Separate Biology - B6 Inheritance, Variation and Evolution Flashcards
Which type of cell division leads to identical cells being formed?
Mitosis
Name the gametes (sex cells) in animal reproduction.
Sperm (male) and egg (female)
Which type of reproduction leads to a variety in the offspring as there is mixing of genetic information?
Sexual reproduction
What is a clone?
Genetically identical offspring (a result of asexual reproduction)
Which type of cell division leads to non-identical cells being formed?
Meiosis
Name the gametes (sex cells) in plant reproduction.
Pollen (male) and egg cells (female)
Which type of reproduction leads to genetically identical offspring?
A-sexual reproduction
Before meiosis, there are 46 chromosomes in a human body cell. How many are there in each gamete after meiosis?
23
Describe the structure of DNA
A polymer made up of two strands forming a double helix.
What is the name for a specific section of DNA that codes for a particular protein?
A gene
What is the genome of an organism?
The entire genetic material of that organism
Give three reasons why understanding the human genome is important.
- Genes linked to different types of disease can be searched for
- Inherited disorders can be understood / treated
- Migration patterns of the past can be traced
Before cell division, what does the DNA in the cell get stored in?
Chromosomes
What does a gene code for?
A particular sequence of amino acids, which make specific proteins
Complete the Punnett square for the % chance of having a mouse with black fur.
F = brown fur, f = black fur
0% chance of having a mouse with black fur
What is embryo screening?
Removing a cell from an embryo and analysing its DNA to look for genetic disorders
Explain what is meant by a ‘dominant allele’
The characteristic is expressed if one or two copies of the allele is present
What name is given to two of the same alleles (e.g TT or tt)?
homozygous
What does ‘genotype’ mean?
What alleles an organism has, e.g. Tt, TT or tt
What is an allele?
A version of a gene
Explain what is meant by a ‘recessive allele’
The characteristic is only expressed if two copies of the allele are present.
What name is given to two different alleles (e.g Tt)?
heterozygous
What does ‘phenotype’ mean?
The characteristics an organism has, e.g. ‘long hair’, ‘black fur’, ‘blue eyes’ e.t.c
Give an example of characteristics controlled by a single gene
Fur colour in mice / red-green colour blindness in humans
Is polydactyly caused by a dominant or recessive allele?
Dominant
Complete the Punnett square for the % chance of having a boy or girl
50% male, 50% female
What is cystic fibrosis?
A genetic disorder that affects cell membranes and causes mucus build up in the air passages and pancreas.
Is cystic fibrosis caused by a dominant or recessive allele?
Recessive
Are most characteristics determined by a single gene, or by multiple genes interacting?
Multiple genes interacting
What is polydactyly?
An inherited disorder that causes a person to have extra fingers or toes.
How many pairs of chromosomes are found in ordinary human body cells?
23 pairs
22 pairs of chromosomes determine an organism’s characteristics, but what does the 23rd pair determine?
The 23rd chromosome determines sex
(XX in female and XY in male)
What is variation?
Differences in the characteristics of individuals in a population
Which of the following is true?
a) Most mutations of DNA cause a change in phenotype
b) Most mutations of DNA do not cause a change in phenotype
b) Most mutations of DNA do not cause a change in phenotype
As well as genotype, what else affects the phenotype of an organism?
The environment
What causes genetic variation?
Mutations
What is evolution?
A change in the inherited characteristics of a population over time which may result in the formation of a new species
When are two organisms with a common ancestor considered to be two different species?
When they cannot interbreed and produce fertile offspring.
Describe how selective breeding works
- Choosing parents with a desired characteristic
- Breed them
- Select offspring with the desired characterstic
- Breed them
- Continue over many generations until you have a population with the desired characteristic.
Give two examples of “desired characteristics” in the selective breeding of animals
- Animals which produce more milk / meat
- Domestic dogs of a gentle nature
According to the theory of evolution by natural selection, what have all species of living things evolved from?
Simple life forms that first developed more than three billions years ago.
Describe how speciation occurs
- Isolation of two populations.
- Differences in environmental conditions or food availability in the two areas.
- Natural variation in populations.
- Mutations occur.
- Individuals that are better adapted to their environment…
- …survive, reproduce and produce offspring.
- Populations become so genetically different that they can’t interbreed and produce fertile offspring.
Give two examples of “desired characteristics” in the selective breeding of plants
- Disease resistance in food crops
- Large / unusual flowers
What are the negative consequences of selective breeding?
- Inbreeding causes a reduction in gene pool.
- Reduced variation in genes means the population is less resistant to disease
- Inbreeding can cause populations to have genetic defects.