Chapter 9 - Inheritance.

Question 1

What is a gene?

Answer 1

A sequence of DNA that codes for a polypeptide and which occupies a specific locus on a chromosome.

Question 2

What is an allele?

Answer 2

A variant nucleotide sequence for a particular gene at a given locus, which codes for an altered phenotype.

Question 3

What is the locus of a gene?

Answer 3

Its position on a chromosome.

Question 4

What does it mean if an individual is heterozygous for a gene?

Answer 4

If the alleles from that particular gene are different from both parents.

Question 5

What does it mean if an individual is homozygous for a gene?

Answer 5

If the alleles of a particular gene are the same from each parent.

Question 6

What is the genotype of an individual?

Answer 6

It is all the alleles they contain.

Question 7

What is the phenotype of an individual?

Answer 7

Can be described as their appearance. It is the way the genotype is expressed in a specific environment.

Question 8

When is a recessive characteristic presented?

Answer 8

Only when it is homozygous.

Question 9

What does it mean if a characteristic is dominant?

Answer 9

If its always expressed when present.

Question 10

What is it called if both alleles contribute to the phenotype?

Answer 10

Co-dominance.

Question 11

What is monohybrid inheritance?

Answer 11

It is the inheritance of a single gene.

Question 12

What does a diagram of a genetic cross have to show?

Answer 12

• The generations, I.e. parents, F1 etc.
• The genotypes of parents and offspring.
• The phenotypes of parents and offspring.
• The alleles present in gametes.

Question 13

What is a test cross/back cross?

Answer 13

A cross between an individual with the phenotype of the dominant characteristic, but unknown genotype, with an individual that is homozygous recessive for the gene in question.

Question 14

What is Mendel’s 1st law?

Answer 14

The law of segregation; The characteristics of an organism are determined by factors (alleles) which occur in pairs.

Question 15

What is dihybrid inheritance?

Answer 15

It is the simultaneous inheritance of 2 unlinked genes.

Question 16

What ratio does a Dihybrid cross show if 2 of the F1 generation are crossed?

Answer 16

9:3:3:1.

Question 17

What does it mean if genes are ‘linked’?

Answer 17

It means that the genes are on the same chromosome and therefore don’t segregate independently during meiosis.

Question 18

What is the difference between complete and incomplete linkage?

Answer 18

Complete - No crossing over has occurred.

Incomplete - Crossing over has occurred.

Question 19

What is the usual ratio of a complete linkage?

Answer 19

3:1.

Question 20

What is the null hypothesis in a chi squared test?

Answer 20

It states that there is no difference between the observed and expected results of a cross.

Question 21

How do you work out the degrees of freedom for a chi-squared test?

Answer 21

It is one less than the number of classes of data.

Question 22

What is the name of the sex chromosomes?

Answer 22

Heterosomes.

Question 23

What does it mean if a gene is sex linked?

Answer 23

The gene is carried by a sex chromosome so that a characteristic it encodes is seen predominately in one sex.

Question 24

What is a mutation?

Answer 24

It is a change in the amount, arrangement or structure in the hereditary material of an organism, either DNA or RNA in viruses.

Question 25

What can increase the rate of a gene mutation?

Answer 25

• Ionising radiation.

- Mutagenic chemicals.

Question 26

What are the different ways in which mutation can happen?

Answer 26

• Gene/point mutation, DNA not copied accurately in interphase.
• Chromosome mutation, chromosomes may get damaged and break. They then may repair themselves incorrectly.
• Aneuploidy, whole chromosomes lost or added.
• Polyploidy, number of chromosomes may double if cells fail to divide after fertilisation.

Question 27

What are the different types of point/gene mutation?

Answer 27

• Addition, a base is added.
• Duplication, same base incorporated twice.
• Subtraction, a base is deleted.
• Substitution, a different base in incorporated.
• Inversion, adjacent bases on the same DNA strand exchange position.

Question 28

What is it called if the new codon codes for the same amino acid so there is no change to the polypeptide?

Answer 28

A silent mutation.

Question 29

What is down syndrome caused by?

Answer 29

Non-disjunction.

Question 30

What is non-disjunction?

Answer 30

A faulty cell division in meiosis following which one of the daughter cells receives 2 copies of a chromosome and the other receives none.

Question 31

What is a carcinogen?

Answer 31

An agent that causes cancer.

Question 32

What are tumour suppressor genes?

Answer 32

Genes that regulate mitosis and prevent cells dividing too quickly.

Question 33

What is the difference between a benign tumour and a malignant tumour?

Answer 33

• Benign, usually harmless as it doesn’t invade surrounding tissues or spread to other parts of the body.
• Malignant, harmful as they spread around the body and invade other tissues, making secondary tumours.

Question 34

What is an oncogene?

Answer 34

A proto-oncogene with a mutation that results in cancer.

Question 35

How may an oncogene occur?

Answer 35

• If a mutation causes chromosomes to rearrange and places the proto-oncogene next to a DNA sequence that permanently activates it.
• There is an extra copy of the proto-oncogene resulting in too much of its product being made, causing excessive mitosis.

Question 36

What is epigenetics?

Answer 36

The control of gene expression by modifying DNA or histones, but not by affecting the DNA nucleotide sequence.

Question 37

What is Mendels 2nd law?

Answer 37

Mendel’s second law is also known as the law of independent assortment. The law of independent assortment states that the alleles of one gene sort into gametes independently of the alleles of another gene.