inheritance

Question 1

Define chromosomes

Answer 1

Chromosomes are made of DNA; which contains genetic information * in the form of genes.

Question 2

Define gene

Answer 2

length of DNA
* that codes for a protein

Question 3

Define allele

Answer 3

alternative form of gene!

Question 4

what does sex determination depend on?

Answer 4

• All eggs have one X chromosome.
• However a sperm can have either X or Y chromosome.
• Therefore sex determination depends on whether the sperm that fertilizes the egg carries a Y or X chromosome.

Question 5

what determines the sequence of amino acids used to make a specific protein?

Answer 5

• sequences of bases in a gene
• different sequences of amino acids give different shapes to protein molecules

Question 6

How does DNA control cell function?

Answer 6

• controlling the production of proteins
  including enzymes, membrane carriers & receptors for neurotransmitters

Question 7

Explain how a protein is made

Answer 7

• the gene coding for the protein remains in the nucleus
• messenger RNA (mRNA) is a copy of a gene
• mRNA molecules are made in the nucleus and move to the cytoplasm
• the mRNA passes through ribosomes
• the ribosome assembles amino acids into protein molecules
• the specific sequence of amino acids is determined by the sequence of bases in the mRNA

Question 8

Are all proteins made in all cells?

Answer 8

no.
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 9

What’s a haploid nucleus?

Answer 9

nucleus containing a single set of chromosomes

Question 10

What’s a diploid nucleus?

Answer 10

nucleus containing two sets of chromosomes

i.e. all body cells except gametes
- One pair of each type of chromosome
- 23 pairs in a human

Question 11

define mitosis

Answer 11

nuclear division giving rise to
genetically identical cells

Question 12

role of mitosis

Answer 12

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

Question 13

How does mitosis occur?

Answer 13

Chromosomes replicate before mitosis occurs
- Copies of chromosomes separate
- Chromosome number is maintained in each daughter cell

Question 14

define stem cells

Answer 14

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

Question 15

define meiosis

Answer 15

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

Question 16

Role of meiosis

Answer 16

• involved in production of gametes
• takes place in testes/ovaries

Question 17

why is meiosis known as reductive division?

Answer 17

• Chromosome number is halved (from diploid to haploid)
• Results in genetically varied daughter cells
• New combinations of maternal and paternal genes made

Question 18

define inheritance

Answer 18

• the transmission of genetic information
• from generation to generation

Question 19

define genotype

Answer 19

• Genetic make-up of an organism
• i.e. which alleles are present in the organism’s genome

Question 20

define phenotype

Answer 20

observable features of an organism

Question 21

homozygous

Answer 21

• having 2 identical alleles of a particular gene

Question 22

what happens when 2 homozygous individuals?

Answer 22

it’ll be pure-breeding

Question 23

define heterozygous

Answer 23

having 2 different alleles of a particular gene

Question 24

define dominant allele

Answer 24

• an allele that is expressed
• if it is present in the genotype

Question 25

define recessive allele

Answer 25

• an allele that is only expressed
• when there’s no dominant allele
• of the gene present in the genotype

Question 26

what’s codominance

Answer 26

• situation in which both alleles in heterozygous organisms
• contribute to the phenotype

Question 27

Explain the inheritance of ABO blood groups

Answer 27

• phenotypes are A, B, AB and O blood groups
• alleles are IA, IB and Io

Question 28

What’s a sex linked characteristic

Answer 28

• a feature in which the gene responsible is located on a sex chromosome
• and that this makes the characteristic more common in one sex than in the other

Question 29

give an example of sex-linkage

Answer 29

• red-green colorblindness

Question 30

what’s test cross used for

Answer 30

• To identify the genotype of an organism showing the dominant phenotype

Question 31

hows test cross carried out

Answer 31

Cross the unknown individual with individual showing recessive phenotype
- Offspring either 50% dominant and 50% recessive OR all dominant
- If any offspring have recessive phenotype → unknown individual was heterozygous
- If no offspring have recessive phenotype → unknown individual was homozygous

Question 32

Why are sex-linked diseases usually associated with the X chromosome?

Answer 32

• Y chromosome is much shorter than the X chromosome
• Comparatively few genes exist on the shorter Y chromosome

Question 33

Why are X-linked dominant traits more common in females?

Answer 33

• Females have two X chromosomes = two alleles
• Either allele may be dominant and cause disease
• Can be either homozygous or heterozygous

Question 34

Why are X-linked dominant traits more common in males?

Answer 34

Males have only one X chromosome = one allele
- Condition cannot be masked by a second allele

Question 35

For sex-linked diseases:

Answer 35

• Only females can be carriers
• Males always inherit X-linked trait from mother
• Females cannot inherit X-linked recessive condition from unaffected father