GENETICS AND INHERITANCE

Question 1

WHO IS THE ‘FATHER’ OF GENETICS

Answer 1

Gregor Mendel

Question 2

DEFINE THE CONCEPTS OF GENES AND ALLELES IN INHERTITANCE

Answer 2

GENES:
* a segment of DNA in a chromosome that contains the code for a particular characteristic

ALLELES:
* different forms of a gene which occur at the same locus on homologous chromosomes

Question 3

DEFINE THE CONCEPTS OF DOMINANT AND RECESSIVE ALLELES

Answer 3

• one allele of a gene pair can mask another and this is known as the dominant allele. the allele that is masked and not visibly expressed in the organism, is called recessive

Question 4

DEFINE THE CONCEPTS OF A GENOTYPE AND PHENOTYPE IN INHERITANCE

Answer 4

1. the genetic composition of an organism is known as the genotype
2. the physical appearance of an organism determined by the genotype, is known as its phenotype

Question 5

DEFINE THE CONCEPTS OF HOMOZYGOUS AND HETEROZYGOUS IN INHERTITANCE

Answer 5

• when two alleles for a particular characteristic on the homologous chromosomes are the same
• when two alleles on the homologous chromosomes differ from each other, the individual is heterozygous for that particular trait

Question 6

DEFINE THE LAW OF DOMINANCE

Answer 6

• when 2 homozygous organisms with contrasting characteristics are crossed, all the individuals of the F1 generation will display the dominant trait.
• an individual that is heterozygous for a particular characteristic will have the dominant trait as the phenotype

Question 7

EXPLAIN MENDEL’S PRINCIPLE OF SEGREGATION

Answer 7

• an organism posseses two ‘factors’ which seperate or segregate so that each gamete contains only one of these ‘factors’

Question 8

DESCRIBE THE DIFFERENT TYPES OF DOMINANCE

Answer 8

COMPLETE DOMINANCE:
* one allele is dominant and the other is recessive, such that the effect of the recessive allele is masked by the dominant alelle in the heterozygous condition

INCOMPLETE DOMINANCE:
* neither one of the two alleles of a gene is dominant over the other, resulting in an intermediate phenotype in the heterozygous condition

CO-DOMINANCE:
* both alleles of a gene are equally dominant whereby both alleles express themselves in the phenotype in the heterozygous condition

Question 9

EXPLAIN BLOOD GROUPING

mention the different alleles and their different combinations, as well as the type of dominance each allele contains

Answer 9

• there are four blood types in humans: A, B, AB or O

blood groups and their genotypes:
* A - I^A I^A or I^A i
* B - I^B I^B or I^B i
* AB - I^A I^B
* O - ii

Question 10

EXPLAIN MENDEL’S PRICIPLE OF INDEPENDANT ASSORTMENT

Answer 10

• the various ‘factors’ controlling the different characteristics are seperate entities, not influencing each other in any way, and sorting themselves out independantly during gamete formation

Question 11

DEFINE SEX-LINKED ALLELES AND SEX-LINKED DISORDERS

Answer 11

• the gonosomes not only control gender, but also carry sex-linked genes
• sex-linked disorders occur more often in males than in females as males only have one X chromosome
• if an abnormal allele occurs on the X-chromosome of the male, that characteristic will form part of his phenotype and he will suffer from the genetic disorder. he has no other X chromosome that may carry a normal allele to mask the abnormal allele.
• however, when a female, who has two X chromosomes, carries an abnormal recessive allele on one X. chromosome, there is a good chance that she will carry a normal dominant allele on her other X chromosome.
• this normal dominant allele masks the abnormal recessive allele and she will not suffer from the genetic disorder. she is known as a carrier.
• in females, a characteristic caused by a recessive allele will only be expressed in the phenotype if both X chromosomes carry the recessive gene

Question 12

DESRIBE THE DIFFRENT GENOTYPES OF A HAEMOPHILIAC

Answer 12

• X^H X^H - normal female
• X^H X^h - normal female
• X^h X^h - haemophiliac female
• X^H Y - normal male
• X^h Y - haemophiliac male

Question 13

EXPLAIN WHAT A GENETIC LINEAGE/PEDIGREE IS USED FOR

Answer 13

• a pedigree traces the inheritance of characteristics over many generations

Question 14

HOW TO IDENTIFY DOMINANCE IN A GENETIC CROSS

Answer 14

COMPLETE DOMINANCE:
1. a letter is usually chosen according to the dominant allele
2. the uppercase form of the letter will represent the dominant allele
3. the lowercase form of the letter will represent the recessive allele

INCOMPLETE DOMINANCE:
1. no allele is dominant over the other.
2. two letters are chosen, one for each allele
3. third phenotype, as a result, is a combination of the two alleles

CO-DOMINANCE:
1. two letters are chosen, one for each allele
2. offsprings will have a phenotype that will have equal distributions of the alleles

Question 15

DEFINE MUTATION AND GENE MUTATION

Answer 15

mutation:
* any change in the genotype of an organism

gene mutation:
* occurs as a result of a change in the nucleotide sequence in the DNA molecule

Question 16

DESCRIBE THE EFFECTS THAT OCCUR DURING HARMFUL MUTATIONS

Answer 16

• can cause genetic disorders.
• most disorders caused by genes on autosomes are caused by recessive genes, and are called autosomal recessive disorders.
• disorder caused by dominant genes are called autosomal dominant disorders.
• albinism and sickle-cell disorder are examples of autosomal recessive disorders

Question 17

DESCRIBE THE EFFECTS OF USEFUL MUTATIONS

Answer 17

• can be advantageous to the organism and they are passed on from parent to offspring.
• these mutations also change the DNA responsible for the production of a specific protein.
• if the protein made increases the organism’s chance for survival, it would be seen as a useful mutation

Question 18

DESCRIBE THE EFFECTS OF HARMLESS MUTATIONS

Answer 18

• occur in the non-coding DNA and have no effect on the structure or functioning of the organism

Question 19

DEFINE BIOTECHNOLOGY

Answer 19

the manipulation of biological processes to satisfy human needs

Question 20

EXPLAIN THE USES AND SOURCES OF STEM CELL RESEARCH

Answer 20

harvested stem cells are placed in the damaged area and stimulated to develop into the same cell type.

USES:
1. bone marrow has been used for a long time to treat cancers
2. stem cells are used to replace dead cells in the heart after a heart attack or growing skin tissue to treat burn victims or growing nerve cells to treat spinal cord injuries and parkinson’s disease

SOURCES:
1. stem cells may be harvested from the placenta, embryos, bone marrow and from blood in the umbilical cord.

Question 21

DESCRIBE A BRIEF OUTLINE OF THE PROCESS OF GENETICALLY MODIFIED ORGANISMS

EXPLAIN THE PRODUCTION OF INSULIN

Answer 21

synthetic insulin is used to treat diabetes and is produced by genetic engineering technology:
1. the DNA with the gene coding for the production of insulin is removed from healthy human pancreatic cells
2. enzymes are used to cut the DNA into segments to isolate the specific gene
3. a plasmid is removed from a bacterial cell
4. the plasmid is cut using enzymes
5. the human insulin gene is inserted into the plasmid to form recombinant DNA
6. the recombinant DNA is placed back into the bacterial cell
7. the bacteria are placed in a fermentation tank where they reproduce rapidly to produce many copies of the insulin gene
8. the insulin is extracted from the bacteria and purified

Question 22

DEFINE THE BENEFITS OF GENETIC MODIFICATION

Answer 22

• produce crops that are resistant to adverse conditions
• increase crop yield
• change the time for the ripening of fruit
• increase shelf life of plant products
• improve nutritional value of food
• improve taste of food
• developing plants with desirable characteristics
• production of drugs or hormones which have fewer side-effects and is cheaper

Question 23

DESRIBE THE PROCESS OF DNA CLONING

EXPLAIN THE PROCESS IN ANIMALS AND PLANTS

Answer 23

ANIMALS:
* the nucleus of an ovum is removed and replaced with the nucleus of a somatic donor cell/ diploid donor cell
* the zygote is stimulated for mitosis to occur
* the embryo is then placed into the uterus of an adult female

PLANTS:
* plants may be cloned by vegetative reproduction/asexual reproduction/tissue culture/grafting
* a plant with the desired characteristics is selected
* a vegetative part of the ‘parent’ plant structure is removed and placed inside a growth medium and allowed to grow

Question 24

EXPLAIN THE BENEFITS OF CLONING

Answer 24

• to produce organisms with desired traits
• conservation of threatened species
• to create tissues/organs for transplant

Question 25

DESCRIBE THE USE OF BLOOD GROUPING AND DNA PROFILES IN PATERNITY TESTING

Answer 25

BLOOD GROUPING:
* the blood group of a child is determined by the alleles received from both parents
* the blood group of the mother, the child and the possible father is determined
* if the blood group of the mother and possible father cannot lead to the blood group of the child, the man is not the father
* if the blood group matches, the man might be the father. this is not conclusive as many man have the same blood type

DNA PROFILES:
* a child received DNA from both parents
* the DNA profiles of the mother, child and possible father are determined
* a comparison of the DNA bands of mother and child are determined
* the remaining DNA bands are compared to the possible father’s DNA bands
* if all the remaining DNA bands in the child’s profile match the possible father’s DNA bands then the possible father is the biological father
* if all the remaining DNA bands in the child’s profile does not match the possible father’s DNA bands then the possible father is not the biological father

Question 26

EXPLAIN THE MUTATIONS ON MITOCHONRIAL DNA USED IN TRACING FEMALE ANCESTRY

Answer 26

• mitochondrial DNA is found in mitochondria
• mtDNA mutates at a regular rate so scientists are able to analyse these mutations to work out a timeline of genetic ancestry
• only the mother’s mtDNA is passed on to her offspring
• analysis of mutations show that the oldest female ancestors of humans are from africa