Transcript Who am I
Who am I? B1h OBJECTIVES Grade G-E • Analyse human characteristics to determine those caused by the environment, those controlled by genes and so inherited & those which are a result of both Grade D-C • State that gender (in mammals) is determined by sex chromosomes: XX (female) and XY (male) • Explain that genetic variation can be caused by: mutations (changes to the genetic code); gamete formation; fertilisation • Recall that inherited diseases are caused by faulty genes • State the causes of mutations Environmental differences Clearly, not all differences are due to just our genes… Variation due to inheritance only Variation due to environment only Variation due to a bit of both Boy or Girl? X Y X “Allele” Girl XX XY Boy Mother Boy or Girl? Son Father Daughter Eye colour In eye colour the brown eye allele is dominant, so we call it B, and the blue eye is recessive, so we call it b: BB Bb bb Homozygous brown-eyed parent Heterozygous brown-eyed parent Blue-eyed parent What would the offspring have? Eye colour Example 1: A homozygous brown-eyed parent and a blue-eyed parent: X BB Parents: Gametes: Example 2: 2 heterozygous brown-eyed parents bb Bb X Bb B B b b B b B b Bb Bb Bb Bb BB Bb bB bb (FOIL) Offspring: All offspring have brown eyes 25% chance of blue eyes Eye colour Example 3: A heterozygous brown-eyed father and a blue-eyed mother: Bb bb B b b b Bb Bb bb bb Equal (50%) chance of being either brown eyed or blue eyed. Another method Example 3: A heterozygous brown-eyed father and a blue-eyed mother: Father B b b Bb bb b Bb bb Mother Inherited diseases 1) Cystic fibrosis – a disease that causes thick and sticky mucus to coat the lungs, gut and pancreas. It’s caused by recessive alleles: Ff X Ff 2) Huntingdon's disease – a disease of the nervous system that causes shaking and eventually dementia. It’s caused by a dominant allele: Cc X cc 3) Sickle cell anaemia – a disease that alters the shape of red blood cells, thereby reducing their oxygen capacity, causing weakness and anaemia. It’s caused by recessive alleles: Ss X Ss Haemophilia in the royal family Worksheet B1h2