Inherited Changes

Question 1

Explain the meanings of the terms haploid and diploid.

Answer 1

Haploid - Cell that consists of a single set of chromosomes.

Diploid - Cell that consists of two complete sets of chromosomes.

Question 2

Explain what is meant by homologous pairs of chromosomes.

Answer 2

A pair of chromosomes that contain the same genes in the same positions and the same position of their centromere.

Question 3

Explain the need for a reduction division during meiosis in the production of gametes.

Answer 3

Gamete cells contain half the number of chromosomes (23) so that when they fuse, the chromosome number is restored (46). This is done to prevent chromosome number from doubling during fertilisation.

Question 4

Which genetic process gives rise to production of gametes?

Answer 4

Meiosis

Question 5

Describe the events of meiosis I.

Answer 5

Prophase I - Centrosomes move to opposite poles of the cell, homologous chromosomes pair up. Crossing over occus here.

Metaphase I - Homologous pair of chromosomes (bivalent) line up at the metaphase plate.

Anaphase I - Bivalent is separating.

Telophase I - Cell divides and two daughter cells are formed.

Question 6

Describe the events that take place in Meiosis II.

Answer 6

Prophase II - Centrosomes move to opposite poles of the cell.

Metaphase II - Single chromosomes line up along metaphase plate.

Anaphase II - Spindles pull sister chromatids apart to opposite poles of the cell.

Telophase II - Nuclear envelopes reform. Four genetically different daughter cells are produced, each with the haploid number of chromosomes.

Question 7

Explain the term crossing over and how it results in genetic variation.

Answer 7

During prophase I, there is exchange of genes between non-sister chromatids at the chiasmata which produces different combinations of alleles on the two chromosomes and leads to formation of recombinants.

Question 8

Explain the term independent assortment and how it results in genetic variation.

Answer 8

During metaphase I, the homologous pair of chromosomes align randomly along the equator. Thus in the daughter cells of meiosis I, there will be a mix of maternal and paternal chromosomes, increasing genetic variation.

Question 9

Why is random fusion of gametes important?

Answer 9

It increases genetic variation due to the random combination of chromosomes generated.

Question 10

What is a gene?

Answer 10

A section of DNA that codes for a particular protein.

Question 11

What is meant by the term locus?

Answer 11

Position of genes on a chromosome.

Question 12

What is an allele?

Answer 12

Alternative form of a gene.

Question 13

What is meant by dominant and recessive allele?

Answer 13

Dominant allele - An allele that is always expressed in the phenotype when present, even in the presence of an alternative allele.

Recessive allele - An allele that is only expressed in its homozygous form.

Question 14

Describe the term ‘linkage’.

Answer 14

Two or more genes are said to be linked if they are found on the same chromosomes and are inherited together because there is no independent assortment.

Question 15

What is a test cross?

Answer 15

Crossing an individual showing the dominant trait and having an unknown genotype with an individual showing the recessive trait.

Question 16

What is meant by F1 and F2 generation?

Answer 16

F1 generation - Offspring produced from first filial parents.

F2 generation - Offspring produced from first filial parents.

Question 17

Define the terms phenotype and genotype.

Answer 17

Phenotype - Observable features of an organism as a result of alleles present.

Genotype - Genetic make-up of an organism in terms of alleles present.

Question 18

Define the terms homozygous and heterozygous.

Answer 18

Homozygous - Having two identical alleles of a particular gene.

Heterozygous - Having two different alleles of a particular gene.

Question 19

What is a monohybrid cross?

Answer 19

Cross that involves one pair of contrasting traits.

Question 20

Define the term sex linkage.

Answer 20

Two or more genes found a sex chromosome (X chromosome) that are inherited together because there is no independent assortment.

Question 21

Define the term autosomal linkage.

Answer 21

Genes that are inherited together because they are located very close to each other on the same non-sex chromosome.

Question 22

What is meant by the term ‘codominance’?

Answer 22

Both alleles express equal dominance producing a third phenotype or blend of the parental phenotype in the heterozygous which is different from the homozygous.

Question 23

Define the term multiple allelism.

Answer 23

Two or more alleles coding for the same gene.

Question 24

What is dihybrid inheritance?

Answer 24

Kind of genetic inheritance in which parents differ in two traits.

Question 24

What is dihybrid inheritance?

Answer 24

Kind of genetic inheritance in which parents differ in two traits.

Question 25

Explain why a man with haemophilia cannot pass it on to his son but can pass it on to his grandson.

Answer 25

Sex linked gene found on X chromosome. There is no sex linked gene on Y chromosome. Son inherits Y chromosome from the father meaning he cannot get haemophilia. Father passes on X chromosome to daughter meaning she becomes a carrier. She then passes the X chromosome containing the haemophilia gene to her son when she gives birth, thus the grandson acquires it.