Genes

Question 1

Describe the central dogma

Answer 1

DNA - mRNA - Protein

Question 2

What are the 2 components of chromosomes?

Answer 2

DNA and his tones (the protein that DNA wraps around)

Question 3

What is a locus?

Answer 3

The specific position of a specific gene on a chromosome

Question 4

How is a gene sequence read and transcribed?

Answer 4

Read in 3 letter groups called codons. The ribosome converts codons to amino acids

Question 5

Define virus.

Answer 5

An intracellular infectious agent

Question 6

Why do viruses need a host cell?

Answer 6

Need energy from the host cell as the virus cannot carry out its own metabolic pathway

Question 7

What are the 2 types of virus replication?

Answer 7

1. Lytic - impatient. Virus replicates immediately, eventually causing the cell to burst, killing it - then moving on to other host cells to repeat the process
2. Lysogenic - dormant (provirus) - waits to replicate. Viral genome becomes a part of the cell genome and continues to replicate as the cell replicates. Something happens, e.g. UV exposure, and the cell’s DNA becomes damaged. The cell then repairs it’s DNA, cutting the virus out of the genome in the process. The virus is then activated, and follows lytic replication cycle.

Question 8

Describe the components of an operon (3)

Answer 8

• promoter = DNA sequence recognised by RNA polymerase, which initialises transcription
• operator (on/off switch) = regulatory protein binds to a DNA sequence which can interfere with the activity of the polymerase, turning it on or off
• genes for proteins that work together = a sequence of related genes following the promoter and operator

Question 9

What is chromatin regulation?

Answer 9

Structure of chromatin can be relaxed, making the gene more accessible for transcription

Question 10

What is transcriptional regulation?

Answer 10

The way in which cells regulate the transcription of DNA to RNA, thereby controlling gene activity

Question 11

What are the different levels of transcriptional regulation?

Answer 11

1. Basal promoter - initiates transcription, located near the 5’ end
2. Distal promoter - enhances transcription, only about 10 bp long

Question 12

What is homeotic genes and what are the results of homeotic mutations?

Answer 12

Homeotic genes are responsible for the anatomical development of an organism. If mutated, one body part could be replaced by another

Question 13

What is homebox?

Answer 13

A DNA sequence found within homeotic genes

Question 14

What is the purpose of sexual reproduction?

Answer 14

To create genetic variability

Question 15

What are the 2 different stages of meiosis?

Answer 15

Meiosis I and meiosis II

1. From diploid to haploid - reduction of chromosomes
2. Further separation of chromosomes. Create 4 haploid gametes from the original 1 diploid cell

Question 16

What are the similarities between meiosis 1 and 2?

Answer 16

Both follow the same steps

Prophase - metaphase - anaphase - telophase

Question 17

Explain 1 of Mendels principles.

Answer 17

• dominance: resultant phenotypes are dependent on dominant and recessive alleles
• segregation: 2 alleles seperate from each other into gametes during meiosis 1
• independent assortment: when gametes are formed, genes segregated independently due to the independent assortment of non-homologous chromosomes

Question 18

Describe Mendel’s pea experiment

Answer 18

He crossed 2 pure breeding lines. White flower and purple flowered pea plants. The white flower was lost in F1 but reappeared in F2
- saw a 3:1 ratio
Concluded that one trait was dominant. (No co-dominance)

Question 19

What is hemizygous?

Answer 19

Only get one copy of a gene (e.g. males only get 1 X chromosome and one only copy of each of those genes) therefore, they will always express that allele

Question 20

Why are recessive alleles recessive?

Answer 20

Difference is at the nucleotide level. Usually the recessive allele has some sort of nucleotide mutation resulting in a non-functional protein (e.g. white flower, pigment)

Question 21

What is a SNP and how are they used?

Answer 21

SNP= single nucleotide polymorphism
A single base pair
They are used as markers on genes to Mark areas of interest

Question 22

How is the probability of 2 genes recombining affected by the distance between them?

Answer 22

Larger distance between them, greater chance of recombination

Question 23

What does it mean if two genes / loci are linked?

Answer 23

They are on the same chromosome

Question 24

What is 1 cM equivalent to?

Answer 24

1 in 100 times that meiosis happens, the two loci will be recombinant (separated)
E.g. 25 cM = 25% of the time they will be separated and will end up on different chromosomes

Question 25

What is a goal of recombination mapping?

Answer 25

To determine if the two genes are linked, and if they are, how far apart they are.

Question 26

What notation is used to indicate genes that are linked?

Answer 26

An underscore

Question 27

Why can you not tell recombination has occurred in homologous chromosomes?

Answer 27

Because they are identical

Question 28

What are the two different types of recombination in heterozygous parents?

Answer 28

Cis and trans.
Cis = dominant alleles on the same chromosome/tid
Trans = 1 dominant and 1 recessive on each

Question 29

How can you tell if a hetereozygote was in cis or trans?

Answer 29

By examining the progeny

The parental types are more common than recombinants

Question 30

How to work out cM?

Answer 30

Recombinant progeny / total