Noadswood Science, 2011
Inheritance & Genes
To understand how we inherit characteristics from our parents and how genes accomplish this
Wednesday, April 19, 2023
Inherited
Children usually look a little like their father, and a little like their mother, but they will not be identical to either of their parents
Why is this?
Offspring get half of their inherited features from each parent
During fertilisation, the nucleus from the sperm cell joins with the nucleus in the egg cell, and a new nucleus is formed with all the genetic information needed
Label a sperm and egg in as much detail as you can…
Fertilisation
Sperm cell (male) Egg cell (female)
Nucleus
Cytoplasm - contains a food (energy) store
Jelly coat - helps make sure only one
sperm can enter
NucleusHead - contains chemicals to help the cell get inside
the egg
Tail for swimming (note there is little cytoplasm, making the sperm cell
streamlined for swimming)
The sperm cell is extremely streamlined, with a powerful tail for swimming. It also has special chemicals in its head to help it penetrate the egg cell.
The egg cell is full of cytoplasm, used as an energy store for when fertilisation occurs. It also has a special barrier, which only allows one sperm to penetrate and fertilise it.
Both contain a nucleus, containing genes…
Genetic Information
The genetic information passed from parent to offspring is contained in genes, carried by chromosomes in the nucleus
All body cells have a nucleus which contains all genetic information
nucleus
Genetic Information
In a fertilised egg there are 23 pairs of chromosomes (23 unpaired chromosomes from your mother and 23 unpaired chromosomes from your father)
Chromosomes & Genes
A gene is a section of DNA that carries the code for a particular protein
Different genes control the development of different characteristics of an organism – many genes are needed to carry all the genetic information for a whole organism
Chromosomes, found in the cell nucleus, contain many genes
Species
The number of chromosomes and genes varies from species to species
For example, cells in human beings have 46 chromosomes (23 pairs) that carry about 30,000 genes in each cell; and cells in fruit flies have eight chromosomes that carry about 13,600 genes
DNA
Genes are made up of short lengths of DNA (deoxyribose nucleic acid)
In the 1950’s Watson and Crick were the first to come up with the structure of DNA
Alleles
Some characteristics are controlled by only one gene
Some genes have different forms, known as alleles
On each chromosome of the pair there can be different version of the same gene, i.e. blue or brown eyes – the variations are known as alleles
The allele expressed is the dominant gene
The allele not expressed is the recessive gene
DNA
Chromosomes and their genes are made of a molecule called DNA
DNA molecules carry the code that controls what your cells are made of and what they do
Each chromosome is a very long
molecule of tightly coiled DNA
DNA Investigation
Complete the DNA extraction experiment: -
1. Dissolve 3g of salt into 100cm3 of water in a 250cm3 beaker. Add 10cm3 of washing up liquid, and stir gently until it dissolves
2. Mash your fruit pieces using the pestle and mortar – when it is as mashed as possible put it into another 250cm3 beaker and add an equal volume of the solution made in the previous step to it – stir the mixture
3. Place the beaker inside a larger beaker of hot water, and leave for 15 minutes
4. Pour the mixture through a filter funnel with filter paper inside – collect the juice in a small beaker. Tilting the beaker slightly pour ice-cold ethanol down the side very slowly – stop when you have added as much ethanol as you have juice
Inherited
Some variations are inherited, whilst other variations are due to environmental factors
Inherited variation is a characteristic you have got from your parents - what can you inherit?
Gender Eye colour Hair colour Skin colour Lobed or lobeless ears
Lobed (left) & lobeless (right) ears