Inheritance Flashcards
What is a gene?
A gene is a section of a molecule of DNA and codes for a specific protein
What does a DNA molecule look like?
A DNA molecule is two strand coiled to form a double helix, being linked by a series of base pairs
What are the complimentary base pairs?
- adenine and thymine
- cytosine and guanine
What is a dominant allele?
An allele which is always expressed
What is a recessive allele?
An allele only expressed if both alleles are recessive (homozygous)
What does homozygous mean?
Having two of the same alleles
What does heterozygous mean?
Having two different alleles
What is a phenotype?
The physical characteristics an organism has
What is a genotype?
A set of alleles
What is codominance?
It’s what happens when both alleles are expressed in the same phenotype
How do you read a family pedigree?
The squares are male
The circles are female
If the shape is coloured in, that family member is affected by the genetic trait
Why is a family pedigree useful?
It shows the pattern of inheritance of a genetic trait
What is the sex of a person controlled by?
A pair of chromosome:
XX is female
XY is male
Why are heterozygous individuals often called carriers?
Because they carry the allele for the recessive characteristic so do not show the trait, but can pass it on to their offspring
When does mitosis occur?
In growth, repaid, cloning and asexual reproduction
What does the division of a diploid cell by mitosis produce?
Two daughter cells which contain identical sets of chromosomes
What does the division of a cell by meiosis produce?
Four daughter cells, each with half the number of chromosomes - resulting in the formation of genetically different haploid cells
What produces genetic variation in offspring?
Random fertilisation
How many chromosomes are there in diploid and haploid human cells?
Haploid: 23
Diploid: 46
What is a mutation?
A mutation is a rare, random change in a gene that can be inherited. It can be neutral, beneficial or harmful.
Describe the process of evolution by means of natural selection
- a mutation occurs
- if the mutation is beneficial, the animal will survive longer and reproduce more
- some offspring will inherit the mutation
- the offspring will have a better chance of survival, so they’ll live longer and reproduce more
- over long periods of time, the process is repeated and gradually the mutation becomes a common gene
What happens if bacteria experience mutations?
Bacteria experience mutations which can mean they’re no longer affected by a certain antibiotic. If they evolve to become resistant to drugs, they are difficult to control
How can the chances of mutation be increased?
- by exposure to ionising radiation (eg gamma rays and X-rays)
- by some chemical mutagens (eg chemicals in tobacco)
What does the nucleus of a cell contain?
It contains chromosomes on which genes are located
