Genetics

Question 1

Explain why there is a significant difference b/w observed and expected phenotypic ratios [3]

Answer 1

1. Genes X and Y are linked
2. Allele for Xa and Ya on the same chromosome
3. Allele for Xb and Yb on the same chromosome
4. Greater chance to be inherited together
   » lower chance of crossing over (recombination frequency)

Question 2

How to identify dominant trait

Answer 2

1. Quote cross, full parental phenotypes
2. All offspring have {dominant trait}
   - show how the dominant allele masks the recessive allele

Question 3

Explain the deviation of observed results from the expected dihybrid ratio (test cross) [3]

Answer 3

1. Expected dihybrid ratio is 1:1:1:1, while observed is 4:1:1:4
2. Genes are linked on the same chromosome
   » Xa and Ya on the same chromosome
   » Xb and Yb on the same chromosome
3. Do not undergo independent assortment and segregation

Greater chance to be inherited together
» lower chance of crossing over (recombination frequency) to form recombinant gametes XaYb and XbYa
» Parental combinations of alleles

Question 4

Explain the deviation of observed results from the expected dihybrid ratio (test cross) [3]

Answer 4

1. Expected dihybrid ratio is 1:1:1:1, while observed is 4:1:1:4
2. Genes are linked on the same chromosome
   » Xa and Ya on the same chromosome
   » Xb and Yb on the same chromosome
3. Do not undergo independent assortment and segregation

Greater chance to be inherited together
» lower chance of crossing over (recombination frequency) to form recombinant gametes XaYb and XbYa
» Parental combinations of alleles

Question 5

Explain the purpose of the chi-squared test [1]

Answer 5

Determine if the difference between observed and expected results was significant, or due to chance

Question 6

Describe the inheritance of traits X and Y [2] (you already identified that they linked)

Answer 6

1. Autosomal

2. Xa dominant to Xb, Ya dominant to Yb

Question 7

How to identify recessive trait [1]

Answer 7

1. 2 affected parents give all affected offspring

OR

2. 2 unaffected parents can give a pointed offspring

Question 8

How to identify autosomal trait [2]

Answer 8

1. Males have 2 alleles
2. Sons get 1 allele each from both mother and father, trait not determined just by mother

Thus gene is not on X chromosome

Question 9

Evidence for linked trait [2]

Answer 9

1. Genes X and Y inherited as a unit

2. No recombination observed