Cell Division & Genetics - Part 2 Flashcards
Much of our understanding of inheritance comes from the work of an Austrian monk called Gregory Mendel. During his investigations he noticed that some characteristics were more common than others and that they were more likely to be found in the offspring. What did he call these two types of characteristics?
Dominant and recessive
What is the term used to describe the letters describing the characteristics?
Genotype
What is the term used to describe the outward appearance of the genotype?
Phenotype
What is genetics?
Genetics is the study of inheritance i.e. how characteristics are passed from one generation to the next.
How many chromosomes are in each human cell?
46
What are chromosomes?
Chromosomes are located in the nucleus of cells and carry the genetic material in short sections called genes.
What is a gene?
A gene is a short section of chromosome that codes for a particular characteristic, e.g. eye colour
What is an allele?
An Allele is a particular form of a gene. For example, brown eyes and blue eyes are different alleles of the eye colour gene.
What does homozygous mean?
The term homozygous is used to describe where both alleles of a gene are the same. For example, in eye colour both alleles are for brown eyes.
What does the term heterozygous mean?
Heterozygous is used to describe alleles of a gene that are different. For example, in eye colour one allele is for brown eyes and the other is for blue eyes.
What is the genotype?
The genotype is paired symbol showing the allele arrangement in an individual.
What is the phenotype?
The phenotype is the outward appearance of an individual. In other words, the characteristics we can see.
What is the name given to parent plants that only produce one type of offspring?
Pure breeding
What is meant by a dominant allele?
In the heterozygous condition the dominant allele overrides the non-dominant (recessive) allele. In other words, it is always expressed (shows its effects)
What is a recessive allele?
A recessive allele is dominated by the dominant allele - it only shows itself in the phenotype if there are two recessive alleles.
What is the complete set of chromosomes known as?
A karyotype
What are Punnett Squares?
Punnett Squares are diagrams that are used to show the possible outcomes of genetic crosses. They can tell us the probability of a certain genotype being found in offspring.
Explain why some genetic disorders are sex linked.
The X and Y chromosomes are not only responsible for sex determination, they also have the genes that code for conditions such as haemophilia and red/green colour blindness. These are referred to as sex linked.
Both cases the normal gene is dominant and these conditions are recessive and carried on the X chromosome. This is particularly important in males as they have only one X chromosome, therefore any recessive allele carried on this chromosome will show its effect in the phenotype, in other words the males will suffer from the condition. The female usually has a normal allele to mask the affect of the defect one and so females rarely suffer from sex linked conditions.
What is the term used to describe a girl who is heterozygous for colour blindness?
A carrier
