reproduction, genome and gene expression

Question 1

what is meiosis?

Answer 1

sexual reproduction, where the genetic information from two organisms (the father and the mother) are combined to produce offspring that is genetically different to either parent

Question 2

what is a gamete?

Answer 2

a sex cell

Question 3

what is the female gamete and male gamete

Answer 3

egg cell - female
sperm cell - male

Question 4

why do gametes have haploid nuclei?

Answer 4

At fertilisation, the 23 chromosomes from each gamete combine to make 46 chromosomes. It ensures the offspring has the right amount of DNA.

Question 5

What is the technical term for a fertilised egg?

Answer 5

a zygote

Question 6

describe the process of meiosis

Answer 6

• before the cell divides, the DNA is duplicated
• the chromosome pairs line up in the centre of the cell, before being pulled apart
• this means that the cell has only one copy of each chromosome
• in the second division, the chromosomes line up again so the chromatids can be pulled apart
• this results in 4 genetically different haploid daughter cells

Question 7

what are the advantages of sexual reproduction

Answer 7

• creates genetic variation as every organism has inherited different genes from their parents
• this means that if environmental conditions change, it is more likely that more organisms have the characteristics to survive
• over time, this leads to natural selection and evolution

Question 8

what are the disadvantages of sexual reproduction

Answer 8

• takes more time and energy, so fewer offspring are birthed in a lifetime
• need to find a mate

Question 9

what are the advantages of asexual reproduction

Answer 9

• only one parent is needed, no need to find a mate
• the reproductive cycle is very fast, lots of offspring are produced quickly

Question 10

what are the disadvantages of asexual reproduction

Answer 10

• all the offspring will be genetically identical
• this means that if the conditions in the environment change and become unfavourable, it could affect an entire population

Question 11

what is the full name of DNA

Answer 11

deoxyribonucleic acid

Question 12

describe the shape of DNA

Answer 12

two strands twisted together to make a double helix shape

Question 13

what is a nucleotide

Answer 13

a repeating unit of DNA, includes a sugar, phosphate and base

Question 14

what are the 4 bases

Answer 14

A (adenine)
C (cytosine)
T (thymine)
G (guanine)

Question 15

what are the complementary base pairs

Answer 15

a - t
c - g
held by weak hydrogen (covalent) bonds

Question 16

what is a gene

Answer 16

a section of DNA which codes for a particular protein

Question 17

what is a chromosome

Answer 17

a long, coiled up molecule of DNA which carries genes

Question 18

define genome

Answer 18

combination of all the DNA in an organism

Question 19

describe how to extract DNA from fruit

Answer 19

• crush strawberries and put them into a solution containing detergent and salt
  detergent = breaks down cell membranes
  salt = makes DNA stick together
• filter mixture so froth is removed
• add ice cold ethanol to the mixture, DNA is insoluble in ethanol, so it lies at the top as a stringy, white precipitate

Question 20

what is a mutation

Answer 20

• rare random change to an organism’s DNA sequence
• if a mutation affects a gene, it produces an allele which may code for a different sequence of amino acids
• this can change the shape of the final protein and its activity