Reproduction Flashcards
What is a chromosome?
A large molecule of DNA
What is a gene?
A small section of DNA that codes for a particular sequence of amino acids that make a specific protein
What is the genome of an organism?
The entire genetic material of an organism (including all of the chromosomes and the mitochondria).
How many chromosomes do humans have?
46 (23 pairs) in most cells. Gametes have half of this number (23).
Describe the structure of DNA.
DNA is a polymer made up of two strands, which form a double helix.
How many bases code for a particular amino acid?
3
Describe the importance of the order of bases in DNA.
The order of bases controls the order in which amino acids are assembled into a protein.
What is involved in sexual reproduction?
The joining of male and female gametes, which results in a mixing of genetic information.
What is involved in asexual reproduction?
1 parent (no gametes). There is no mixing of genetic information, leading to genetically identical offspring (clones).
What are gametes?
Sex cells (eggs and sperm cells) which have half the number of chromosomes as an ordinary cell.
Why do body cells divide?
- Replace worn-out cells
- Repair damaged tissues
- For growth of the organism
Which process allows division of body cells?
Mitosis
What must happen before mitosis can occur?
The DNA doubles (DNA replication)
Outline the 3 main stages of mitosis.
1 - DNA replicates to produce 2 copies of each chromosome and sub-cellular structures increase in number;
2 - one set of chromosomes is pulled to each end of the dividing cell and the nucleus divides;
3 - the cytoplasm and the cell membrane also divide to form 2 identical daughter cells
Compare the cells that are produced (daughter cells) by mitosis to the parent cell.
They are genetically identical as the DNA is copied
Which cells undergo meiosis and what do they form?
Cells in the reproductive organs divide by osmosis to form the gametes (egg cells and sperm cells)
What happens when a cell divides by meiosis to form gametes?
The genetic material is copied and then the cell divides twice to form 4 genetically different cells, each with one set of chromosomes
Why do gametes have just 23 chromosomes instead of 46?
Two gametes join at fertilization to restore the number of chromosomes to 46.
How is mitosis different to meiosis?
In mitosis, cells divide once to produce two genetically identical daughter cells. The cells produced in mitosis each have 2 sets of chromosomes. In meiosis, cells divide twice to produce 4 genetically different daughter cells. The cells produced in meiosis each have one set of chromosomes.
What is an allele?
A different form of a gene (the combination of alleles inherited determines characteristics).
What are dominant alleles?
A form of the gene that controls the characteristic even if it is only present on 1 chromosome
What are recessive alleles?
A form of the gene that only controls the characteristic if it is present on both chromosomes
What is a homozygote?
An individual with two identical alleles for a characteristic e.g. BB or bb
What is a heterozygote?
An individual with different alleles for a characteristic e.g. Bb
What is a genotype?
This describes the alleles that are present for a particular characteristic e.g. Bb
What is a phenotype?
This describes the physical appearance of an individual for a particular characteristic e.g. brown fur
What is polydactyly?
More digits (fingers or toes) than normal
How is polydactyly inherited?
The allele is dominant. If a parent has polydactyly there is a 50% that offspring will have polydactyly.
What is cystic fibrosis?
A disorder of the cell membranes of cells lining the airways and pancreas. They have thick mucus so they get frequent lung infections and cannot digest food properly.
How is cystic fibrosis inherited?
The allele is recessive. If both parents are carriers there is a 25% chance that the offspring will have CF.
How can embryos or foetuses be screened for genetic disorders?
Cells have to be collected from the developing embryo/foetus.
Give some reasons why some people may be concerned about embryo screening.
- Risk of miscarriage
- false positive or false negative results
- could result in termination
- expensive.
How is sex determined in humans?
By the sex chromosomes (22 pairs of chromosomes control general body characteristics but one pair of chromosomes control the sex).
What are the female and male sex chromosomes?
Female - XX (homozygous); Male (XY - heterozygous)
What is variation?
The differences in characteristics of individuals in a population (e.g. hair colour in humans)
What causes variation?
Genetic causes, environmental cause or a combination of both genes and the environment.
What causes variation in genes?
Mutations - a change in the DNA code (many mutations have no effect, some influence phenotype and very few will determine phenotype).
What is a Zygote
A fertilised egg cell
