Patterns of inheritance Flashcards
What is an allele?
Different versions of a gene
What is a Genotype?
A combination of alleles.
What is a Phenotype?
The physical expression of a Genotype
What is a dominant allele?
Only need 1 allele for it be expressed in phenotype
What is a recessive allele?
Need two recessive alleles for for it to be expressed in phenotype
What does homozygous mean?
When the alleles are the same so either they are both recessive or both dominant
What does heterozygous mean?
When the alleles are different so one is recessive and one is dominant
What type of letter is used to denote a dominant allele?
A capital
What type of letter is used to denote a recessive allele?
A lowercase
What is a genetic cross?
A genetic cross can be drawn to show the probabilities of offspring inheriting different genotypes.
Why are genetic/offspring ratios often different from those expected?
> offspring ratios are a probability - they are not fixed and arise by chance
gametes may not be produced in equal numbers
fertilisation/fusion of gametes is random
small sample
What are the chromosomes’ for a girl?
XX
What are the chromosomes’ for a boy?
XY
What are Co-dominant alleles?
Both alleles are dominant and both are expressed in the phenotype, e.g. AB blood group.
What are the chromosomes for a male?
X Y
What are the chromosomes for a girl?
X X
Which chromosome does a male get from his father?
Y
What chromosome do females get from each parent?
X
What are genes located on a sex chromosome called?
Sex linked genes
Who can fathers pass sex-linked alleles too?
Only Daughters
Who can mothers pass sex linked alleles too?
Sons and Daughters
What chromosome are most sex linked conditions passed via?
X
What are some examples of sex linked conditions?
•colourblindness
• haemophilia
• duchennes muscular dystrophy (DMD)
Why are observed offspring ratios are often not the same as expected ratios?
Fertilisation is random - fusion of gametes is random
Why are males more likely to show a phenotype produced by a recessive allele carried on the X chromosome?
Females could be heterozygous/carriers
For a female both her chromosomes would have to carry the recessive allele.
What does dominant epistasis mean?
Dominant 1st gene masks the expression of the 2nd one
What is recessive epistasis?
If the 1st gene is recessive and isn’t expressed the second cant be.
Define species
A group of organisms which can interbreed and produce fertile offspring
Whats speciation?
Means the development of a new species and it can occur when populations are reproductively isolated in some form.
What is allopatric speciation?
When there is a geographic barrier that separates the populations, like a river or mountain that keeps them from being able to interbreed and share the same gene pool.
What is sympatric speciation?
The speciation happens in the same area, yet there’s something else isolating them such as prezygotic barriers or postzygotic barriers.
What are examples of prezygotic (before zygote can be made) barriers?
> behavioural isolation - different behaviours that can isolate them such as birds having different songs/ different courtship which can prevent the males from attracting the females of other populations.
> temporal isolation - species could breed at different seasons, years, different times.
> habitat isolation - even assuming that organisms live in the same area doesn’t mean their habitats are exactly the same such as one prefers an aquatic environment and one prefers a terrestrial environment.
What are examples of postzygotic (zygote is formed) barriers?
> offspring are unable to reproduce
offspring produced between 2 different species are very weak and do not survive long
interbred offspring are not able to develop in even very early embryonic stags because their is genetic incompatibility
What is bottleneck?
Significant reduction in the size of a population due to environment events or human activities
What is the Chi-Squared test used for?
To determine if there is a significant association between categorical variables.
What is continuous variation?
Traits that can take on a range of values rather than distinct categories.
Define dihybrid
An organisms that is heterozygous for two specific traits
Whats directional selection?
Type of natural selection that occurs when individuals with a certain phenotype are favoured over others
Whats discontinuous variation?
Traits that exhibit distinct categories
What is epistasis?
Where the expression of one gene is affected by one or more other genes.
What is the founder effect?
When a small group of individuals becomes isolated from a larger population.
What is genetic drift?
Random changes in allele frequencies within a population overtime.
What does the Hardy-Weinberg equation show?
Describes the genetic variation in a population at equilibrium. It shows the frequency of a particular allele is the proportion it represents of all the alleles of a gene. Frequency is always less than 1 so always a decimal.
p + q = 1
p^2 + 2pq + q^2 = 1
Whats an isolating mechanism?
Prevents different species’ from interbreeding
What is linkage?
Genes are located close together on the same chromosome to be inherited together during meiosis.
Whats a monohybrid?
Organisms that are heterozygous for a single trait.
Whats sex linkage?
The association of certain genes with the sex chromosomes - X or Y
Whats stabilising selection?
Type of natural selection that favours the average, removing extremes.
Whats variation?
Differences in traits among individuals within a population.
In the Hardy-Weinberg equation what does the p and q stand for?
p = frequency of dominant allele
q = frequency of recessive allele
In the Hardy-Weinberg equation what does the p^2 and q^2 stand for?
Genotype frequencies
How do you use the results of a Chi-squared test?
You compare the calculated Chi-square value to a critical value from the Chi-squared distribution at a specific level of significance usually 0.05. If the calculated value is greater than the critical value, then the results are considered statistically significant, indicating that there is a relationships between the variables being studied.
