Genetics

Question 0

DNA Structure

Answer 0

• double helix - formed from 2 separate strands which are coiled together forming a spiral
• polynucleotides

Question 1

DNA Function

Answer 1

Contains genetic information that has all the information needed to grow and develop from a fertilised egg

Question 2

Nucleotide Structure

Answer 2

• phosphate group, a nitrogen base and a pentode sugar which is deoxyribose
• 4 possible bases (A,T,C,G)

Question 3

Polynucleotide strands

Answer 3

• join between phosphate group and a sugar

* forms a sugar-phosphate backbone

Question 4

Specific base pairing

Answer 4

• join together by hydrogen bonds
• adenine with thymine
• guanine with cytosine

Question 5

Structure vs function

Answer 5

• double helix structure makes it stable in cell and isn’t easily damaged/broken down
• coiled up tightly allows a lot of information to fit in a small space
• paired structure makes is easier to copy itself (semi-conservative replication)

Question 6

DNA storage - eukaryotic cells

Answer 6

• linear
• really long
• wound around proteins (histones)
• coiled up tightly

Question 7

DNA storage - prokaryotic cells

Answer 7

• shorter and circular
• isn’t wound around proteins
• supercoiling
• free floating

Question 8

What are genes?

Answer 8

*sections of DNA found on chromosomes that code for polypeptides

Question 9

Making proteins using genes

Answer 9

• the order of nucleotide bases in a gene determines the order of amino acids, coded by a sequence of 3 bases
• degenerate - more than 1 base triplet can code for the same amino acid

Question 10

Non-coding DNA

Answer 10

• genes in eukaryotic DNA contain sections that don’t code for amino acids (intons) which is removed during protein synthesis
• eukaryotic cells contain regions of multiple repeats which don’t code for amino acids

Question 11

Genes and development

Answer 11

*enzymes speed up our metabolic pathways so contribute to our development and our phenotype

Question 12

What are alleles?

Answer 12

• a different version of a gene
• order of bases is slightly different so code for slightly different versions of the same characteristic
• found at same position (locus)

Question 13

Homologous chromosomes

Answer 13

• 23 pairs

* same size and have the same genes, but can have different alleles

Question 14

Gene mutations

Answer 14

• changes in the base sequence
• can produce new alleles of genes which could be non-functional
• mutation can cause enzymes to not fold properly producing an active site that’s the wrong size

Question 15

Gametes and fertilisation

Answer 15

• gametes join to form a zygote which divides and develops into new organism
• normal body calls have a diploid number of chromosomes
• gametes have a haploid number of chromosomes

Question 16

Meiosis

Answer 16

• 1- DNA unravels and replicates so there are 2 copies of each chromosome, called chromatids
• 2- DNA condenses to form double-armed chromosomes, made from 2 sister chromatids
• 3- chromosomes arrange into homologous pairs
• 4- first division: pairs separated, halving number of chromosomes
• 5- second division: sister chromatids are separated
• 6- 4 haploid cells that are genetically different are produced

Question 17

Creating genetic variation in gametes

Answer 17

• 1- crossing over of chromatids

* 2- independent segregation of chromosomes

Question 18

What is genetic diversity?

Answer 18

• variety in DNA
• different species have different genes
• alleles create it

Question 19

Factors that increase genetic diversity

Answer 19

• mutation in DNA - forming new alleles

* gene flow - different alleles moving between populations

Question 20

Factors that decrease genetic diversity

Answer 20

• genetic bottlenecks
• the founder effect
• selective breeding

Question 21

Genetic bottlenecks

Answer 21

• event causing a big reduction in a population

* reduces number of different alleles in a gene pool

Question 22

The founder effect

Answer 22

• describes just a few organisms from a population starting a new colony
• smaller number of alleles in the gene pool
• increased inbreeding which can lead to higher incidence of genetic disease

Question 23

Selective breeding

Answer 23

*humans selecting which domesticated animals/strains of plants to reproduce together to produce useful characteristics

Question 24

Arguments for selective breeding

Answer 24

• produces high yielding animals/plants
• increased resistance to disease so fewer drugs are needed
• bred to have increased tolerance of bad conditions

Question 25

Arguments against selective breeding

Answer 25

• can cause health problems

* reduces genetic diversity