grey appearance) a: no banding therefore black D: required for pigment d: no pigment at all so albino a) What is the gene interaction occurring? Explain. (2)

Epistasis as the gene D (whether or not pigment is produced) influences the expression of gene A

ii. Suggest one reason why farmers would want the calves to be all of the same sex? (1)

In order to have all female cows that produce milk

b) Give the possible genotypes of (diagram) P: red-green colour blind Q: completely colour blind R: Normal vision S: red-green colour blind

P: XgXgBB or XgXgBb Q: bbXgY S: BbXgY

c) Hornless, H is dominant to honed, h. Complete the genetic diagram to show horned, roan cattle crossed with white cattle, heterozygous for hornless.

Phenotype: Horned, roan x hornless, white Genotype: hh CwCr Hh CwCw Gametes (circle!): hCw hCr HCw hCw Offspring G: HhCwCw HhCrCw hhCwCw hhCrCw Offspring P: White less Roan less White horn Roan horn Ratio: 1: 1: 1: 1

1. a) Explain what is meant by the term phenotype? (2)

The observable characteristics of an organism as a result of genotype and interaction with the environment.

4. a) i. How many antigen-determining alleles will be present in a white blood cell? Give a reason. (1)

Two as white blood cells are diploid and an allele is present on each chromosome of the homologous pair.

b) The diagram shows a family tree. i. What are the genotypes of 5 and 6? (2)

XbY hh XBXb Hh

7. a) i. Give all possible genotypes of the gametes from i. man with Bb XGY? ii. women with Bb XGXg

i. B XG, B y, b XG, b y ii. B XG, B Xg, b XG, b Xg