B12. (Comb) Types of reproduction and DNA Flashcards
What is a gamete?
A gamete is a sex cell produced in the sex organs by meiosis (e.g. sperm cell, egg cell are gametes).
How many chromosomes do human sex cells contain in their nucleus?
They contain half the number of chromosomes compared to a normal body cell i.e. 23 chromosomes
Describe the structure of DNA
Deoxyribonucleic acid (=DNA) is the molecule in the nucleus that carries our genetic code. DNA is a double stranded, double helix molecule.
What is a chromosome?
A chromosome is a length of DNA. Chromosomes are arranged into pairs in the nucleus.
A gene is….
Genes are small sections of chromosomes (DNA) that code for a particular sequence of amino acids to make a specific protein.
What is an allele?
An allele is a different/alternate form of a gene.
For example: Gene is eye colour, the alleles could be brown, blue, green, etc.
Homozygous alleles are…
alleles that are the same e.g. BB or tt
Heterozygous alleles are…
alleles that are the different e.g. Bb or Tt
When are dominant alleles expressed?
Dominant alleles are alleles that are always expressed if they are present - even if only one copy is present e.g. Bb, BB.
When are recessive alleles expressed?
Recessive alleles are only expressed if there are 2 recessive alleles present e.g. bb (therefore no dominant allele is present).
What is meant by the term ‘genotype’?
The genetic makeup (alleles) of an individual. e.g., BB, Tt, ss.
What is meant by the term ‘phenotype’?
This describes the physical and biological characteristics expressed in an individual as determined by their genotype. e.g. Brown eyes, Tall, curly hair.
List the 2 types of reproduction
- Sexual reproduction
- Asexual reproduction
How many parents are involved in sexual reproduction?
Two parents - a male and a female
Which type of reproduction requires gametes e.g. sperm cell, egg cell?
Sexual reproduction
Why does asexual reproduction not require gametes?
Because in asexual reproduction only ONE parent is involved. There is no fusion of gametes.
Describe the offspring in asexual reproduction
They are all genetically identical to each other and the parent. They are clones.
Compare mitosis and meiosis in terms of number of divisions.
In mitosis there is one division, in meiosis there are two divisions.
What are the products of meiosis?
Four genetically different sex cells.
Name an advantage of sexual reproduction.
1) Produces variation in the offspring.
2) If the environment changes variation gives a survival advantage.
3) Natural selection can be speeded up by humans in selective breeding to increase food production.
Name an advantage of asexual reproduction.
1) Only one parent needed
2) More time and energy efficient as do not need to find a mate.
3) Faster than sexual reproduction.
4) Many identical offspring can be produced when conditions are favourable.
What are the sex cells of a plant?
Male sex cell = pollen grain
Female sex cell = ovule
In which type of reproduction is there variation in the offspring?
Sexual reproduction - because there is fusion of gametes.
