Inheritance , Variation and Evolution

Question 1

what is the difference between meiosis and mitosis?

Answer 1

meiosis leads to non-identical cells
being formed while mitosis leads to identical cells being formed.

Question 2

what is sexual reproduction?

Answer 2

Sexual reproduction involves the joining (fusion) of male and female gametes:
* sperm and egg cells in animals
* pollen and egg cells in flowering plants.
In sexual reproduction there is mixing of genetic information which leads to variety in the offspring. The formation of gametes involves
meiosis

Question 3

what is asexual reproduction?

Answer 3

Asexual reproduction involves only one parent and no fusion of
gametes. There is no mixing of genetic information. This leads to
genetically identical offspring (clones). Only mitosis is involved.

Question 4

explain how meiosis halves the number of chromosomes in gametes and fertilization restores the full number of chromosomes?

Answer 4

Cells in reproductive organs divide by meiosis to form gametes.
When a cell divides to form gametes:
* copies of the genetic information are made
* the cell divides twice to form four gametes, each with a single
set of chromosomes
* all gametes are genetically different from each other.
Gametes join at fertilization to restore the normal number of chromosomes. The new cell divides by mitosis. The number of cells increases. As the embryo develops cells differentiate.

Question 5

describe the structure of DNA:

Answer 5

The genetic material in the nucleus of a cell is composed of a chemical called DNA. DNA is a polymer made up of two strands forming a double helix. The DNA is contained in structures called chromosomes.

Question 6

what is a gene?

Answer 6

A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.

Question 7

define the term genome:

Answer 7

The genome of an organism is the entire genetic material of that organism.

Question 8

discuss the importance of
understanding the human genome.

Answer 8

• search for genes linked to different types of disease
• understanding and treatment of inherited disorders
• use in tracing human migration patterns from the past.

Question 9

what is a gamete?

Answer 9

Gametes are an organism’s reproductive cells. They are also referred to as sex cells.

Question 10

what is a chromosome?

Answer 10

a long DNA molecule with part or all of the genetic material of an organism

Question 11

what is a gene?

Answer 11

A segment of DNA that codes for a particular characteristic or protein. (It is the unit of inheritance)

Question 12

what is an allele?

Answer 12

an allele is a variation of the same sequence of long DNA

Question 13

what is a homozygous allele?

Answer 13

When two alleles for a gene are the same version
Eg - both alleles are blue for eye colour, so the person is homozygous

Question 14

what is a heterozygous allele?

Answer 14

When two alleles for a gene are different versions
Eg - both one allele is blue for eye colour, and the other is brown - so the person is heterozygous

Question 15

what is a dominant allele?

Answer 15

When displayed the characteristic is always shown - only need one of them
Can be heterozygous or homozygous
E.g BB or Bb

Question 16

what is a recessive allele?

Answer 16

Only shown when the alleles are the same (homozygous)

E.g bb - blue eyes

Question 17

what is a genotype?

Answer 17

The allele pair for a characteristic. Eg - one Brown (B) & one blue (b) allele
genotype= Bb

Question 18

what is a phenotype?

Answer 18

The physical expression of the genotype (what the genotype causes)

Question 19

Name two inherited disease and explain how they passed on?

Answer 19

• Polydactyly (having extra fingers or toes) is caused by a
  dominant allele.
• Cystic fibrosis (a disorder of cell membranes) is caused by a
  recessive allele.

Question 20

Explain how sex is determined

Answer 20

Ordinary human body cells contain 23 pairs of chromosomes.
22 pairs control characteristics only, but one of the pairs carries the
genes that determine sex.
* In females the sex chromosomes are the same (XX).
* In males the chromosomes are different (XY).

Question 21

Differences in the characteristics of individuals could be due to:

Answer 21

• the genes they have inherited (genetic causes)
• the conditions in which they have developed (environmental
  causes)
• a combination of genes and the environment.

Question 22

how much variation is there between a species?

Answer 22

here is usually extensive genetic variation within a
population of a species

Question 23

How do variations arise?

Answer 23

variants arise from mutations and that: most
have no effect on the phenotype; some influence phenotype;
very few determine phenotype.

Question 24

Mutations occur continuously. Very rarely a mutation will lead to a new phenotype. what does this cause?

Answer 24

If the new phenotype is suited to an environmental
change it can lead to a relatively rapid change in the species.

Question 25

What does the theory of evolution by Natural selection state?

Answer 25

The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.

Question 26

What happens if two populations become so different?

Answer 26

If two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring they have formed two new species.

Question 27

What is selective breeding?

Answer 27

Selective breeding (artificial selection) is the process by which humans breed plants and animals for particular genetic characteristics. Humans have been doing this for thousands of years since they first bred food crops from wild plants and domesticated animals

Question 28

What does selective breeding involve?

Answer 28

Selective breeding involves choosing parents with the desired characteristic from a mixed population. They are bred together. From the offspring those with the desired characteristic are bred together. This continues over many generations until all the offspring show the desired characteristic

Question 29

What example characteristic are chosen?

Answer 29

* Disease resistance in food crops. * Animals which produce more meat or milk. * Domestic dogs with a gentle nature. * Large or unusual flowers

Question 30

What is a problem with selective breeding?

Answer 30

Selective breeding can lead to ‘inbreeding’ where some breeds are particularly prone to disease or inherited defects.

Question 31

What have plant crops be genetically engineered to do?

Answer 31

Plant crops have been genetically engineered to be resistant to diseases or to produce bigger better fruits.

Question 32

What have bacterial cells been genetically engineered to do?

Answer 32

Bacterial cells have been genetically engineered to produce useful substances such as human insulin to treat diabetes.

Question 33

What happens in genetic engineering involving genes?

Answer 33

In genetic engineering, genes from the chromosomes of humans and other organisms can be ‘cut out’ and transferred to cells of other organisms.

Question 34

What are GM crops?

Answer 34

Crops that have had their genes modified in this way are called genetically modified (GM) crops. GM crops include ones that are resistant to insect attack or to herbicides. GM crops generally show increased yields.

Question 35

What are concerns with GM crops

Answer 35

Concerns about GM crops include the effect on populations of wild flowers and insects. Some people feel the effects of eating GM crops on human health have not been fully explored

Question 36

Explain the process of genetic engineering?

Answer 36

* enzymes are used to isolate the required gene; this gene is inserted into a vector, usually a bacterial plasmid or a virus * the vector is used to insert the gene into the required cells * genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics.

Question 37

What evidence for Darwin's theory ?

Answer 37

Evidence for Darwin’s theory is now available as it has been shown that characteristics are passed on to offspring in genes. There is further evidence in the fossil record and the knowledge of how resistance to antibiotics evolves in bacteria.

Question 38

What are Fossils?

Answer 38

Fossils are the ‘remains’ of organisms from millions of years ago, which are found in rocks.

Question 39

How are Fossils may be formed?

Answer 39

* from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent * when parts of the organism are replaced by minerals as they decay * as preserved traces of organisms, such as footprints, burrows and rootlet traces.

Question 40

Why were there few traces of early forms of life?

Answer 40

Many early forms of life were soft-bodied, which means that they have left few traces behind. What traces there were have been mainly destroyed by geological activity. This is why scientists cannot be certain about how life began on Earth

Question 41

What can er learn from fossils?

Answer 41

We can learn from fossils how much or how little different organisms have changed as life developed on Earth.

Question 42

When does extinction occur?

Answer 42

Extinctions occur when there are no remaining individuals of a species still alive

Question 43

Why are Mutations of bacterial pathogens that produce new strains dangerous?

Answer 43

Mutations of bacterial pathogens produce new strains. Some strains might be resistant to antibiotics, and so are not killed. They survive and reproduce, so the population of the resistant strain rises. The resistant strain will then spread because people are not immune to it and there is no effective treatment.

Question 44

What is a bacteria that is resistant to antibiotics?

Answer 44

MRSA is resistant to antibiotics

Question 45

How is the rate of development of antibiotic resistant strains reduced?

Answer 45

* doctors should not prescribe antibiotics inappropriately, such as treating non-serious or viral infections * patients should complete their course of antibiotics so all bacteria are killed and none survive to mutate and form resistant strains * the agricultural use of antibiotics should be restricted.

Question 46

How are living things dived into groups?

Answer 46

Traditionally living things have been classified into groups depending on their structure and characteristics in a system developed by Carl Linnaeus.

Question 47

How did Carl Linnaeus divide things?

Answer 47

Linnaeus classified living things into kingdom, phylum, class, order, family, genus and species. Organisms are named by the binomial system of genus and species.

Question 48

What is the three domain system

Answer 48

Due to evidence available from chemical analysis there is now a ‘three-domain system’ developed by Carl Woese. In this system organisms are divided into: * Archaea (primitive bacteria usually living in extreme environments) * Bacteria (true bacteria) * Eukaryota (which includes protists, fungi, plants and animals).

Question 49

What are evolutionary trees used for?

Answer 49

Evolutionary trees are a method used by scientists to show how they believe organisms are related. They use current classification data for living organisms and fossil data for extinct organisms.