B5 Genes, inheritance + selection

Question 1

What is the genome?

Answer 1

-The entire genetic material of an organism.
-May influence the phenotype when interacting with its environment.
-Arranged as chromosomes and stored in the nucleus.

Question 2

What is the phenotype?

Answer 2

The visual characteristics of an individual.

Question 3

What is a chromosome?

Answer 3

Long, coiled up strand of DNA.

Question 4

What is a gene?

Answer 4

A short section of DNA that codes for a protein and therefore controls / helps other genes control a characteristic.

Question 5

What is variation?

Answer 5

The differences between individuals of the same species caused by genetic and environmental factors.

Question 6

What are the 2 causes of variation?

Answer 6

-Inherited / genetic: offspring inherit characteristics from their parents.
-Environmental: characteristics are impacted by the individual’s surroundings.

Question 7

Why don’t most mutations influence the phenotype?

Answer 7

Most DNA is non coding therefore mutations rarely cause a change in proteins.

Question 8

What is a mutation?

Answer 8

-A random / spontaneous change in the base sequence / quantity of DNA which causes the alleles to change and therefore produces genetic variants.
-Can be harmful / neutral / beneficial.

Question 9

What causes mutations?

Answer 9

Mutagens.

Question 10

What are coding genes?

Answer 10

Genes in the coding region of DNA.

Question 11

What is regulatory DNA?

Answer 11

Genes in the non-coding region of DNA.

Question 12

How can mutations in coding regions of DNA alter the activity of the protein that the altered DNA is meant to code for?

Answer 12

Change the shape of the protein made and make the protein non-functional.

Question 13

How can mutations in non coding regions of DNA still affect how genes are expressed?

Answer 13

By stopping the transcription of mRNA during protein synthesis and therefore stopping the production of the protein altogether.

Question 14

What is a promoter?

Answer 14

An example of regulatory DNA which determines which gene will be expressed.

Question 15

What are the 3 types of mutation?

Answer 15

-Insertion: When a nucleotide is added to the DNA sequence.
-Deletion: When a nucleotide is removed from the DNA sequence.
-Change: When the order of nucleotides is changed.

Question 16

What is sexual reproduction?

Answer 16

A source of variation due to the offspring acquiring half of their genes from each parent.

Question 17

What is asexual reproduction?

Answer 17

A form of reproduction that only requires a single parent and produces genetically identical offspring.

Question 18

What are the advantages of sexual reproduction?

Answer 18

-Variation in offspring leads to adaptations in a species.
-Only some organisms in a population will contain the adaptations required to cope with an environmental pressure and these organisms can reproduce, allowing the population to continue.

Question 19

What are the disadvantages of sexual reproduction?

Answer 19

-Requires 2 parents.
-Slower reproduction.
-Requires energy so not energy efficient.

Question 20

What are the advantages of asexual reproduction?

Answer 20

-If the parent is well adapted to the area, the offspring will share an identical set of characteristics.
-Only one parent needed so don’t require partner / pollination.
-Faster reproduction so large numbers of offspring produced quickly.

Question 21

What are the disadvantages of asexual reproduction?

Answer 21

Adverse changes to the environment may destroy the species as all the organisms are identical and therefore all will be affected.

Question 22

What is meiosis?

Answer 22

A form of cell division that produces 4 haploid gametes that are genetically different, ensuring variation in a species.

Question 23

How do cells in the reproductive organs form gametes?

Answer 23

They divide by meiosis.

Question 24

What are gametes?

Answer 24

Sex cells which have half the number of chromosomes as they only have one copy of each chromosome.

Question 25

What is a haploid cell?

Answer 25

Has 1 set of 23 chromosomes.

Question 26

What is a diploid cell?

Answer 26

Has 2 sets of 23 chromosomes.

Question 27

What is the process of meiosis?

Answer 27

1. The cell makes copies of its chromosomes so it has double the amount of genetic information. 2. The cell divides into 2 diploid cells, each with half the amount of chromosomes. 3. Each cell divides into 2 again to produce 4 haploid cells altogether. 4. These haploid cells are called gametes and are all genetically different from each other.

Question 28

Why does meiosis result in 4 genetically different haploid cells?

Answer 28

The chromosomes are shuffled during the process, resulting in random chromosomes ending up in each of the 4 cells.

Question 29

What are alleles?

Answer 29

Different forms of the same gene.

Question 30

Why do humans have 2 alleles for each gene?

Answer 30

They inherit one allele from each parent.

Question 31

What is the difference between a dominant allele and a recessive allele?

Answer 31

-Only 1 out of 2 alleles needs to be dominant for the dominant allele to be expressed and present in the phenotype. -Both alleles need to be recessive for the recessive allele to be expressed and present in the phenotype.

Question 32

What is homozygous?

Answer 32

When both inherited alleles are the exact same.

Question 33

What is heterozygous?

Answer 33

When both inherited alleles are different.

Question 34

What is the genotype?

Answer 34

The combination of alleles an individual has.

Question 35

Why do alleles exist in pairs?

Answer 35

At the time of fertilisation, one is inherited from the sperm and one from the egg.

Question 36

What are punnet squares?

Answer 36

Used to work out the chances of a trait being passed on.

Question 37

How do chromosomes work?

Answer 37

-22 pairs of chromosomes control the characteristics and each of these pairs looks very similar. -23rd pair carries sex determining genes and the 2 chromosomes can look different. -1 sex chromosome goes into each gamete when cells undergo meiosis.

Question 38

What are the sex chromosomes for a female?

Answer 38

XX

Question 39

What are the sex chromosomes for a male?

Answer 39

XY

Question 40

What was the work of Gregor Mendel?

Answer 40

-He worked in the monastery gardens and observed the characteristics passed on to the next generations in plants. -He carried out breeding experiments on pea plants using different species and observed the offspring to see which characteristics they inherited.

Question 41

What were Gregor Mendel's conclusions?

Answer 41

-Offspring have some characteristics their parents have because they inherit hereditary units from each. -One unit is received from each parent. -Units can be dominant / recessive and can't be mixed together.

Question 42

When were chromosomes observed as part of cell division?

Answer 42

In the late 19th century.

Question 43

When was it discovered that chromosomes and units have similar behaviours and why?

Answer 43

In the 20th century and due to units being the genes on the chromosomes.

Question 44

When was the structure of DNA determined so that we could understand how genes worked?

Answer 44

1953