Mendelian Genetics

Question 1

What is Mendel’s first law?

Answer 1

The Law of Segregation: “Two members of a gene pair aggregate into separate gametes; half carrying one member of the pair and the other half the other member”

Question 2

Define the term Pedigree

Answer 2

The recorded ancestry or lineage of a person or family. They show the inheritance of genetic traits

Question 3

What pattern of inheritances does the disease Brachydactyly depict?

Answer 3

It shows a dominant pattern of inheritance

Question 4

What are the symptoms of Brachydactyly?

Answer 4

Shortened fingers and toes due to bone malformation

Question 5

What pattern of inheritance is shown by Huntingtons and how was this discovered?

Answer 5

Dominant inheritance.

• Discovered by Nancy Wexler in a 20 yr study in Maracaibo, Venezuela (incidence is high).
• Allele was found on chromosome 4 leading to development of diagnosis test

Question 6

Name a disease that shows recessive pattern of inheritance

Answer 6

Cystic Fibrosis

Question 7

What is meant by the term Genetic Counselling?

Answer 7

The giving of advice to prospective parents regarding the risks of genetic disorders in the future child

Question 8

What is the equation to calculate the probability of a monohybrid cross?

Answer 8

P (k out of n) = n!/k!(n-k)!×p^k x q^(n-k)

Question 9

What do the terms n, p, k and q refer to in the formula for the probability of a monohybrid cross?

Answer 9

n = number of offspring
p = probability of phenotype under question 
k = number of times outcome p has occured
q = probability of the alternative phenotype (1-p)

Question 10

What is Mendel’s Second Law?

Answer 10

The Law of Independent Assortment: “during the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other.

Question 11

Define the term Dihybrid cross

Answer 11

The inheritance of characters in pairs, i.e. two sets of alleles at a time

Question 12

What was the ratio of SW:SG:WY:WG of the F2 generation in Mendel’s dihybrid cross using the pea plant

Answer 12

SW:SG:WY:WG

9 : 3 : 3 : 1

Question 13

Define the term Recombinant

Answer 13

A recombinant is a new mixture of characteristics in an offspring that didn’t exist in the parents

Question 14

If the number of Heterozygous loci is ‘n’ what is the number of possible types of sperm and egg

Answer 14

2^n

Question 15

If the number of Heterozygous loci is ‘n’ what is the number of possible types of F2 genotypes?

Answer 15

3^n

Question 16

Give an Agricultural example of the benefits of recombination.

Answer 16

The dwarf rice of China and India crossed with short stem low yield and tall stem high yield plant –> short stem high yield plant.

Question 17

Define the term Heterosis

Answer 17

The tendency of a cross-bred individual to show qualities superior to both parents.

Question 18

What is another term for Heterosis?

Answer 18

Hybrid vigour.

Question 19

What causes the symptoms of cystic fibrosis?

Answer 19

The failure of a transport protein that moves liquid across cell membranes which causes the lungs to get clogged up with mucus.

Question 20

Name the 8 genetic aspects that limit Mendelian genetics

Answer 20

Incomplete Dominance, Codominance, Multiple Alleles

Lethal Alleles, Pleiotropy, Gene Interaction, Epistasis and Complementation

Question 21

Define Incomplete Dominance and give an example.

Answer 21

A heterozygote intermediate between the dominant homozygotes. TAY SACHS carriers- have intermediate levels of the HEXOSAMINIDASE A enzyme.

Question 22

Define Co-dominance and give and example

Answer 22

Both phenotypes are seen rather than an average of the two, An example is the ABO blood group system. An AB genotype will make both A and B antigens.

Question 23

Give another example of Co-dominance

Answer 23

Carriers of Sickle cell Anaemia carry both the mutated and normal forms of Haemoglobin

Question 24

Define Multiple Alleles and give an example

Answer 24

An allele of a genetic locus having m ore than two allelic forms within a population. An example is the ABO blood type locus.

Question 25

Define the term Lethal Alleles and give an example.

Answer 25

Alleles that cause an organism to die only in the homozygous form. Achondroplasia (dwarfism) is lethal in the homozygous.

Question 26

What is the cause of the symptoms of Achondroplasia?

Answer 26

A mutation in the fibroblast growth factor receptor 3 gene (FGFR3)

Question 27

Define the term Pleiotropy.

Answer 27

The principle that one gene with visible effects influences many characteristics simultaneously

Question 28

Explain why all blue eyed cats are deaf.

Answer 28

Pleiotropic effect. These cats lack melanin causing blue eyes and melanin also used in inner ear process of sound.

Question 29

Give an example of Pleiotropy.

Answer 29

Sickle cell haemoglobin caused by point mutation (glu subbed for val); has effects on kidney, heart and brain.

Question 30

Define Gene Interaction

Answer 30

Several Genes affecting one characteristic.

Question 31

Give an example of Gene Interaction

Answer 31

Sex Limitation - the expression of a particular characteristic limited to one gender. Sex limited genes often respond to sex hormones of a particular sex.

Question 32

Give an example of Sex limitation

Answer 32

Pattern Baldness- hets male go bald due to production of testosterone but hets female no baldness due to lack of testosterone.

Question 33

Define Epistasis. How is this an example of Gene Interaction?

Answer 33

The suppression of the effect of one gene by another.

Question 34

Give an example of Epistasis.

Answer 34

Male pattern baldness- this gene is epistatic toward the gene for hair colour.

Question 35

Give an example of Epistasis

Answer 35

Albinism- the gene for albinism is epistatic towards the genes for skin pigmentation.

Question 36

What is the Secretor Phenotype an example of?

Answer 36

Gene interaction. Secretor Phenotype involves the interaction between ABO locus and Se locus. Homo or het Se will produce ABO substances in saliva/sperm.

Question 37

Define Complementation.

Answer 37

When two strains of an organism with different homo recessive mutations produce the same mutant phenotype or wildtype when mated.

Question 38

Give an example of Complementation in plants

Answer 38

The white and purple foxglove- WT is purple. When white plants from diff populations crossed, the WT purple is F1.

Question 39

Give an example of Complementation of in humans.

Answer 39

Deafness- many different loci affect hearing due to different components involved in sound. Offspring of two deaf people often leads to WT normal hearing.

Question 40

Give an example of Incomplete Dominance in plants.

Answer 40

Mirabilis Japonica- 4 o’ clock plant can be RR (red) or WW (white). Red crossed with white plants produces RW which are pink.