Flashcards
Variation and Inheritance
Cards in this deck (27)
- 1What is inside the nuclei of living cells?The nuclei contains chromosomes, which are made up of a string of genes, A chromosome is a single piece of coiled DNA containing many genes. Different genes control the development of different characteristics by issuing instructions to cells.
- 2What are chromosomes?They are long lengths of DNA (deoxyribonucleic acid).
- 3What does a DNA molecule consist of, and what information does it give?It consists of two strands which are coiled to form a double helix.
The DNA molecules in a cell form a complete set of instructions on how the organism should be constructed ad how its individual cells should work - 4What form are the instructions of DNA in?They are in a form of a chemical code made up of four bases, which hold the two strands of the molecule together.
- 5What does the order (or sequence) of the bases in DNA provide?The or.er (or sequence) of the bases in a particular region of DNA (a gene) provides the genetic code that controls cell activity and the development of the related characteristic.
- 6How many chromosomes does a human have?Most body cells have the same number of chromosomes, in matching pairs - humans have 23 pairs (46 chromosomes in total). Other species have different numbers of chromosomes, e.g. a chicken has 78 chromosomes.
- 7What do the gametes contain?The gametes (sex cells) contain individual chromosomes and therefore have exactly half the number of normal cells - 23 chromosomes in humans.
- 8What happens during gamete reproduction and how does this make variation in a species?During gamete production, chromosome combinations in each cell are mixed up so that no two gametes are the exactly the same. This is a source of variation. During sexual reproduction, when the male (sperm) and female (egg) gametes fuse, they produce a cell with the correct number of chromosomes. This process increases the amount of variation in a species because genetic information from two parents is mixed together to produce a unique individual.
- 9Why does asexual reproduction create clones?Because all the genes come from one parent. The offspring, which are genetically identical to the parent and to each other, are called clones.
- 10What might variation occur from?It may be due to genetic or environmental causes.
- 11How does genetic variation occur and what can it be caused by?It occurs because individuals inherit different combinations of genes. Genetic variation between individuals can be caused by:
Mutations which alter the genes.
Differences between individual gametes.
Random fusion of an egg with one out of millions of sperm at fertilisation. - 12Where do the genes which code for characteristics occur?They occur in pairs called alleles. These are alternative forms of a gene.
- 13Give some examples of environmental variation?It happens because individuals develop in different conditions - for example, spoken language and scars.
- 14Often variation is due to a combination of genetic and environmental causes, give some examples of this.In characteristics like:
Height
Body mass
intelligence - 15Which chromosome combination makes a female and which makes a male?XX = female
XY = male - 16What do they egg and sperm cells carry, and hoe does this determine the sex of an individual?Egg cells carry X chromosomes. Half the sperm carry X chromosomes and half carry Y chromosomes. The sex of an individual depends on whether the egg is fertilised by an X-carrying sperm or a Y-carrying sperm. If an X sperm fertilises the egg it will become a girl. If a Y sperm fertilises the egg it will become a boy. The chances of these event are equal, which results in approx. equal numbers of male and female offspring.
- 17What can genes have that are different? Give some examples.They can have different alleles (alternative versions).
For example, the gene for eye colour has two alleles: brown and blue. Similarly, the gene for tongue rolling has two alleles: being able to roll your tongue and not being able to. - 18What alleles describes as and what does this mean?They are described as being dominant or recessive:
A dominant allele controls the development of a characteristic even if it is present on only one chromosome in a pair.
A recessive allele controls the development of a characteristic only if a dominant allele is not present, i.e. if the recessive allele is present on both chromosomes in a pair. - 19What is an individual called if both chromosomes in a pair contain the same allele of a gene?The individual is described as being homozygous for that gene or condition.
- 20What is an individual called if the chromosomes in a pair contain the different alleles of a gene?The individual is heterozygous for that gene or condition.
- 21What is the combination of alleles for a particular characteristic called, and what is it called when it is the actual chracteristics?It is called a genotype. For example, the genotype for a homozygous dominant tongue roller would be TT. The fact that this individual is able to their tongue is termed their phenotype (their actual characteristic). Other examples are bb (genotype), blue eyes (phenotype); Ee (genotype), and unattached ear lobes (phenotype)
- 22When a characteristic is determined by just one pair alleles, as with eye colour and tongue rolling, what is this called?It is called monohybrid inheritance.
- 23What do genetic diagrams use?Capital letters for dominant alleles
Lower case letters for recessive alleles - 24How are some disorders caused?Some disorders are caused by a 'faulty' gene, which means they can be inherited (i.e. passed from one generation of a family to the next).
- 25Give some examples of inherited disorders.Red-green colour blindness, where the specialised cells in the eye cannot distinguish between red and green light.
Sickle cell anaemia, which causes red blood cells to become sickle-shaped leading to circulatory problems and oxygen deficiency.
Cystic fibrosis, which causes cell membranes to produce excess thick mucus which blocks airways. It also causes problems with digestion. - 26What is the cystic fibrosis disease due to and what is a carrier?It is due to a recessive characteristic.
Two parents could appear to be completely healthy and unaffected by the disease, but if they both have a recessive allele for the disease one of their children could inherit the disease from them. The parents would be known as carriers. (they do not have the disease themselves because their dominant 'normal' alleles protect them). - 27What happens to a child with cystic fibrosis?An affected child is likely to have a reduced quality of life and a reduced life expectancy. They will need life-long care and medication. However, modern drugs enable many affected people to lead happy and productive lives.
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- GCSE biology (B1) Flashcards on Variation and Inheritance, created by Rebecca Smith on 06/11/2016.
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