17) Inheritance (4.11)

Question 1

1.1. What are chromosomes made of?

Answer 1

DNA, which contains genetic information in the form of genes

Question 2

1.2. Define a gene

Answer 2

A length of DNA that codes for a protein

Question 3

1.3. Define an allele

Answer 3

An alternative form of a gene

Question 4

1.4. Describe the inheritance of sex in humans with reference to X and Y chromosomes

Answer 4

Sex is determined by a chromosome pair (most other characteristics are just determined by one or a number of genes)

AFABs have XX and AMABS have XY

Half (125 million) of the sperm will be carrying the X chromosome, and the other half carries the Y chromosome, so the father is responsible for determining the gender of the offspring

All egg cells carry an X chromosome

Question 5

1.5. What determines the sequence of amino acids used to make a specific protein

Answer 5

The sequence of bases in a gene

Question 6

1.6. What gives different shapes to protein molecules?

Answer 6

Different sequences of amino acids give different shapes to protein molecules

Question 7

1.7. Explain how DNA controls cell function

Answer 7

By controlling the production of proteins, including enzymes, membrane carriers and receptors for neurotransmitters

Question 8

1.8. Explain how a protein is made

Answer 8

(a) The gene coding for the protein remains in the nucleus
(b) Messenger RNA (mRNA) is a copy of a gene
(c) mRNA molecules are made in the nucleus and move to the cytoplasm
(d) The mRNA passes through ribosomes, which read the code in groups of three
(e) The ribosome assembles amino acids into protein molecules
(f) The specific sequence of amino acids is determined by the sequence of bases in the mRNA

Question 9

1.9. Why are some genes not expressed?

Answer 9

Most body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs

Question 10

1.10. Describe a haploid nucleus

Answer 10

A nucleus containing a single set of chromosomes

Question 11

1.11. Describe a diploid nucleus

Answer 11

A nucleus containing two sets of chromosomes

Question 12

1.12. How many chromosomes are there in a diploid cell?

Answer 12

A pair of each type of chromosome and in a human diploid cell there are 23 pairs

Question 13

2.1. Describe mitosis

Answer 13

Nuclear division giving rise to genetically identical cells

Question 14

2.2. State the role of mitosis

Answer 14

Growth, repair of damaged tissues, replacement of cells and asexual reproduction

Question 15

2.3. When does the exact replication of chromosomes occur?

Answer 15

Before mitosis

Question 16

2.4. What happens during mitosis?

Answer 16

The copies of chromosomes separate, maintaining the chromosome number in each daughter cell

Question 17

2.5. Describe stem cells

Answer 17

Unspecialised cells divide by mitosis to produce daughter cells that can become specialised for specific functions

Question 18

3.1. What is meiosis involved in?

Answer 18

The production of gametes

Question 19

3.1. What is meiosis involved in?

Answer 19

The production of gametes

Question 20

3.2. Describe meiosis

Answer 20

A reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells

Question 21

4.1. Describe inheritance

Answer 21

The transmission of genetic information from generation to generation

Question 22

4.2. Describe genotype

Answer 22

The genetic make-up of an organism and in terms of the alleles present

Question 23

4.3. Describe phenotype

Answer 23

The observable features of an organism

Question 24

4.4. Describe homozygous

Answer 24

Having two identical alleles of a particular gene

Question 25

4.5. What is pure-breeding?

Answer 25

Two identical homozygous individuals that breed together

Question 26

4.6. Describe heterozygous

Answer 26

Having two different alleles of a particular gene

Question 27

4.7. Can a heterozygous individual be pure-breeding?

Answer 27

No

Question 28

4.8. Describe a dominant allele

Answer 28

An allele that is expressed if it is present in the genotype

Question 29

4.9 Describe a recessive allele

Answer 29

An allele that is only expressed when there is no dominant allele of the gene present in the genotype

Question 30

4.11. Use genetic diagrams to predict the results of monohybrid crosses and calculate phenotypic ratios

Answer 30

Aa x aa = 1:1 ratio
Aa x Aa = 3:1 ratio

Question 31

4.13. Explain how to use a test cross to identify an unknown genotype

Answer 31

Crossing with a recessive is called a test cross (or back cross), which tells us if an unknown dominant phenotype is heterozygous or homozygous

Homozygous: all the offspring will have the dominant allele
Heterozygous: 1 : 1 ratio of dominant : recessive allele