Genes and Alleles

Question 1

What is each chromatid made up of?

Answer 1

• 1 helical DNA molecule

Question 2

What is each DNA molecule made up of?

Answer 2

• a series of genes

Question 3

What is a gene?

Answer 3

• a section of DNA (series of nucleotides/bases) that controls a hereditary characteristic (trait)
• ie it is the basic unit of heredity in living organisms

Question 4

What do nearly all somatic cells have?

Answer 4

• an exact copy of all the genes in that organism

Question 5

Why does each cell contain 2 of each kind of gene (before replication)?

Answer 5

• because there are 2 of each kind of chromosome (paternal and maternal)

Question 6

What is a gene pool?

Answer 6

• the set of all genes, or genetic information, in a population of sexually reproducing organisms

Question 7

What does a large gene pool indicate?

Answer 7

• high genetic diversity
• increased chances of survival

Question 8

What does a small gene pool indicate?

Answer 8

• low genetic diversity
• increased possibility of extinction

Question 9

How active are genes?

Answer 9

• only the genes that are needed are activated and the other suppressed
• different genes are activated in different cells, creating the specific proteins that give a particular cell type its character (e.g. bone cells, brain cells, skin cells etc.)

Question 10

What are ‘housekeeping genes’?

Answer 10

• genes that are active in many types of cells, making proteins needed for basic functions

Question 11

What are hox genes?

Answer 11

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

Question 12

What are alleles responsible for?

Answer 12

• genes responsible for controlling different versions of a trait/characteristic found in the same locus on homologous chromosomes

Question 13

What is the control of genes called?

Answer 13

• epigenetics

Question 14

What are alleles?

Answer 14

• one of two or more forms of a gene

Question 15

How are alleles passed from parent to offspring?

Answer 15

• by way of chromosomes in the gametes that are made by the process of meiosis in the sex organs

Question 16

What happens to the gametes during fertilisation?

Answer 16

• a male gamete fuses with a female gamete to form a diploid zygote
• this divides by mitosis to form an entire new organism made up of cells
• each with the same set of chromosomes and alleles as in the zygote

Question 17

What is a genotype?

Answer 17

• a genotype is made up of all the genes an organism carries on its chromosomes which it has inherited from its parents

Question 18

What is a phenotype?

Answer 18

• the physical appearance of an organism
• partly programmed by genes, its genotype, and also external factors such as exercise, diet and environment

Question 19

When is an organism homozygous for a particular trait?

Answer 19

• if the pair of alleles at a locus are the same

Question 20

When is an organism heterozygous for a particular trait?

Answer 20

• if the pair of alleles at a locus are different

Question 21

What are the kind of alleles in a heterozygous pairing?

Answer 21

• dominant
• recessive

Question 22

What is a dominant allele?

Answer 22

• the trait that is expressed in the offspring

Question 23

What is a recessive allele?

Answer 23

• the trait that is suppressed in the presence of the dominant allele and not expressed in the offspring