B1 Smart Teach Foundation Session 3

Keywords Key wordDefinition NucleusPlace inside a cell that contains the DNA (chromosomes). DNAA molecule found in the nucleus of cells, it’s job is to give instruction to make proteins. GeneA section of DNA that codes for one protein. AlleleDifferent version of a gene (example: blue eye allele and brown eye allele). ChromosomeX shaped structure made of DNA (found in the nucleus). Genetic DisorderA physical problem caused by a different allele. CarrierSomeone who carries the allele for a genetic disorder without having the disorder. Recessive alleleA recessive allele only shows if the individual has two copies of the recessive allele. Dominant alleleA dominant allele always shows, even if the individual only has one copy of the allele. GenotypeDescribes the genetic make-up of an organism (the combination of alleles). Phenotypedescribes the observable, physical characteristics that an organism has.

Genetic Disorders Two genetic disorders you need to know about: Cystic Fibrosis – Over production of mucus Sickle Cell Disease – Abnormally shaped red blood cells.

Exam Question The diagram shows the genetic inheritance of cystic fibrosis (CF) in a family. Cystic fibrosis is a genetic disorder caused by the CF recessive allele. 1.What is an allele? 2.Complete the punnet square to show how cystic fibrosis is inherited if both parents are carriers. 3.Give the percentage chance of a child being a carrier of CF when both parents are carriers of CF. 50%

Punnet Squares Make sure you put the mothers alleles in the side labelled mother and the fathers alleles in the side labelled father. Dominant allele first. A carrier will always have one dominant allele and one recessive allele. If it asks for percentage chance, you must write the percentage.

Percentage chance = Probability =

Symptoms of Cystic Fibrosis An overproduction of thick sticky mucus which can lead to: -Weight loss -Infertility -Breathing problems -Tiredness -Problems with digestion

Exam Questions 1.Describe how cystic fibrosis can cause problems with the absorption of food and oxygen in a person with this disorder (3 marks). 2.Explain why a person can be underweight due to cystic fibrosis (2 marks).

Answers 1. Describe how cystic fibrosis can cause problems with the absorption of food and oxygen in a person with this disorder.

Answers 2. Explain why a person can be underweight due to cystic fibrosis (2 marks).

Sickle Cell Disease Sickle Cell Disease can cause a change in the shape of a red blood cell.

Eye colour inheritance Eye colour often comes up on the exam. The diagram below shows the inheritance of eye colour in a family. The allele for brown eyes is (B) and the allele for blue eyes is (b). 1.What is the genotype of Jacob? 2.What is the phenotype of Jenny? 3.Is Baby J male or female?

Eye Colour Punnet Square BROWN eyes (B) – Dominant blue eyes (b) – recessive

Exam Question 1.Explain why two parents with the alleles BB and bb for eye colour are unlikely to produce offspring with blue eyes. You should draw a genetic diagram or Punnett square to help with your explanation. Unlikely but not impossible Easy marks!!