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…

Fertilisation

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

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

DNA Structure

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

Summary