Revision – Core Science Biology
ANSWERS
Complete the following activities from your Textbook.
Questions 1-3 page 157.
1. Genes are strands of DNA found in the chromosomes.
2. Humans have 23 pairs of chromosomes
3. A diploid cell contains 2 copies of every chromosome, while a
haploid cell has only 1 copy of each chromosome.
Questions 1-3 and 7 page 165
1. Dominant – an allele that affects the organisms traits even when
it ahs only one copy.
Recessive – an allele that affects the organisms traits only when it
has two copies.
Genotype – the genetic makeup of an organism
Phenotype- the appearance and function of an organism.
Homozygous – having two copies of the same allele
Heterozygous – having different alleles of a particular gene.
2. F, T, T
3. Dominant are represented by capital letters and recessive are
represented by lower case letters.
7. a) Round seed and yellow seeds are dominant
b) Round yellow seeds.
Questions 1-6 page 169
1. Male – square
Female – circle
Affected – shaded
Carrier – small c or half shaded
Not affected – left unshaded
Horizontal line – marriage
Vertical line – offspring
y
y
Y
Yy
Yy
Y
Yy
Yy
Genotype – Yy, phenotype all yellow seeds (4:4 chance)
Then complete the questions from this revision sheet.
1) What is the scientific term used to describe a person’s genetic information?
genotype
2) On the DNA molecule you see to your right label it using the following words:
1.
2.
3.
4.
5.
6.
7.
8.
Adenine
Guanine
Thymine
Cytosine
Sugar
Phosphate
Back bone
Base pair
In the diagram you need to match the Adenine
With the Thymine and the Cytosine with the
Guanine (then label either as base pair).
Ensure you have labelled the sugar as the red
And the phosphate as the white.
3) Where is the DNA stored in a cell?
In the chromosomes in the nucleus of the cell
DNA is stored in tightly coiled structures called chromosomes.
4) How many chromosomes in a human body cell?
46 individual or 23 pairs.
5) How many chromosomes in a gamete?
A gamete is a sex cell (i.e. sperm or egg) so it is haploid therefore 23 individual
chromosomes.
6) How many chromosomes in a human haploid cell?
23 individual chromosomes
7) Name a haploid cell.
Sperm or egg
Multiple Choice questions
Question 1
Which of the following is the genotype for a heterozygous individual?
1. TT
2. Tt
3. tt
4. Two different
Question 2
A punnet square is used to:
1. Store strawberries
2. Predict the phenotype of F1
3. Predict the genotype of offspring
4. Record genotypes
Question 3
Which of the following is the genotype for a homozygous recessive individual?
1. TT
2. Tt
3. tt
4. Two different
Question 4
Pure breeding means an individual is:
1. All white
2. Heterozygous
3. Homozygous
4. Has already been crossed
Question 5
What are the possible genotypes of offspring produced from a heterozygous cross? (tongue
rolling=T)
1. TT, tt, Tt
2. Tt, Tt, Tt, tt
3. TT, tt
4. TT, Tt, tt
Question 6
From the information, is tongue rolling a:
1. Recessive phenotype
2. Dominant phenotype
3. Heterozygous phenotype
4. A skill
Question 7
A gene is:
1. Is an allele
2. Is a section of DNA that codes for a protein
3. Aa
4. Is a dominant or recessive feature
BIOLOGY KEY WORD REVISION
Genetics The scientific study of heredity how particular qualities or traits are
transmitted from parents to offspring
Gene - A hereditary unit consisting of a sequence of DNA that occupies a specific
location on a chromosome and determines a particular characteristic in an organism.
Genes undergo mutation when their DNA sequence changes.
Inheritance - each organism’s chromosomes carry characteristics & attributes from
biological hereditary pathways from parents.
Heredity transmitted from parent to child by information contained in the genes
Nucleus part of the cell containing DNA and RNA and responsible for growth and
reproduction
chromosomes – the lengths of DNA that shorten and coil
chromatid -one of two identical chromosomal strands into which a chromosome splits
longitudinally preparatory to cell division
centromere – The central region of a chromosome that holds the two cromatids
together
autosome A chromosome that is not one of the sex chromosomes
sex chromosome an X or Y chromosome. The XX pair determines female, and the XY
pair determines male
diploid – the no. of chromosomes in each body cell is it’s diploid no. – 46 in humans
haploid – the haploid no. is half the number of chromosomes in a cell – 23 in humans
karyotype – the process of sorting chromosomes into their matched pairs.
Karyotyping is important in the study of chromosomal disorders
gamete - a mature sexual reproductive cell having a single set of unpaired
chromosomes
zygote - The cell formed by the union of two gametes
deoxyribonucleic acid A chain of nucleotides (cytosine, guanine, adenine, or thymine)
linked with ribose sugar molecules that form the basis of genetic material. Specific
patterns of nucleotides represent particular genes. It is also the substance of heretiry
traits.
double helix The twisted-ladder shape that two linear strands of DNA assume when
complementary nucleotides on opposing strands bond together
bases (A, T, C, G) The molecular building blocks of DNA and RNA: adenine, cytosine,
guanine, thymine, and (in RNA only) uracil. In DNA, A attaches only to T, and C attaches
only to G. In RNA, A attaches only to U, and C attaches only to G.
sugar phosphate backbone – the backbone of a DNA molecule that contains the A, T, C
and G coding.
Heterozygous-having 2 different alleles for a characteristic
Homozygous- Having identical alleles for a single trait.