Topic 3 - Genetics

Question 1

Why is sexual reproduction a good/bad thing?

Answer 1

Good - genetic variation, different characteristics, more survive, leads to natural selection and evolution
Bad - Two parents needed and birth takes long time

Question 2

What is produced by meiosis?

Answer 2

Gametes - contain half number of chromosomes (opposite of diploid) eg egg or sperm cell

Question 3

What happens in meiosis?

Answer 3

Division one - Cell duplicates DNA
- Chromosomes line up in pairs in centre
- Pairs pulled apart with some of father’s and/or mother’s chromosomes
- Each cell is a mixture (genetic variation)
Division two - Chromosomes line up again and arms pulled apart
- Four haploid daughter cells, these are gametes with single set of chromosomes

Question 4

Why are haploid gametes needed for sexual reproduction?

Answer 4

Because they contain half the number of chromosomes needed to make a full set (zygote)

Question 5

What is an organisms genome?

Answer 5

All of an organisms DNA

Question 6

Where are genes found?

Answer 6

In section of DNA on a chromosome

Question 7

What is the function of genes?

Answer 7

To code for particular protein

Question 8

Where is DNA found in a cell and what are the bases?

Answer 8

Inside the nucleus, A, T, C, G

A pairs with T and G with C

Question 9

How are DNA strands held together? And structure

Answer 9

In a double helix with weak hydrogen bonds

Question 10

Describe an experiment to extract DNA from fruit cells

Answer 10

1) Mash strawberries and then put in beaker with detergent and salt. Mix well.
2) Salt makes DNA stick together
3) Filter mixture to get insoluble bits out
4) Add ice cold alcohol
5) DNA comes out of solution as it’s not soluble in alcohol so can be picked up with rod as white string.

Question 11

Where are all proteins made?

Answer 11

In the ribosomes in a cell’s cytoplasm

Question 12

How is the shape of a protein determined?

Answer 12

By reading the code in DNA so each protein has a different function. Each amino acid in a protein is coded by a sequence of three bases (base triplets)

Question 13

What happens in transcription of protein synthesis?

Answer 13

(Messenger RNA is a shorter single strand of nucleotides (polymer) (which use uracit (U) instead of thymine (T) as a base)). RNA polymerase is an enzyme involved in joining RNA to make MRNA.

1) RNA polymerase binds to region of non coding DNA in front of gene
2) DNA strands unzip and RNA polymerase moves along strand of DNA
3) Uses coding DNA to move mRNA and due to base pairss is complementary to the gene. Then mRNA moves out to join Riposome (from nucleus)

Question 14

What happens in Translation of protein synthesis?

Answer 14

1) Amino acids brought to Ribosomes by transfer RNA
2) Order of amino acids matches base triplets in mRNA called codens. These go to ribosomes.
3) The tRNA has an anticoden which makes sure amino acids bought to ribosome in correct order
4) Amino acids joined by ribosome to make a polypeptide (protein).

Question 15

What is a mutation?

Answer 15

A random change in DNA base sequence causing new alleles to arise

Question 16

How can mutations occur?

Answer 16

• In non-coding DNA as there are more genetic varients

- Can be inherited

Question 17

Effects of mutations on amino acid sequences

Answer 17

• It produces a genetic varient which can code for a different sequence of amino acids (changing shape and final protein and its function)

Question 18

How is transcription regulated?

Answer 18

By the production of mRNA

Question 19

Who discovered the base of genetics?

Answer 19

Gregor Mendel

Question 20

How did breeding pea plants work out the base of genetics?

Answer 20

• Helps us understand that characteristics are determined by hereditory units
• These units are passed on to offspring unchanged with one unit from each parent
• Hereditory units can be dominant or recessive
• Hereditory units are now called genes
• Dominant alleles are expressed.

Question 21

Why was it difficult to understand inheritance before idea of genes?

Answer 21

Because we had no understanding of cells and DNA

Question 22

Explain difference between genes and alleles

Answer 22

An allele is a variation of a gene

Question 23

What are the effects of alleles on inherited characteristics?

Answer 23

They change the phenotype of the organism and dictate the characteristics.

Question 24

What is the relationship between a phenotype and a genotype?

Answer 24

A genotype of the parent’s dictates the phenotype (characteristics) of offspring

Question 25

What is the difference between homozygous and heterozgous genotypes?

Answer 25

Heterozygous has two alleles that are different with one dominant and one recessive allele. Homozygous are two alleles which are the same. This can be either dominant or recessive.

Question 26

Why aren’t the effects of some alleles in an organisms genotype not seen in it’s phenotype?

Answer 26

Because they are recessive alleles

Question 27

How is sex determined in humans?

Answer 27

23rd pair of chromosomes is either XX or XY (male) when using genetic diagrams the chances of being male or female are 50% each.

Question 28

How are ABO blood groups an example of multiple alleles for one gene?

Answer 28

Blood types exist as four possible phenotypes: A, B, AB and O meaning you can have multiple allele inheritance which is displayed in blood types

Question 29

How are ABO blood types inherited?

Answer 29

Sometimes you have to have multiple alleles for a single gene. We inherit these alleles from our parents. 1O is recessive and 1A and 1B are dominant, however when they are together, you get AB blood type (which can be displayed in punnet squares. AB is called co-dominance

Question 30

Give an example of sex-linked genetic disorders

Answer 30

Haemophilia - blood doesn’t clot properly

Colour blindness too. People can be carriers of a disorder but it doesn’t show up but can on their offspring

Question 31

Why are some genetic disorders sex-linked?

Answer 31

Some diseases are carried on the X chromosome meaning if a boy has it on his X chromosome, he will have the disorder as they only have one whereas girls are XX so it’s less likely to show up so for example, boys are more likely to be colour blind

Question 32

Give examples of characteristics controlled by multiple genes

Answer 32

Blood groups

Question 33

Define ‘Mutation’

Answer 33

Changes in the base sequence of DNA

Question 34

How can we map the human genome?

Answer 34

The human genome project managed to map over 20,000 human genes to find every single gene. It helps us predict genes related to diseases so benefits for potential medicines.

Question 35

How can a mutation cause variation?

Answer 35

When a mutation occurs, it changes the base sequence of DNA forming new alleles (a different version of the same gene) which leads to genetic variation. This might mean the organism codes for a different protein, so it can’t carry out it’s function

Question 36

Give examples mutations that effect the phenotype and those that don’t

Answer 36

• Large effect: cystic fibrosis - mucus in lungs as body can’t digest properly making it hard to breath
• Small: hair colour, length
• None: some have no effect as they are neutral

Question 37

What is the difference between genetic and environmental variation?

Answer 37

Genetic variation is caused by organism having different alleles which lead to different phenotypes. Environmental variation is where an organism changes their phenotype to an environment’s acquired characteristics and they get throughout their lifetime

Question 38

What is the difference between continuous and discontinuous variation?

Answer 38

• Discontinuous variation = individuals fall into distinct classes or categories based on phenotypes eg blood type
• Continuous variation = complete range of measurements form one extreme to another eg height or shoe size

Question 39

What are the causes of genetic variation?

Answer 39

• Sexual reproduction leads to variation as there are two parents with different phenotypes
• Mutations also lead to genetic variation (base sequence)

Question 40

Describe causes of environmental variation

Answer 40

The conditions an organism is placed in can effect its phenotype, for example, if a green plant is placed in a dark room, over time it would grow spindly and yellow. However, height of an organism can be both environmental and genetic. This is the contribution of both genes and environment.