B1 You and Your Genes Q3 Question: What are alleles?

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1 Q1 : Where are chromosomes found within a cell? Inside the nucleus. Q2 : Put the following in size order starting with the smallest first: nucleus, chromosome, cell, gene. Gene, chromosome, nucleus, cell. Q3 : What are alleles? Alleles are different versions of the same gene. Q4 What are genes and how do they control the different characteristics we develop? A gene is a short section of DNA that codes for a protein. Proteins are the building blocks of cells. Having different versions of proteins means that we end up with different characteristics.

2 Q5 : What do the words genotype and phenotype mean? Genotype all of the genes that an organism has. Phenotype the characteristics that an organism displays. Q6 Is a person s weight determined by genes, the environment or a combination of both? A combination of both. Q7 What is the difference between a structural and a functional protein? Q8 : What is variation and what causes it? A structural protein is part of something e.g. collagen in skin. A functional protein has a job to do e.g. enzymes. Variation is the difference within and between species. Variation is due to genes and environmental factors.

3 Q9 Name the two types of sex cell. Sperm Egg Q10 How many chromosomes are found in sex cells? Why is this? Half the normal amount of DNA. In humans this means there are 23 chromosomes. They have half the amount so that when the sperm fertilises the egg there are 23 pairs. Q11 Why do most children look a bit like their parents but not identical to either. Half of their chromosomes have come from each parent. This means that they look similar because they get some of their alleles from each parent. They look different because they haven t got all the same alleles as either parent. Q12 What is the difference between homozygous and heterozygous? Homozygous both alleles are the same. Heterozygous the alleles are different.

4 Q13 Cystic fibrosis is caused by a recessive allele f. Use a diagram to show the chance of a child inheriting the disorder if both parents are carriers. F F FF Ff f Ff ff f Q14 If a disease is caused by a recessive allele, a person with one copy of the allele won t show any symptoms. What are they know as? Carriers. There is a 1 in 4 (25%) chance. Q15 What sex chromosomes do human males have? X and Y Q16 How does a gene on one of the human sex chromosomes cause embryos to develop into males? The Y chromosome carries a gene that makes a protein that causes the development of testes. The testes then produce male sex hormones.

5 Q17 Give an example of a recessive genetic disorder and a dominant genetic disorder. Recessive Cystic fibrosis Dominant Huntington s disease Q18 What are the symptoms of cystic fibrosis? Thick, sticky mucus in the air passages, gut and pancreas. Breathing difficulty. Chest infections. Problems digesting food (so may be short/thin). Q19 What are the symptoms of Huntington s disease? Tremors Clumsiness Memory loss Poor concentration Mood changes Q20 Use a genetic diagram to show the possibility of a child inheriting Huntington s disease if one of their parents has one copy of the faulty allele? Use H and h to represent the alleles. There is a 50% chance. H h h Hh hh h Hh hh

6 Q21 During IVF treatment, what is the process of testing embryos to see if they have a genetic disorder called? Pre-implantation genetic diagnosis (PGD). Q22 Other than testing embryos during IVF, give one other use of genetic testing. Children, adults and a foetus in the womb can be tested to see if they carry alleles for genetic disorders. Children and adults can be tested before certain drugs are prescribed. Q23 What is a clone? How are they produced naturally? A clone is a genetically identical copy of an organism. They can be produced by asexual reproduction in bacteria and some plants. In plants this might be via runners or bulbs. Some animals can reproduce asexually e.g. aphids. When the cells of an embryo split, identical twins are formed. Q24 How are identical twins formed? Early in development the embryo splits into two and two separate embryos begin to develop.

7 Q25 If identical twins are clones, how can there be differences between them? Any differences are the result of environmental factors. Q26 Describe the process of producing an artificial clone. The nucleus of an egg cell is removed. A nucleus from an adult donor cell is placed into the empty egg cell. The cell is stimulated to that it starts dividing. The embryo is genetically identical to the donor cell. Q27 What are stem cells? A stem cell is unspecialised. It can develop into different types of cell. Q28 What is the difference between an embryonic stem cell and an adult stem cell? An embryonic stem cell has the potential to develop into any kind of cell. An adult stem cell can specialise into many cell types but not all cell types.

8 Q29 Describe how stem cells could be used to treat disease. Adult stem cells can be used to replace faulty cells e.g. for some blood diseases. Embryonic stem cells could be used to treat heart disease, diabetes, people with spinal injuries but these treatments are still being researched. Q30 Why might employers be interested in the results of a genetic test? They might not want to give a job to someone who is likely to get ill. Alternatively, they would be able to make sure that an employee wasn t exposed to something that might be dangerous because f the genes they have. Q31 What are the risks of genetic testing to a pregnant woman? The tests aren t 100% safe. There is a risk of infection and a 0.5-1% risk of miscarriage. Q32 What issues are there with genetic testing? Misinterpretation of results. Risk of miscarriage (if on a fetus). Should other family members be tested? Is it right for someone at risk of passing on a genetic condition to have children? Should a pregnancy be terminated? Discrimination (by employers). Life insurance may be refused.