Exam Qs:Genetic Crossing DNA And RNA

Question 1

In a breed of cattle there is incomplete dominance between the allele for red coat and the allele for white coat. Heterozygous individuals are roan.
In each of the following find the percentage chance that a calf of the cross will have a roan coat
i)roan x white
ii)roan x red
iii)roan x roan

Answer 1

i) 0%
ii) 50%
ii) 25%

Question 2

In genetics what is meant by the term sex linkage?

Answer 2

A characteristic that is controlled by a gene on the sex chromosome

Question 3

Would human females or human males be more likely to suffer from sex-linked diseases such as hemophilia?

Answer 3

Males would be more likely to suffer from sex-linked diseases.

Question 4

i)Would human females or human males be more likely to suffer from sex-linked diseases such as hemophilia?
Explain your answer to part i) by referring below to possible genotypes and their corresponding phenotypes.
Male:
Female:

Answer 4

Male: If the male receives one allele for haemophilia he will have the condition, as there is no gene on the Y chromosome. There are only two possible genotypes XHY or XhY with two possible phenotypes haemophiliac or not. There is no heterozygous condition.

Female:Because the female has two genes it is possible to be a carrier. A female genotype XHXh will not have haemophilia

Question 5

Diseases in humans occur for a number of different reasons . Explain how the presence of a named genetically sex-linked disease other than haemophilia may be recognized.

Answer 5

Colour blindness:Inability to distinguish certain colours

Question 6

Most organisms contain both nucleic acids, RNA and DNA.
(i) Name the biologically active entities, each of which contains only one type
of nucleic acid.
(ii) Name two locations in eukaryotic cells where RNA but no DNA is found.

Answer 6

i)RNA
Viruses
ii)Ribosomes and Cytoplasm

Question 7

As a result of Gregor Mendel work, he put forward two laws, the Law of Segregation and the Law of Independent Assortment. State each of these laws.

Answer 7

The Law of Segregation states that inherited characteristics are controlled by pairs of factors (now called genes) and that these pairs of factors segregate from each other at gamete formation.

The Law of Independent Assortment states that when gametes are formed, either of a pair of factors is equally likely to combine with either of another pair of factors.

Question 8

Explain how then results of a cross between green dwarf pea plant (homozygous recessive) and a heterozygous plant would differ if the genes for height and seed colour were linked

Answer 8

If the genes for height and seed colour were linked then independent assortment could not occur; therefore, there would be no gametes Ty and tY and no offspring Ttyy or ttYy, so there would be no tall green plants or dwarf yellow ones.