20 - Patterns of Inheritance and Variation Flashcards
How is closeness of two linked genes on a chromosome linked to the number of recombinant offspring?
More closely linked genes means less separation and so less recombinant offspring
What is a phenotype?
Physical characteristics of an organism
What is a genotype?
Genetic makeup of an organism
What 2 things affect an organism’s phenotype?
Genotype and environment
What is it called when a characteristic is codes for by multiple genes?
Polygenic
What type of characteristics tend to be polygenic?
Ones which vary within a range, such as height
What is continuous variation?
A characteristic that can take any value within a range
What is discontinuous variation?
A characteristic that can only result in certain values
What does it mean if something is monogenic?
Controlled by only 1 gene
What type of characteristics tend to be monogenic?
Ones which exhibit discontinuous variation
What are the 3 things which affect genotype?
- Sexual reproduction 2. Gene mutations 3. Chromosome mutations
What 2 characteristics do all mutations which take place during gamete formation have?
- Persistent (passed through many generations) 2. Random (so not directed by need)
When do chromosome mutations occur?
During meiosis
What is polyploidy?
A condition in which an organism has more than two complete sets of chromosomes
What type of organism tends to be polyploidy?
Many cultivated plants
What are 3 ways in which sexual reproduction can cause genetic variation?
- Allele shuffling during crossing over 2. Independent assortment 3. Random fertilisation, where any male gamete can fertilise any female gamete
What is etiolation?
Where plants grow long and spindly due to a lack of light
What is chlorosis?
The yellowing of leaves due to a lack of Magnesium ions (Mg2+)
What are 3 examples of environmental factors which can affect phenotype?
- Diet in humans 2. Etiolation 3. Chlorosis
What is a dominant allele?
An allele which will always be expressed when present
What is a recessive allele?
One which will only be expressed when there are 2 copies present
What does it mean if alleles are codominant?
Both are expressed in the phenotype, which becomes sort of a hybrid of the traits coded for by both
What is a dihybrid?
A hybrid that is heterozygous for alleles of two different genes
How do you write the first and second generations when doing homozygous genetic crosses?
First is F1, second is F2
What do you call the parental generation when doing a homozygous genetic cross?
F1 generation
What is a gene locus?
Location of a gene on a chromosome
What are the 3 golden rules of monohybrid crosses?
- Homozygous dominant and homozygous recessive give 100% heterozygous offspring 2. Two heterozygous give a 3:1 ratio of phenotypes 3. Heterozygous and homozygous recessive give a 1:1 ratio of phenotypes
What is a test cross?
Crossing an organism with a heterozygous genotype with one with a homozygous recessive genotype
What would you use a test cross for?
Determining the genotype of an individual showing a dominant characteristic
What happens when multiple (i.e. more than 2) possible alleles are present for a gene?
Only 2 can be present in the offspring’s genotype
Which gamete determines the sex of the offspring?
Sperm, depending on whether it carries a Y allele or not
What does it mean if a gene is sex linked?
Located on one of the sex chromosomes
What is an autosome?
Any chromosome that is not a sex chromosome
What is autosomal linkage?
Gene loci present on the same autosome that are often inherited together
What are 3 examples of sex-linked medical conditions?
- Haemophilia 2. Colour blindness 3. Duchenne’s muscular dystrophy
What is dihybrid inheritance?
The inheritance of two characteristics which are controlled by different genes
What are 2 reasons the actual ratio of phenotypes may differ from the theoretical one?
- Fertilisation of gametes is a random process, so few chance events can lead to a skewed ratio 2. Genes being studied are on the same autosome
What is epistasis?
When one gene masks or suppresses the expression of another
Why are sex-linked recessive conditions more likely to appear in men?
As there is no dominant allele on the X chromosome
What is the usual phenotypic ratio you would expect for a dihybrid cross?
9:3:3:1
What happens to the phenotypic ratio of a dihybrid cross if there is autosomal linkage?
It becomes more like a monogenic one (3:1)
What is the Chi Squared test used to measure?
The size of the difference between the observed and expected results, as well as whether these differences are significant
How do linked genes tend to be inherited?
Together, unless they are separated by chiasmata
What are recombinant offspring?
Recombinant offspring are those that have an arrangement of alleles on the chromosome that was not present in either parent
What are the 2 forms of epistasis?
Dominant and recessive epistasis
When would recessive epistasis occur?
If the presence of 2 recessive alleles led to a lack of something
What is inbreeding?
Mating between closely related individuals
What is outbreeding?
The breeding of distantly related individuals of a species
