B6 Inheritance

What is sexual reproduction?

A process which involves the fusion of male and female gametes

What cells are involved in sexual reproduction in animals and in plants? (2)

Sperm and egg cells in animals

Pollen and egg cells in flowering plants

What is asexual reproduction? (2)

A process which involves only one parent and no fusion of gametes meaning only mitosis is involved

It produces clones

What is meiosis? (2)

When cells divide twice to form 4 gametes which are genetically different

The daughter cells have half the number of chromosomes as body cells

What happens during meiosis? (3)

The cell makes copies of its genetic information

The cell divides twice to form 4 gametes, each with a single set of chromosomes

All the gametes are genetically different from each other

What are gametes? (2)

An organism's reproductive cells, which have half the usual genetic information

each cell carries only one copy of each chromosome

What are the female and male gametes called in animals? (2)

Female is ova / egg cell

Male is sperm cell

What is DNA? (2)

The chemical that a cell's genetic information is composed of

It is a polymer, made up of two strands forming a double helix

Where is DNA found?

Organised into chromosomes in the nucleus

What is a gene? (2)

A small section of DNA on a chromosome

Each makes a code for a unique chain of amino acids

What is a genome?

All of the genetic material of an organism

Why is it important that scientists now understand the human genome? (3)

It allows us to:

search for genes linked to different types of disease

understand and treat inherited disorders

trace human migration patterns from the past

What is an allele?

One of two or more versions of a gene

What are dominant and recessive alleles? (3)

The combination of a pair of alleles determines the trait expressed

A dominant allele is always expressed, even if only one copy is present (Bb or BB)

A recessive allele is only expressed if two copies are present (bb)

Define heterozygous and homozygous (2)

Homozygous: a gene that has two identical alleles (Bb or bb)

Heterozygous: a gene that has two different alleles (Bb)

Give two examples of disorders caused by variation in a single gene (2)

Polydactyly (having extra fingers or toes)

Cystic fibrosis (a disorder of cell membranes)

Is polydactyly caused by a recessive or dominant allele?

Dominant

Is cystic fibrosis caused by a recessive or dominant allele?

Recessive

How many pairs of chromosomes do ordinary human body cells contain?

23 pairs

How many chromosomes do human gametes have?

23 (23 only, NOT 23 pairs)

What are the sex chromosomes in males and females? (2)

Females: XX
Males: XY

What is a species?

A group of organisms with similar characteristics which can interbreed to produce fertile offspring

What is variation?

Differences in the characteristics of individuals in a population

What can cause variation within a population? (3)

The genes organisms inherit (genetic causes)

The conditions in which they develop (environmental causes)

A combination of genes and the environment

What are mutations?

Random alterations in DNA which occur continuously

What is evolution?

the inherited characteristics of populations over successive generations, which occurs through natural selection

What does the theory of evolution state?

all species of living things have evolved from simple life forms that first developed more than three billion years ago

Who proposed the theory of evolution by natural selection?

Charles Darwin

What is selective breeding?

when humans breed plants and animals for particular genetic characteristics

What has selective breeding been used to produce? (4)

Disease resistant food crops

Animals which produce more meat or milk

Domestic dogs with a gentle nature

Large or unusual flowers

What is the main drawback of selective breeding? (2)

Leads to inbreeding, where organisms are particularly prone to inherited defects and disease

a disease that can kill one can likely kill them all

What is genetic engineering?

when the genome of an organism is changed, by introducing a gene from another organism

What has genetic engineering been used to produce? (3)

plant crops that are disease resistant

plants that produce more flowers/fruit/veg

bacterial cells that produce useful substances eg. human insulin

What are fossils?

The remains of organisms from millions of years ago, embedded in rocks

Why is the fossil record incomplete?

Many early forms of life were soft-bodied, so few fossils formed, and they have been destroyed over time

What can be learned from fossils?

How much different organisms have changed as life developed on Earth

What is extinction?

when there are no remaining individuals of a species still alive

Why can bacteria evolve rapidly?

They reproduce at a high rate

How can a strain of bacteria become resistant to an antibiotic? (4)

Mutations of bacteria produce new strains

Some strains may be resistant to antibiotics, and so are not killed

These ones survive and reproduce

The resistant strain will then spread

Give an example of an antibiotic-resistant bacterium.

MRSA

What can and should be done to reduce the rate of development of antibiotic resistant strains? (3)

Doctors should not prescribe antibiotics inappropriately

Patients should complete their course of antibiotics

Antibiotics shouldn't be used too much on farms

Why is antibiotic resistance such a big problem?

The development of new antibiotics is expensive and slow

How did Linnaeus classify living things? (7)

Kingdom

Phylum

Class

Order

Family

Genus

Species

What are the three domains in the 'three-domain system' of classification of living organisms? (3)

Archaea → primitive bacteria, usually living in extreme environments

Bacteria → true bacteria

Eukaryota → includes protists, fungi, plants and animals

Who developed the 'three-domain system' of classification of living organisms?

Carl Woese

What is a phenotype? (2)

An organism's observable characteristics, both internal and external

They are determined by its genotype and the surrounding environment

What is a genotype?

the combination of alleles an organism has for a particular characteristic

What is mitosis?

The process where a cell replicates its chromosomes, splits them, then splits itself to produce two identical daughter cells

What happens in mitosis? (3)

The cell’s chromosomes are replicated meaning there are 46 pairs of chromosomes

The chromsomes split and move to the poles of the cell

The cell pinches then splits in half to form two genetically identical daughter cells