B13 - Reproduction

Question 1

Compare meiosis and mitosis

Answer 1

• Meiosis involves two nuclear divisions which produce 4 non-identical daughter cells. Each daughter cell contains one set of chromosomes (23).
• Mitosis involves one nuclear division that produces 2 identical daughter cells. Each daughter cell contains 2 full sets of chromosomes (46).

Question 2

What are the names of male and female gametes in both plants and animals?

Answer 2

• Plants: pollen and egg cells

- Animals: Sperm and egg cells

Question 3

What is asexual reproduction?

Answer 3

When there is only one parent and no fusion of gametes.
Only mitosis is involved, so there is no variation.
The offspring are genetically identical (clones).

Question 4

What is sexual reproduction?

Answer 4

When there are two parents and fusion of gametes to form a zygote.
Gametes are formed by meiosis, variation is introduced
Offspring are genetically different.

Question 5

How does fertilisation restore the correct number of chromosomes in a new cell body?

Answer 5

Fusion of gametes, each with 23 chromosomes, results in a total of 46 chromosomes in the new zygote.

Question 6

Fill in the gaps: A ___ is the entire ___ material of an ___.

Answer 6

• genome
• genetic
• organism

Question 7

What is a gamete?

Answer 7

A sex cell (sperm and/or egg cells), which contain one set of genetic information.

Question 8

What is a chromosome?

Answer 8

Found in the nucleus, they are made from long DNA molecules and passed from parent to offspring.

Question 9

True or False: a gene is a section of DNA that codes for a particular sequence of amino acids, to make a specific protein?

Answer 9

True.

Question 10

What is an allele?

Answer 10

A different form or variant of a gene

Question 11

What does dominant and recessive mean in terms of alleles?

Answer 11

• Dominant: Controls the characteristic, even if it is only present on one chromosome.
• Recessive: Only controls the physical characteristic if it is present on both chromosomes.

Question 12

True or False: homozygous means having different alleles for a characteristic?

Answer 12

False:

• Homozygous: two identical alleles for a characteristic.
• Hetrozygous: different alleles for a characteristic.

Question 13

List the parts of a DNA nucleotide.

Answer 13

• One sugar molecule
• One phosphate molecule
• One ‘base’

Question 14

How many bases in a DNA sequence code for one amino acid? What are the names of these bases?

Answer 14

• Three bases code for one amino acid

- These are: A, T, C and G

Question 15

Explain how mutations can lead to a change in the protein coded for by a gene.

Answer 15

• Mutations change the sequence of DNA bases in a gene
• Combination of three bases is different due to mutation
• A different amino acids made
• Different protein made
  (doesn’t always affect protein because there are many combinations of AAs for the same protein)

Question 16

True or False: “Most mutations have little or no effect on the protein coded for by a gene”

Answer 16

• True. Some will change it to such a small extent that its function or appearance is unaffected.

Question 17

How does variation in a population increase the chance of surviving environmental change?

Answer 17

=> Some individuals have characteristics that make them better suited to their environment (natural selection)
=> More likely to survive environmental change and reproduce
=> Offspring inherit these genes
=> Population grows with more that are more likely to survive environmental change.

Question 18

Describe the methods of asexual and sexual reproduction used by strawberry plants.

Answer 18

=> Seeds produced using SEXUAL reproduction

=> Runners using ASEXUAL reproduction grow horizontally along surface of soil away from plant

Question 19

What is the probability that offspring will have the XX combination of sex chromosomes? What gender will the offspring be?

Answer 19

• 50% chance of XX (female)

- 50% chance of XY (male)

Question 20

How many genes are responsible for controlling fur colour in mice?

Answer 20

• A single gene

Question 21

What is the chance of a child being born with polydactyly if one parent has a single dominant allele for the gene that controls it?

Answer 21

• 50% (Pp) (has polydactyly)

- 50% (pp) (doesn’t have polydactyly)

Question 22

Give two arguments for and two arguments against screening embryos for genetic disorders.

Answer 22

FOR:
- Help stop suffering
- Treating disorders costs Gov. money - no more treatments
- Laws that stop it going too far
AGAINST:
- Implies people with genetic disorders are ‘undesirable’ (increases prejudice)
- Screening is expensive

Question 23

Explain how protein synthesis works.

Answer 23

=> mRNA formed by copying code from DNA strand
=> mRNA leaves nucleus into cytoplasm
=> mRNA binds to surface of ribosome
=> In cytoplasm, tRNA attached to specific AAs joins to mRNA in correct order (reads code of bases)
=> Amino acids joined to form specific protein
=> Completed protein chain folds up into unique shape (e.g. enzyme).