Inheritance Flashcards
Define genotype.
The genetic constitution of an organism.
(eg.BB, Bb, bb for eye colour)
Define phenotype.
The expression of the genetic constitution and its interaction with the environment.
(eg. brown eyes)
Define allele.
Different versions of the same gene.
Define dominant.
The dominant allele is always expressed.
(eg. BB = blue eyes / Bb = blue eyes)
Define recessive.
The allele is only expressed if it is homozygous recessive.
(eg. bb = brown eyes)
Define co-dominant.
Both alleles are expressed in the phenotype.
eg. (using superscripts)
C^R C^R = red flowers
C^W C^W = white flowers
C^R C^W = pink flowers
Define homozygous.
Both alleles at a specific locus on each homologous chromosome are the same.
BB - homozygous dominant
bb - homozygous recessive
Define heterozygous.
Both alleles at a specific locus on each chromosome are different.
Define monogenic inheritance.
The characteristic inherited is controlled by a single gene.
Define dihybrid inheritance.
The inheritence of two different characteristics controlled by two different genes (on different chromosomes).
Eg. pure breeding pea seeds
- Yellow and round = YYRR (both dominant)
- Green and wrinkled = yyrr (both recessive)
Any of these alleles can combine due to independent segregation.
Draw a 2x2 punnet square of parent genotypes to find gametes.
SO possible gametes:
- YR, YR, YR, YR
- yr, yr, yr, yr
THEN draw 4x4 punnet square to find offspring genotypes:
16 - YyRr
THEN work out the offspring phenotypes:
YyRr = yellow and round
What does a dihybrid cross of pure breeding seeds result in?
All the F1 generation is heterozygous for both seed colour and shape.
What is the phenotypic ratio for the F2 generation of pure breeding seeds from a dihybrid cross?
9 : 3 : 3 : 1
Define multiple alleles.
3 or more possible alleles for one individual trait within a population.
Eg.
Blood groups = A /B / AB / O
I^A and I^B are co-dominant
I^O is recessive
Define autosomal linkage.
2+ genes which are located on the same autosome
(ie. on the same single non-sex chromosome)
What happens to genes that are autosomally linked during meiosis I?
- They stay together during independent segregation.
- There is no crossing over so linked genes stay together.
- Linked genes pass onto gametes and offspring together.
- A higher proportion of offspring will have the parents’ genotype and phenotype as the autosomally linked genes are inherited together.
What is the phenotypic ration for autosomal linkage?
3:1
(ALWAYS)
Define sex-linked.
A gene whose locus is on a sex chromosome.
Why are genes more likely to be linked to the X chromosome?
- The X chromosome is larger.
- Some genes are found on sections on the X chromosome which are not present on the Y chromosome.
What is the genotype for males and females?
Males = XY
Females = XX
Why do more males have sex-linked disorder?
- Males = XY
- The can’t be heterozygous.
- SO they will always express the recessive X-linked allele if one copy is present.
Define epistasis.
The interaction of non-linked genes where one masks the expression of the other.
‘epi’ = on top of
‘stasis’ = standing
What is the chi-squared (X^2) test?
A statistical test used to find out whether the difference between the observed vs expected data is due to chance.
What is the limitation of a chi-squared test? And what can be done to combat this?
- The sample may be unrepresentative of the whole population.
- Use a larger sample size / statistical analysis
When do we use the chi-squared test?
- Categorical data
- Absolute numbers in data
What does it mean if the calculated value of chi-squared is larger than the critical value at P = 0.05?
- The results are significant.
- There is less than 5% probability that the differences were due to chance.
- Reject the null hypothesis.
What does it mean if the calculated value of chi-squared is smaller than the critical value at P = 0.05?
