SB3 Separate Content

Question 1

Define sexual reproduction

Answer 1

The process involving the fusion of the male and female gametes, each containing genetic information from the mother or the father

Question 2

What are the human gametes?

Answer 2

• sperm cells - male
• egg cells - female

Question 3

What are the plant gametes?

Answer 3

• pollen - male
• egg cell - female

Question 4

Describe a gamete

Answer 4

• haploid
• therefore contains 23 pairs
• produced through meiosis

Question 5

What are the advantages of sexual reproduction?

Answer 5

• increases sexual variation
• species can adapt to new environmentsdue to variation, giving them a survival advantage
• disease less likely to affect population (due to variation)

Question 6

What are the disadvantages of sexual reproduction?

Answer 6

• takes time and energy to find mates
• slow
• difficult for isolated members of a species to reproduce

Question 7

Define asexual reproduction

Answer 7

The process in which genetically identical offspring are being produced by one parent

Question 8

What are the advantages of asexual reproduction?

Answer 8

• no need to find a mate
• rapid reproductive cycle (if enough food available)
• If a parent is well adapted to the environment, offspring will be too

Question 9

What are the disadvantages of asexual reproduction?

Answer 9

• limited genetic variation in population
• population vulnerable to changes in habitat and may only be suitable to one habitat
• disease more likely to affect the whole population - could cause them to be wiped out

Question 10

What is a codon?

Answer 10

A sequence of three nucleotides (bases) in a DNA or RNA molecule that codes for an amino acid

Question 11

What determines the protein produced?

Answer 11

The order of bases

Question 12

What are the two stages in protein synthesis?

Answer 12

• transcription
• translation

Question 13

What happens in transcription?

Answer 13

• RNA polymerase attaches to DNA in front of a gene in the non-coding region and the two DNA strands separate
• RNA polymerase moves along the template strand and adds complimentary bases to form messenger RNA (mRNA)
• mRNA has the base uracil rather than T, which pairs with Adenine
• mRNA leaves nucleus through pores

Question 14

What are the proteins involved in transcription?

Answer 14

• mRNA
• RNA polymerase

Question 15

What base is present in protein synthesis that is not present in DNA?

Answer 15

Uracil (U)

Question 16

What does the base U bind with?

Answer 16

A

Question 17

What occurs in translation?

Answer 17

• mRNA attaches to ribosomes in the cytoplasm
• Ribosome moves along mRNA 3 bases at a time
• at each mRNA codon, a transfer RNA with complementary bases lines up
• it carries an amino acid
• Ribosomes moves along and the amino acid joins up to form a polypeptide
• empty tRNA leaves
• Amino acids join to form a polypeptide chain which folds to form a protein. Shape is important for function

Question 18

What are the proteins involved in translation?

Answer 18

• ribsome
• transfer RNA
• polypeptide

Question 19

Where does transcription occur?

Answer 19

In the nucleus

Question 20

Where does translation occur?

Answer 20

cyptoplasm

Question 21

How many different types of amino acids are there?

Answer 21

20

Question 22

Define genotype

Answer 22

Genes present in the DNA of an individual

Question 23

Define phenotype

Answer 23

Genes expressed in an individual: the visible effects of a genotype

Question 24

What are genetic variants?

Answer 24

Small changes in the order of bases that make up a strand of DNA

Question 25

What are the causes of genetic mutations ?

Answer 25

Mistakes when DNA is copied during cell division, or environmental factors such as radiation

Question 26

What is the effect of mutations in the **coding region** of DNA?

Answer 26

Will alter the structure or function of the protein produced because it will alter the **sequence of bases**

Question 27

What is the effect of mutations in the **non coding region** of DNA?

Answer 27

Affects the **binding of the RNA molecule**, which affects **how much of the protein is produced**

Question 28

How do mutations occur in the **non coding region** of DNA?

Answer 28

- RNA polymerase attaches to non-coding DNA found before genes - Mutations here may mean that it doesn't bind well (reducing transcription) - Mutations here may also cause it to bind better (increasing transcription) so more mRNA made

Question 29

What could be the effects of mutations in the sequence of bases in DNA?

Answer 29

- A base is **inserted** into a code - A base is **deleted** from a code - A base is **substituted** into a code - may not even change the amino acid, as several codons code for the same amino acid

Question 30

What are **stop codons**?

Answer 30

Codons that stop translation and don't code for an amino acid

Question 31

Who was Gregor Mendel?

Answer 31

The monk who started modern ideas about genes

Question 32

How did Gregor Mendel experiment?

Answer 32

Using pea plants

Question 33

What are the four blood groups?

Answer 33

- A - B - O - AB

Question 34

Which blood group is the universal donor?

Answer 34

Blood group O

Question 35

Which blood group is the universal receiver?

Answer 35

Blood group AB

Question 36

What are the alleles for deciding blood group?

Answer 36

I^A, I^B, I^O

Question 37

Which of the blood group alleles are dominant?

Answer 37

A and B

Question 38

Which blood group allele is recessive?

Answer 38

o

Question 39

What is codominance?

Answer 39

Blood group A and B are equally dominant, so they are both expressed, giving us blood group AB

Question 40

What is a **sex-linked disorder**?

Answer 40

Disorders caused by the XX and XY alleles

Question 41

Why are men more likely to have sex linked diseases?

Answer 41

- the Y gene is much smaller than the X - so the Y gene has less alleles than the X, and is even missing some alleles - therefore, if the X gene has a faulty allele, it will always be expressed **if the Y gene doesn't have the dominant counterpart**