Monogenic Inheritance 20.2

Question 1

Explain how to do a genetic cross.

Answer 1

1. State the phenotypes of the parents
2. State the genotypes of the parents (Assign a letter to represent alleles, capital for dominant, lower case for recessive)
3. State the gametes (circles them)
4. Use a Punnett square to show the results of random fertilisation of gametes
5. State the proportion of each genotype which are produced among the offspring
6. State the phenotypes

Question 2

What is codominance

Answer 2

When 2 different alleles occur for a gene - both of which are equally dominant. Both genes are expressed in the phenotype

Question 3

How are genes and alleles represented during a codominance genetic cross

Answer 3

A letter is chosen to represent the gene then another letter is used to represent the allele (j subscript)

Question 4

What are the 3 alleles for immunoglobulin

Answer 4

I^A = Antigen A
I^B = Antigen B
I^O = neither antigen

Question 5

Which alleles for immunoglobulin are codominant and which is recessive?

Answer 5

Codominant = I^A & I^B
Recessive = I^O

Question 6

Which combination of alleles for immunoglobulin would result in blood Group A

Answer 6

I^A I^A

I^A I^O

Question 7

Which combination of alleles for immunoglobulin would result in blood Group B

Answer 7

I^B I^B

I^B I^O

Question 8

Which combination of alleles for immunoglobulin would result in blood Group AB

Answer 8

I^A I^B

Question 9

Which combination of alleles for immunoglobulin would result in blood Group O

Answer 9

I^O I^O

Question 10

Difference between X & Y chromosome

Answer 10

X chromosome is larger and contains genes not involved in sexual development.

Y chromosome is small and contains almost no genetic info, but carries a gene that causes the embryo to develop as a male

Question 11

Why are some characteristics/ diseases more likely to occur in males?

Answer 11

Y chromosome much smaller, so some characteristics that are carried on only on the X chromosome - the male will only inherit one copy.

So any recessive allele on the inherited X chromosome will be expressed.

Question 12

How are alleles represented during sex linkage

Answer 12

The alleles are linked to the chromosome they are found on

Question 13

What is special about the phenotypes formed as a result of a gene which has codominant alleles (2)

Answer 13

Codominant alleles are as equally dominant

A heterozygous individual would display a phenotype caused by the expression of both alleles

Question 14

Using a genetic cross show the blood groups of the potential offspring of a father with the blood group AB and a mother with blood group O

Answer 14

Mother: Homozygous I^O I^O
Father: Heterozygous I^A I^B

50% of offspring would be I^A I^O (Group A)
50% I^B I^O (Group B)

Question 15

Define monogenic inheritance

Answer 15

Where one phenotypic characteristic is controlled by a single gene