Topic 13 Triple Reproduction, DNA and Genetics Flashcards
Sexual reproduction involves the joining (fusion) of male and female gametes:
- sperm and egg cells in animals
- pollen and egg cells in flowering plants
Asexual reproduction involves only one parent and no fusion of gametes so:
There is no mixing of genetic information. This leads to genetically identical offspring (clones). Only mitosis is involved
In sexual reproduction there is mixing of
which leads to
The formation of gametes involves
genetic information
variety in the offspring
meiosis
Meiosis
fertilisation
halves the number of chromosomes
restores the full number of chromosomes
Cells in reproductive organs divide by meiosis to form gametes.
When a cell divides to form gametes:
copies of the genetic information are made
* the cell divides twice to form four gametes, each with a single set of chromosomes
* all gametes are genetically different from each other
Gametes join at
The new cell divides by
. The number of cells
As the embryo develops cells
fertilisation to restore the normal number of chromosomes.
mitosis.
increases
differentiate
Advantages of sexual reproduction:
produces variation in the offspring
* if the environment changes variation gives a survival advantage by natural selection
* natural selection can be speeded up by humans in selective breeding to increase food production
Advantages of asexual reproduction
- only one parent needed
- more time and energy efficient as do not need to find a mate
- faster than sexual reproduction
- many identical offspring can be produced when conditions are favourable
Some organisms reproduce by both methods depending on the circumstances. e.g
- Malarial parasites reproduce asexually in the human host, but sexually in the mosquito.
- Many fungi reproduce asexually by spores but also reproduce sexually to give variation.
*Many plants produce seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils.
that the genetic material in the nucleus of a cell is composed of
a chemical called DNA.
DNA
a polymer of two strands forming a double helix, contained in structures called chromosomes.
a gene
as a small section of DNA on a chromosome, coding for a particular sequence of amino acids, to make a specific protein.
Define a genome as the
entire genetic material of an organism.
Describe basic structure of a nucleotide:
consists of a common sugar, a phosphate group and one DNA base (A, C, G or T)
The DNA polymer is made up of
repeating nucleotide units.
In the complementary strands a C is always
on the opposite strand,
and a T
linked to a G
to an A.
mutations may occur
Most do not
or alter it only slightly so that
spontaneously
alter the protein
its appearance or function is not changed.
Ordinary human body cells contain
23 pairs of chromosomes.
Gamete
a reproductive cell of an animal or plant
Chromosome
A structure found inside the nucleus of a cell. A chromosome is made up of proteins and DNA organized into genes
Gene
a small section of DNA on a chromosome, that code for a particular sequence of amino acids, to make a specific protein.
Allele
each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.
Dominant allele
A dominant. allele is always expressed, even if one copy is present. Dominant alleles are represented by a capital letter, for example, A
recessive allele
A recessive allele is only expressed if the individual has two copies and does not have the dominant allele of that gene.
Homozygous
alleles are both identical for the same characteristic, for example AA or aa.
Heterozygous
A homozygote is an individual who has identical alleles for a particular gene. Heterozygous. alleles are both different for the same characteristic, for example Aa.
Genotype
the combination of alleles an organism has
Phenotype
The observable characteristics of an organism (seen just by looking - like eye colour, or found – like blood type)
some disorders are caused by inheritance of certain alleles:
Cystic fibrosis (a disorder of cell membranes) is caused by a recessive allele
Polydactyly (extra fingers or toes) is caused by a dominant allele
