9 - Inheritance (C2)

Question 1

What is the definition of a gene?

Answer 1

A sequence of DNA that codes for a polypeptide and which occupies a specific locus on a chromosome

Question 2

What is the definition of an allele?

Answer 2

A variant nucleotide sequence for a particular gene at a given locus, which codes for an altered phenotype

Question 3

What does homozygous mean?

Answer 3

The alleles of a particular gene are the same

Question 4

What does heterozygous mean?

Answer 4

The alleles of a particular gene are different

Question 5

What is the genotype of an individual?

Answer 5

The alleles that they contain

Question 6

What is the phenotype of an individual?

Answer 6

A description of their appearance, including characteristics that can’t be seen, e.g. their blood group

Question 7

What is a dominant allele?

Answer 7

An allele that has the same effect on the phenotype of a heterozygote as a homozygote

Question 8

What is a recessive allele?

Answer 8

An allele is only expressed when in a homozygous pair and when no dominant allele is present

Question 9

What is co-dominance?

Answer 9

When both alleles contribute to the phenotype

Question 10

What is monohybrid inheritance?

Answer 10

The inheritance of a single gene

Question 11

Why are peas useful to be used in inheritance experiments?

Answer 11

• They’re easy to grow
• Their flowers can self-fertilise and cross-fertilise
• They make flowers and fruit in the same year
• They make a large number of seeds from each cross

Question 12

Why did Mendel chose to study pairs of contrasting characteristics e.g. tall or dwarf plants?

Answer 12

• They’re controlled by single genes
• They’re controlled by genes on different chromosomes
• Easy to tell apart

Question 13

What is continuous variation?

Answer 13

Variation with a range of values that’s controlled by a number of genes e.g. height

Question 14

What is incomplete dominance?

Answer 14

When neither allele is dominant so the offspring phenotype is intermediate between that of the 2 homozygotes e.g. red flower + white flower -> pink flower

Question 15

What are linked genes?

Answer 15

Genes that are on the same chromosome and therefore are not separated at meiosis

Question 16

What increases the likelihood of crossing over of genes?

Answer 16

The further apart 2 genes are on a chromosome, the more opportunity there is for crossover to occur between them

Question 17

What number is the degrees of freedom?

Answer 17

1 less than the number of classes of data

Question 18

Why are the sex chromosomes called heterosomes?

Answer 18

Because they’re different sizes

Question 19

What are the autosomes?

Answer 19

The 22 pairs of identical genes in humans (non-sex chromosomes)

Question 20

What is a sex-linked gene?

Answer 20

A gene on the X chromosome that gives rise to a sex-linked condition

Question 21

What are 2 features of mutations?

Answer 21

• Spontaneous

- Random

Question 22

What is a mutation?

Answer 22

The change of the structure of a gene resulting in a variant form

Question 23

What mutations are inherited?

Answer 23

Only those that occur in gametes

Question 24

What can mutation rates be increased by?

Answer 24

• Ionising radiation

- Mutagenic chemicals e.g. those in cigarette smoke

Question 25

What can cause gene or point mutation?

Answer 25

DNA not being copied accurately in S phase

Question 26

What can cause chromosome mutation?

Answer 26

When chromosomes get damaged and they repair themselves incorrectly, altering their structure and affecting lots of genes

Question 27

What is aneuploidy and what causes it?

Answer 27

- Chromosome being lost or added - When chromosomes fail to separate to poles of dividing cells - Or when chromosomes fail to separate at anaphase 2

Question 28

What is polyploidy and what causes it?

Answer 28

Number of chromosomes doubling if the cell fails to divide following the first nuclear division after fertilisation

Question 29

Why are bacteria often used in mutation experiments?

Answer 29

They have: - Short life cycle - High rate of mutation

Question 30

What is non-disjunction?

Answer 30

When a faulty cell division in meiosis causes 1 of the daughter cells to receive 2 copies of the chromosome whilst the other receives none

Question 31

What are hermaphrodite organisms?

Answer 31

Those that produce both male and female gametes

Question 32

What is a carcinogen?

Answer 32

An agent that causes cancer

Question 33

What are tumour suppressor genes?

Answer 33

Genes that regulate mitosis and prevent cells dividing too quickly

Question 34

What is an oncogene?

Answer 34

A proto-oncogene with a mutation that results in cancer

Question 35

How can proto-oncogenes cause cancer?

Answer 35

Mutations can cause them to be switched on permanently causing rapid, repeated mitosis

Question 36

What is epigenetics?

Answer 36

The control of gene expression by modifying DNA or histones, but not by affecting the DNA nucleotide sequence

Question 37

What is the epigenetic modification of DNA methylation?

Answer 37

- Cytosine can have a methyl or hydroxymethyl group added | - Areas of DNA that are heavily methylated are less likely to be transcribed

Question 38

What is the epigenetic histone modification following translation?

Answer 38

- e.g. attaching an acetyl group to the amino acid lysine - These changes to histone proteins alter their interaction with DNA and changes the arrangement of the nucleosomes - Coiling is more relaxed and transcription factors and RNA polymerase have access to the DNA, so transcription is increased

Question 39

What is genomic imprinting?

Answer 39

If genes are activated into gametes, the inactivation may be transferred to the next generation

Question 40

When do you accept the null hypothesis in a chi squared test?

Answer 40

- If chi squared value < critical value - This means there's no sig diff between observed and expected - Accept null

Question 41

What is complete/total linkage?

Answer 41

- When 2 genes have their loci close together on the same chromosome so tend to occur in gametes in parental combinations - Causes 3:0:0:1

Question 42

What is the locus?

Answer 42

The position of a gene on a chromosome

Question 43

What is a benign tumour?

Answer 43

One that is not growing in size

Question 44

What is a malignant tumour?

Answer 44

A cancerous one

Question 45

What is a monohybrid cross?

Answer 45

A cross in which only one gene is being considered e.g. TT x tt

Question 46

What is a dihybrid cross?

Answer 46

A cross in which 2 genes are considered e.g. TTRR x ttrr