B6 - Inheritance, variation and Evolution

Question 1

Describe the differences between sexual and asexual reproduction

Answer 1

Sexual reproduction - The fusion of male and female gametes (genetic information from both male and female parent)

Asexual reproduction - Only 1 parent (offspring are genetically identical/ clones)

Question 2

Describe how meiosis halves the number of chromosomes in gametes

Answer 2

1. The chromosomes are copied
2. The cell divides into 2
3. Both of these cells divide one more time, forming the gametes (single chromosomes)

Question 3

Describe how fertilisation restores the full number of chromosomes

Answer 3

The gametes join together to form pairs of chromosomes through sexual reproduction

Question 4

What are the advantages of sexual reproduction?

Answer 4

Sexual reproduction produces variation in the offspring, meaning some of the offspring may survive if the environment changes.
It gives a species a greater chance of survival if conditions become challenging.

Selective breeding produces a high yield of good-quality offspring.

Question 5

What are the advantages of asexual reproduction?

Answer 5

Only one parent is needed, meaning it is more efficient in both time and energy as there is no need to find a mate.

It is extremely useful when conditions are favourable as an organism can produce many genetically identical offspring rapidly

Question 6

What are the disadvantages of asexual reproduction?

Answer 6

It is very risky - because all the offspring are genetically identical, there is a risk they could all die if conditions become unfavourable

Question 7

What are the disadvantages of sexual reproduction?

Answer 7

It takes time and energy to find a mate.

It is not possible for an isolated individual to reproduce

Question 8

Compare meiosis and mitosis

Answer 8

Meiosis includes two nuclear divisions which produce non-identical daughter cells. Each daughter cell contains one set of chromosomes.

Mitosis includes one nuclear division that produces two identical daughter cells. Each daughter cell contains two full sets of chromosomes.

Question 9

What are the names of the male and female gametes in:
1) Plants
2) Animals

Answer 9

1) Pollen cells and egg cells

2) Sperm cells and egg cells

Question 10

What is asexual reproduction?

Answer 10

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

Question 11

Describe how three different organisms reproduce both sexually and asexually:
1) Malarial Parasites
2) Fungi
3) Plants

Answer 11

1) Malarial parasites reproduce asexually in the human host and sexually in the mosquito.

2) Fungi reproduce asexually by spores, but also reproduce sexually to give variation.

3) Plants reproduce sexually, but some also reproduce asexually. Strawberry plants reproduce asexually via runners; daffodils reproduce asexually via bulb division.

Question 12

Describe the structure of DNA

Answer 12

DNA is a polymer made up of two strands of nucleotides that are twisted to form a double helix.

Question 13

Describe how protein synthesis occurs

Answer 13

A template is made of the DNA.
The template moves from the nucleus to the cytoplasm of the cell where it attaches to a ribosome.
A carrier molecule attaches to every three bases of the template.
The carrier molecule is attached to an amino acid.
The amino acids are joined together to form a chain.
The chain folds into the final shape of the protein.

Question 14

What effect might a mutation in a non-coding region of DNA have?

Answer 14

It might change the expression of a gene

Question 15

Define Genome

Answer 15

The entire genetic material of an organism

Question 16

Define Gamete

Answer 16

The sex cells which contain one set of genetic information

Question 17

Define chromosome

Answer 17

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

Question 18

Define Gene

Answer 18

A section of DNA that codes for a particular sequence of amino acids which makes a specific protein

Question 19

Define allele

Answer 19

A different form or variant of a gene

Question 20

Define dominant

Answer 20

Controls the characteristic, even if it is only present on one chromosome

Question 21

Define recessive

Answer 21

Only controls the physical characteristic if it is present on both chromosomes

Question 22

Define Homozygous

Answer 22

Two identical alleles for a characteristic

Question 23

Define heterozygous

Answer 23

Different alleles for a characteristic

Question 24

Define genotype

Answer 24

The alleles present in an individual for a particular characteristic

Question 25

Define phenotype

Answer 25

The physical appearance of an individual for a particular characteristic

Question 26

Explain why it’s important for us to study the human genome

Answer 26

It helps us to search for genes that are linked to different types of diseases. Understanding inherited disorders gives us more chance of repairing the genes or producing successful medicines. It also helps us to trace the migration patterns of humans from the past to develop a greater understanding of human evolution.

Question 27

What is the evolution script? (E.g. for Ducks)

Answer 27

There is variation in the population of ducks due to random mutations. Ducks with webbed feet can compete to swim faster and get more food. Therefore they are more likely to survive, reproduce and pass on the genes for webbed feet.

Question 28

What is meant by complementary strands?

Answer 28

The same bases always pair on the opposite strands. A - T G - C

Question 29

A change to a base is a…

Answer 29

Mutation

Question 30

What happens if mutations code for an altered protein with a different shape?

Answer 30

An enzyme may no longer fit the substrate binding site or a structural protein may lose its strength.

Question 31

Describe the inherited disorder cystic fibrosis

Answer 31

• A disorder of cell membranes. • Controlled by a single gene. • Two alleles - allele for defective cell membranes is recessive

Question 32

Describe the inherited disorder polydactyly

Answer 32

• Having extra fingers or toes • Dominant allele • Cannot be a carrier of the allele - true of any dominant allele

Question 33

Describe the issues around embryo screening

Answer 33

• Expensive - some think that the money should be spent elsewhere in the health service. • Some healthy embryos destroyed - unethical. • Producing offspring with desirable features is seen as unethical.

Question 34

Human body cells contain (..) of chromosomes

Answer 34

23 pairs

Question 35

How many pairs control characteristics only & how many pairs carry the genes that determine sex?

Answer 35

• 22 pairs control characteristics only • 1 pair carries the genes that determine sex

Question 36

Female sex chromosomes are:

Answer 36

XX

Question 37

Male sex chromosomes are:

Answer 37

XY

Question 38

Describe the causes of variation

Answer 38

• the genes they have inherited (genetic causes • the conditions in which they have developed (environmental causes) • a combination of genes & the environment