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Question 1

Inheritance

Answer 1

Inheritance is the transmission of genetic information from one generation to the next, leading to continuity of the species and variation within it.

Question 2

Chromosome

Answer 2

A thread of DNA, made up of genes.

Question 3

Allele

Answer 3

An alternative form of a gene. Pairs of alleles occupy the same relative positions on chromosome pairs.

Question 4

Gene

Answer 4

A section of DNA, which codes for the formation of a protein controlling a specific characteristic of the organism.

Question 5

Haploid nucleus

Answer 5

A nucleus containing a single set of unpaired chromosomes, e.g. in sperm and ova (eggs). In humans, the haploid number is 23.

Question 6

Diploid nucleus

Answer 6

A nucleus containing pairs of chromosomes, e.g. in somatic (body) cells, In humans the diploid number is 46.

Question 7

Genotype

Answer 7

The genetic make-up of an organism, e.g. Tt, where T and t are alleles of a gene.

Question 8

Phenotype

Answer 8

The characteristics visible in an organism, controlled by the genotype, e.g. a tall plant or a dwarf plant.

Question 9

Homozygous

Answer 9

Having a pair of identical alleles controlling the same characteristics, e.g. TT, where T=tall. The organism will be pure-breeding for that characteristics.

Question 10

Heterozygous

Answer 10

Having a pair of dissimilar alleles for a characteristic, e.g. Tt.

Question 11

Dominant

Answer 11

A gene, e.g. T, that always shows in the phenotype of an organism whether the organism is heterozygous (Tt) or homozygous (TT).

Question 12

Recessive

Answer 12

A gene, e.g. t, that only has an effect on the phenotype when the organism is homozygous (tt)

Question 13

chromosome

Answer 13

In the nucleus of every cell there are a number of long threads called chromosomes.

Question 14

Most of the time, the chromosomes are too thin to be

Answer 14

seen except with an electron microscope. But when a cell is dividing, they get shorter and fatter so they can be seen with a light microscope.

Question 15

Human cells contain

Answer 15

46 chromosomes, which are in pairs. Sex cells (sperm and ova) contain only 23 chromosomes. The 23 chromosomes comprise one from each pair.

Question 16

Of the 23 pairs of chromosomes present is each human cell, one pair is

Answer 16

the sex chromosomes. These determine the sex of the individual. Male have XY, female have XX. So the presence of a Y chromosome results in male features developing.

Question 17

DNA

Answer 17

Each chromosome contains one very long molecule of DNA. The DNA molecule carries a code that instructs the cell about which kind of proteins it should make. Each chromosome carries instructions for making many different proteins.

Question 18

Gene

Answer 18

Each chromosome is made up of a large number of genes coding for the formation of different proteins which give us our characteristics. The gene responsible for a particular characteristic is always on the same relative position on the chromosome.

Question 19

Alleles

Answer 19

When the chromosomes are in pairs, there may be a different form (allele) of the gene on each chromosome.

Question 20

mitosis

Answer 20

Mitosis is a nuclear division giving rise to genetically identical cells in which the chromosome number is maintained by the exact duplication of chromosome.

Question 21

Meiosis

Answer 21

Meiosis is a reduction division in which the chromosome number is halved from diploid to haploid.

Question 22

Mitosis is the way in which any cell (plant or animal) divides when an organism is

Answer 22

growing
repairing a damaged part of its body
replacing worn out cells

Question 23

Growth means

Answer 23

getting bigger. An individual cell can grow a certain amount, but not indefinitely. Once a cell gets to a certain size, it becomes difficult for all parts of the cell to obtain oxygen and nutrients by division. In order to grow any more, the cell divides to form two smaller cells, each of which can then grow and divide again.

Question 24

Mitosis is also used in

Answer 24

asexual reproduction

Question 25

Process of mitosis

Answer 25

During the process, all the chromosomes in the parent cell are copied. Each copy remains attached to the original one --> each chromosome is made up of 2 identical threads joined together. The parent cell (with 4 chromosomes) split to form 2 nuclei each with 2 chromosomes as the parent nucleus cell. At the end of a mitotic cell division, the number of cells is doubled and the daughter cells produced are genetically identical to the parent.

Question 26

Meiosis

Answer 26

Meiosis is the way in which gametes (sex cells) are produced. Gametes have only half the number of chromosome of a normal body cell. They have 1 set of chromosome instead of 2. When they fuse together, the zygote formed has 2 sets. Human gametes are formed by the division of cells in the ovaries and testes The gametes produced are haploid, but they are formed from diploid cells, so meiosis involves halving the normal chromosome number - the pairs of chromosomes are separated. During meiosis, the new cells get a mixture of homologous chromosomes from father and mother --> A sperm cell could contain a chromosome 1 from father and a chromosome 2 from mother. There are all sorts of combinations --> gametes are genetically different form the parent cells. Meiosis produces genetic variation. When ova are formed in a woman, all the ova will carry an X chromosome. When sperm are formed in a man, half the sperm will carry an X chromosome, half will carry a Y chromosome.

Question 27

monohybrid cross

Answer 27

A monohybrid cross involves the crossing of individuals and the examination of one (mono) character (flower colour, pod shape...) and different (hybrid) traits (red colour, white colour) in their offspring.

Question 28

codominance

Answer 28

Sometimes, neither of a pair of alleles is completely dominant or completely recessive. Instead of one of them completely hiding the effect of the other in a heterozygote, they both have an effect on the phenotype. This is called codominance