Lesson Starter How many chromosomes does almost all human cells have? How many chromosomes does human sex cells have? What does the word allele mean? Give an example of variation in humans Give an example of variation in plants

Inheritance Lesson 2

Learning Intention- lesson 2 To learn about environmental variation

Environmental Variation Characteristics can be affected by factors other than just genetics Think of examples of environmental differences between people

Environmental variation: copy Characteristics can be affected by factors other than just genetics Variation caused by surroundings is called ENVIRONMENTAL VARIATION Examples include: - Language spoken - Religion - Hair length - Weight - Piercings - Tattoos

Genetic Inheritance Sex cells (gametes) contain only one set of chromosomes. After fertilisation takes place the new cell (zygote) contains two sets of chromosomes. One set is from the father and the other set from the mother.

Genetic Inheritance Each parent contributes one piece of information to it’s offspring for each characteristic THEREFORE every inherited characteristic is controlled by two pieces of information The pieces of information can be the same or different

Genetic Inheritance Pieces of information are called genes (stored in chromosomes) Different versions of gene called alleles You inherit one allele from your Mum and one from your Dad for each gene- your genotype

Task: write down 3 characteristics that are inherited from the parents and 3 that are environmental

Task: write down 3 characteristics that are inherited from the parents and 3 that are environmental

Task: write down 3 characteristics that are inherited from the parents and 3 that are environmental

Task: write down 3 characteristics that are inherited from the parents and 3 that are environmental

Video What does the DOMINANT gene do to the RECESSIVE gene? What is the chromosome type of a girl and of a boy? What is haemophilia? What is the difference between normal RBC and RBC affected by thalassaemia? Where is there a successful screening programme for thalassaemia?

Genetic inheritance We receive two copies of the same gene (allele) Some genes are stronger than others. These genes are dominant. The weaker genes are recessive. Dominant genes can hide (mask) other genes that are not so strong.

Genetic Inheritance If an individual inherits a dominant gene for brown eyes from one parent and a recessive gene for blue eyes from the other, that person will have brown eyes. However, they would still carry a recessive gene for blue eyes which can be passed on to their offspring.

Genetic Inheritance: copy We receive two copies of the same gene (allele) however some genes are stronger than others. The stronger genes are called dominant and the weaker genes are recessive. Dominant genes can mask the recessive genes Eg: If you inherit a dominant gene for brown eyes from mum and a recessive gene for blue eyes from dad then you will have brown eyes. However, you would still carry a recessive gene for blue eyes which can be passed on to their offspring.

Genetic Crosses Dominant genes always appear in the physical characteristics (phenotype) of an organism- you only need one of them to have the characteristic. ​ However, a recessive gene is always hidden by a dominant one, and if you are to have that characteristic, you need to get two copies of the gene.​

Genetic Crosses: copy When carrying out genetic crosses, each gene is represented by using a letter. The letter used is a capital if the characteristic is dominant and lower case if the characteristic is recessive.

Phenotype Blue eyes x Brown eyes Genotype bb BB Gametes passed: Parents Phenotype Blue eyes x Brown eyes (recessive genes) x (dominant genes) Genotype bb BB Gametes passed: All b All B Offspring Genotype: all Bb Phenotype: all Brown eyes B B b Bb Bb b Bb Bb

Examples Dad has brown hair (Bb) and mum has blonde hair (bb) - What is the GENOTYPE of the offspring and what is the PHENOTYPE?