Grade 12 - Life at Molecular, Cellular and Tissue level - Genetics and genetic engineering

Question 1

What is genetics?

Answer 1

• A branch of biology that studies heredity and variation in organisms.
• It tries to explain both the similarities and the differences between the parents and their offspring.
• Parents always produce offspring that look like them in some ways but differ tin other ways Why?
• Heredity = passing on of traits / characteristics from one generation to the next.

Question 2

Who was the father of genetics?

Answer 2

Gregor Mendel (1822 - 1884) Austrian monk lived about same time as Darwin

Question 3

What was Mendel’s breakthrough that earned him the title “Father of Genetics”?

Answer 3

• Study of heredity by investigating the transfer of characteristics from one generation to the next.
• He realised that something is passed on from parent to offspring and that sexual reproduction combines these somethings from each parent to produce offspring which are unique, yet the same.
• 1886 - published his work, but only recognised in scientific circles from 1900 (after his death).
• His research formed the basis of many other scientists’ research.
• Pea plant experiment.

Question 4

What are Mendel’s ‘factors’?

Answer 4

Today we refer to it is ‘genes’ - which are part of DNA molecules and chromosomes.
The “somethings” which are passed from parent to offspring are genes.

Question 5

Does the amount of genetic material reflect the level of advancement of an organism?

Answer 5

No.
Example - Some** ferns** have over 600 chromosomes
Lung fish, a primitive fish, has forty times more DNA than humans.
Why? Large number of repetitive DNA molecules.

Question 6

Define a gene:

Answer 6

A section of DNA (series of nucleotides / bases) that controls hereditary characteristics (traits)
= i.e. is the basic unit of heredity in living organisms.

Question 7

What is each chromatid made up of?

Answer 7

One, helical DNA molecule.

Question 8

What is each DNA molecule made up of?

Answer 8

A series of genes.

Question 9

Each chromosome has between several hundred and several thousand genes. What is the total number of genes in humans thought to be?

Answer 9

Between 20 000 and 25 000.

Question 10

Nearly all somatic cells have an exact copy of all the genes in that organism.

OR

Define ALLELES

Answer 10

• Because there are two of each kind of chromosome (paternal and maternal), each cell contains two of each kind of gene (before replication).
• These versions of a gene are known as alleles.

Question 11

What is the gene pool?

What does a large gene pool v a small gene pool indicate?

Answer 11

• The set of genes, or genetic information, in a population of sexually reproducing organisms.
• A large gene pool indicates high genetic diversity and increased chance of survival.
• A small gene pool indicates **low genetic diversity **and increased possibility of extinction.

Question 12

How active are genes?

Answer 12

• Although each cell contains a full compliment of DNA, only the genes that are needed are activated and the others are suppressed.
• Different genes are activated in different cells, creating the specific proteins that give a specific cell character e.g. bone cells, brain cells, skin cells, etc.
• Some genes active in early development and inactive later. =
• Genes active in making proteins needed for basic function = housekeeping genes.
• Non-coding genes - they don’t code for proteins and occur in-between the coding sections. (only about 2% code for protein)

Question 13

What are non-coding genes?

Answer 13

They don’t code for proteins and occur in-between the coding sections. (only about 2% code for protein)

Question 14

What are non-coding genes?

Answer 14

They don’t code for proteins and occur in-between the coding sections. (only about 2% code for protein)

Question 15

What are hox genes?

Answer 15

Master control genes that determine the way in which the body develops from a single zygote

Question 16

Define epigenetics:

Answer 16

• The control of genes
• (Human Epigenome Project) - aims to record what switches genes on and off.

Question 17

Define Alleles:

Answer 17

• One of two or more forms of a gene (from the word alllemorph - alternative form).
• Genes responsible for controlling different versions of a trait / characteristic found in the same locus on homologous chromosomes.
• E.g. for the gene determining colour in cattle, one allele could determine a black coat (B) and another allele a white coat (b).

Question 18

How are alleles represented?

Answer 18

• Letters
• Capital letter - denotes dominant allele
• Lower case letter - recessive allele

Question 19

How are alleles passed from parent to offspring?

Answer 19

• By way of chromosomes in the gametes that are made by the process of meiosis in the sex organs.
• gamete = a reproductive cell / sex cell

Question 20

Summarise in short meiosis to show how the alleles are segregated.

Answer 20

Revision textbook page 163 - 164

Question 21

Define genotype:

Answer 21

• Made up of all the genes an organism carries on its chromosomes which it has inherited from its parents.

Question 22

Define phenotype:

Answer 22

• The physical appearance of an organism, such as tallness, hair colour.
• It is partly programmed by genes, its genotype, but also shaped by external factors such as exercise, diet and environment.

Question 23

Explain Homozygous

Answer 23

• The pair of alleles at a locus are the same, organism is homozygous for that particular trait
• e.g. both alleles will determine a black coat in cattle** (BB)**

Question 24

Explain Heterozygous

Answer 24

If the pair of alleles at a locus are different, the organism is heterozygous (a hybrid) for that particular trait
E.g. one allele determining a black coat and the other a white coat in cattle (Bb)

Question 25

What is a dominant allele?

Answer 25

In a heterozygous pairing, one allele of a pair may be dominant, in that the trait is expressed in the offspring, e.g. black coat.

Question 26

What is a recessive allele?

Answer 26

• In a heterozygous pairing, one allele of a pair may be recessive, in that the trait is suppressed in the presence of the dominant allele and not expressed in the offspring.

See example textbook diagram - page 164

Question 27

What is a monohybrid cross?

Answer 27

A cross between parents with different alleles for a single gene.

Question 28

What is the function of a genetic diagram?

Answer 28

Show how characteristics are inherited.

Question 29

Explain what a pungent square is:

Answer 29

An easy way to represent a cross between two organism for any number of characteristics for which the parental genotype are known.

It predicts probability of the offspring’s genotype and phenotype and is the basic tool used for Mendelian genetics.

Question 30

Discuss Mendel’s experiment in great detail.

Answer 30

Textbook pages 166 - 167

Question 31

What do you understand by complete dominance, as shown in Mendel’s experiment.

Answer 31

#

Question 32

State Mendel’s law of segregation:

Answer 32

During meiosis, allele pairs separate (segregate) so that the gametes have a single allele for each characteristic.

Question 33

State Mendel’s law of dominance:

Answer 33

In a cross of parents that are pure for contrasting traits, only the dominant trait will appear in the phenotype. Recessive alleles will always be masked by dominant alleles.

Question 34

State Mendel’s law of independent assortment:

Answer 34

The alleles of different genes (e.g. height of plant and colour of flower) segregate randomly and independently of one another during the gamete formation.

Question 35

Mature red blood cells have no nuclei, therefore no chromosomes and no genes. Why?

Answer 35

Answer

Question 36

Why are normal body cells / somatic cells diploid? (2n)

Answer 36

• They have a pair of homologous chromosomes.
• Two alleles which may be same or different.

Question 37

Why are sex cells haploid (n)?

Answer 37

• One of a pair of homologous chromosomes.
• One of each pair of alleles.