B6

Question 1

1. What is a gamete?

Answer 1

A cell with half the number of chromosomes of the parent cell.

Question 2

2. Name the male and female gametes in a) a human b) a daisy plant

Answer 2

a) Male = sperm Female = egg

b) Male = pollen Female = egg

Question 3

meiosis

Answer 3

Genetic mixing happens
Gamete production occurs
New cells show variation
Two divisions occur

Question 4

mitosis

Answer 4

New cells have same no. of chromosomes as parent
Happens in skin cells
Two new cells are formed as a result
Identical cells are formed

Question 5

4. How many chromosomes are found in the nucleus of a human:
   a) ovary cell ?
   b) egg cell ?
   c) embryo cell ?
   d) a cell just after fertilisation has occurred?
   e) a testes cell ?

Answer 5

a) ovary cell ? 46
b) egg cell ? 23
c) embryo cell ? 46
d) a cell just after fertilisation has occurred? 46
e) a testes cell ? 46

Question 6

5. Name the shape which best describes the DNA polymer.

Answer 6

double helix

Question 7

6. How is DNA organised inside the cell nucleus?

Answer 7

arranged in chromosomes

Question 8

7. Which is larger, a chromosome or a gene?

Answer 8

chromosome

Question 9

8. What does a gene code for?

Answer 9

a particular sequence of amino acids

Question 10

9. Write down the definition of the genome of a horse.

.

Answer 10

all the genetic material of the horse `

Question 11

10. List two reasons why it is important to understand more about the
    human genome

Answer 11

To be able to identify the genes which are linked to different diseases
To understand and be able to treat inherited disorders
To use in tracing human migration patterns from the past.

Question 12

11. What are three advantages of sexual reproduction?

Answer 12

Produce variation in the offspring
If environment changes can give a survival advantage meaning some organisms
are likely to survive
Humans can speed up natural selection by selective breeding to increase food
production

Question 13

12. What are three advantages of asexual reproduction?

Answer 13

Only one parent needed
More time and energy efficient as do not need to find a mate
Faster than sexual reproduction
Many identical offspring can be produced when conditions are favourable

Question 14

13. List three organisms which reproduce using both sexual and asexual reproduction
    methods.

Answer 14

Malarial parasites
Fungi
Strawberry plants
Daffodils

Question 15

14. Where would you find a nucleotide?

Answer 15

DNA

Question 16

15. What does a nucleotide consist of?

Answer 16

Common sugar, phosphate group, base

Question 17

16. What are the symbols of the 4 bases found in DNA?

Answer 17

A
T
C
G

Question 18

17. What does the code for an amino acid consist of?

Answer 18

A sequence of three bases

Question 19

18. Fill in the missing terms:
    The long strands of DNA are made of alternating _____ and ______ sections.
    Attached to each ______ is one of the four bases.
    The DNA polymer is made up of repeating ____________ units.

Answer 19

The long strands of DNA are made of alternating __sugar___ and __phosphate____
sections.
Attached to each __sugar____ is one of the four bases.
The DNA polymer is made up of repeating _____nucleotide_______ units.

Question 20

19. In the complementary strands of DNA – which base is T always linked to?

Answer 20

A

Question 21

20. Which organelle in the cytoplasm carries out protein synthesis?

Answer 21

ribosomes

Question 22

21. What do carrier molecules bring to the organelle from the cytoplasm?

Answer 22

amino aicd

Question 23

21. What happens in protein synthesis once the protein chain is complete?

Answer 23

The protein folds

up into a unique shape.

Question 24

22. What happens if a mutation codes for a slightly altered enzyme protein with a different
    shape?

Answer 24

The enzyme may no longer fit the substrate binding site

Question 25

23. What can non-coding parts of DNA do?

Answer 25

Switch genes on or off and affect how genes are | expressed

Question 26

1. Complete the sentences below using one of the following words: genotype phenotype homozygous gamete chromosome The same alleles for a particular characteristic are described as .......................... Mice fur can be described by its colour. This is known as the ............................... The alleles for a particular characteristic determine its ........................................ The pollen of a rose plant can also be described as a male ..................................

Answer 26

The same alleles for a particular characteristic are described as homozygous Mice fur can be described by its colour. This is known as the phenotype The alleles for a particular characteristic determine its genotype The pollen of a rose plant can also be described as a male gamete

Question 27

2. What are the different forms of a gene called ?

Answer 27

alleles

Question 28

3. Why is it easy to describe an organisms phenotype for a particular characteristic but very difficult to state the genotype?

Answer 28

Most characteristics are a result of multiple genes interacting

Question 29

4. List the alternative ways of describing the following outcome of a genetic cross: 3 in every 4 crosses will have black fur.

Answer 29

75% 0.75 3/4

Question 30

5. If two heterozygous tall plants were crossed 75 times, what proportion of the offspring would you expect to be short?

Answer 30

25% or 19

Question 31

6. What is polydactyly and is it caused by inheriting a recessive or dominant allele?

Answer 31

A genetic disorder which results in having extra fingers or toes - dominant allele

Question 32

9. Black fur is dominant to brown fur in mice. Use B to represent black fur and b to represent brown fur. a) Complete the Punnett square diagram to show the outcome of a genetic cross between two heterozygous mice. b) What is the phenotype of the parent mice? c) What are the chances of a homozygous recessive mouse being born to two heterozygous mice?

Answer 32

a) Gamete | B | b B | BB | Bb b | Bb | bb b) black fur c) 25%

Question 33

Is someone who is heterozygous for cystic fibrosis healthy?

Answer 33

Yes, they are a carrier but do not suffer from CF themselves

Question 34

e) Many people feel opposed to the screening of embryos to identify the CF allele. Suggest two reasons why they may feel this way.

Answer 34

Screening procedure may cause miscarriage or damage embryo/fetus The embryo has a right to life Screening is expensive and could be used for other purposes Have to make moral/ethical or religious decisions as a result such as whether to terminate

Question 35

12. The flower colour for pea plants is controlled by a single gene. Red flowers are dominant to white flowers. A homozygous dominant plant and a heterozygous plant are crossed to produce offspring. a) What is the phenotype of the homozygous dominant plant? b) Draw a genetic diagram to show all the possible arrangements of alleles in the offspring. c) What is the chance of producing homozygous dominant red flowering plants?

Answer 35

a) red flowers b) Gamete | R | r R | RR | Rr R | RR | Rr c) 1 in 2 or 50%