Reproduction Flashcards
Explain the term heredity
The process of transmitting genetic information from one generation to the next
Describe the key features of the two different types of reproduction?
- Sexual reproduction - two parent organisms - produce genetically different offspring - fusion of male and female gametes - gametes produced by meiosis- half the number of chromosomes from the parents - mixing of genetic material produces variation
- Asexual reproduction - only one parent organism - produces genectically identical offspring (clones) - cell division is by mitosis - identical chromosomes as parent - no genetic variation
Explain binary fission
it is a type of asexual reproduction used by prokaryotic bacteria. The parent bacterium is replaced by two daughter bacteria when it divides into two.
Explain vegetative reproduction
Occurring in plants it is a form of asexual reproduction by producing runners, tubers or bulbs. The offspring are clones of the parent.
Explain the difference between self pollination and cross pollination in plants
Pollination is a form of sexual reproduction in plants whereby the pollen cell (male gamete) meets the egg cell (female gamete). It forms a zygote which becomes and embryo and then a seed.
If the pollen is transferred from a different plant it is cross pollination.
If the pollen is from the same plant it is self pollination
Explain the difference between identical and non identical (fraternal) twins
Identical twins are formed when a single ovum (egg) is fertilised, as the cells divide it splits into two. Each then continues to divide and embed in the uterus. The twins are genetically identical and any differences are caused by environmental differences such as diet, scarring haircuts etc
Non identical twins are formed when two ova are released at the same tim which are then fertilised by two different sperm. They are genetically different and can be different genders.
Describe mitosis and the type of cells it produces
Mitosis is a form of cell division.
The chromosomes of the cell duplicate by splitting longitudinally.
They then line up opposite their partner across the centre of the cell.
The chromosomes are then pulled to opposite ends of the cell.
The cell then divides into two, with each new cell having the full set of chromosomes.
These cells are therefore diploid.
Mitosis replicates cells for growth and repair as well as asexual reproduction.
Describe meiosis and the type of cells it produces
The first stage of meiosis is the same as mitosis the chromosomes duplicate, line up across the middle of the cell and migrate to opposite ends. Two daughter cells are produced. However there is a 2nd stage, the chromosomes and their copies line up in the middle of the daughter cells, the split from their copies and migrate again. the cell membranes pinch in forming 4 haploid cells.
Each haploid has half the number of chromosomes and they are genetically different. This is because it is random as to which of a pair of chromosomes ends up in which half of the gamete.
Explain the term gamete
Gametes are sex cells.
They contain half the number of chromosomes than a parent cell, in humans 23 instead of 46.
Gametes fuse together during sexual reproduction giving the offspring half of it’s chromosomes from each parent.
In this way organisms formed by sexual reproduction demonstrate variation.
in humans the possible combinations are 2 to the power 23
Describe how a genome carries our genetic information
A genome is one copy of all of the DNA found in an organisms diploid cells, it is it’s entire genetic material.
In humans the genome consists of about 20,000 genes.
A gene is a short section of DNA contained in a chromosome.
Human nuclei contain 23 pairs of chromosomes, one of each pair is inherited from each parent.
The DNA is tightly coiled in each chromosome, human DNA if uncoiled would be about 2 m long.
Where is DNA found and what is it’s role.
DNA is a polymer consisting of two strands shaped as a double helix.
It is present in the chromosomes which are in the nuclei of almost every cell in the body.
DNA provides your body with information on how to make proteins, including hormones and enzymes. They contain all of the genetic information about the organism including details such as eye colour and blood group. Unless you are an identical twin your genetic code carried in your DNA is unique to you.
What is the human genome project?
You could be asked an evaluation question about this so identify some advantages and disadvantages of it.
The HGP is the largest collaborative science project ever undertaken. 20 universities across the world worked together to identify the sequence of the 20 billion base pairs which make up human genes.
Advantages
Can identify and therefore prevent genetic diseases such as cystic fibrosis and breast cancer
Allows us to trace human migration patterns amongst different ethnic groups
Disadvantages
Could be used to discriminate against people who may be more likely fall ill, either by employers or heath insurance companies
What in an allele?
We have 2 pairs of chromosomes and therefore 2 pairs of each gene, one inherited from each parent.
The two versions of each gene are called alleles, you have alleles for all kinds of information such as eye colour or blood group.
Some alleles are dominant and others are recessive, therefore we may display a characteristic (dominant) but still carry the information for the other (recessive), which can then be passed on to the next generation.
Explain the difference between a genotype and a phenotype
Both describe how a gene will give certain characteristics such as eye colour.
The genotype is the information represented by letters such as BB, Bb or bb in the case of eye colour.
A phenotype is the characteristic explained in words eg blue eyes or brown eyes.
Explain the difference between homozygous and heterozygous genotypes.
Homozygous genotypes contain two identical alleles which can be either dominant or recessive. Eg BB or bb
Heterozygous genotypes contain two different alleles one dominant and one recessive. Eg Bb
