7.1 and 7.2 Flashcards
What is meant by the term genotype?
Genetic constitution of an organism
What is meant by the term phenotype?
The expression of this genetic constitution and its interaction with the environment
What are alleles and how do they arise?
Variations of a particular gene that arise by mutation
How many alleles of a gene can be found in diploid organisms?
2 as diploid organisms have 2 sets of chromosomes
- but there may me many alleles of a single gene in a population
Describe the different types of alleles:
Dominant- always expressed
Recessive- only expressed when 2 copies present (homozygous recessive)
Codominant- both alleles expressed/contribute to phenotype
What is meant by the terms homozygous and heterozygous?
Homozygous: alleles at a specific locus are the same
Heterozygous: alleles at a specific locus are different
What do monohybrid and dihybrid crosses show?
Monohybrid- inheritance of one phenotypic characteristic coded for by a single gene
Dihybrid- inheritance of two phenotypic characteristics coded for by two different geness
Explain the evidence from a pedigree diagram which would show that the allele for a named phenotype is dominant:
(named phenotype) parents (n&n) have child (n) without (named phenotype)
So both parents must be heterozygous carriers of recessive allele
- if recessive, all offspring would have named phenotype
Explain the evidence from a pedigree diagram which would show that the allele for a named phenotype is recessive:
Parents (n&n) without (named phenotype) have child (n) with (named phenotype)
So both parents (n&n) must be heterozygous/carriers of recessive allele
What is a sex linked gene?
A gene with a locus on a sex chromosome
Explain why males are more likely to express a recessive X linked allele:
Females (XX) have 2 alleles so only express allele if homozygous recessive/can be carriers
Males (XY) have 1 allele (inherited from mother) so recessive allele always expressed
Explain the evidence from a pedigree diagram which would show that the allele for a (named phenotype) on the X chromosome is recessive:
Mother (n) without (named phenotype) has child (n) without (named phenotype)
So mother (n) must be heterozygous/carrier of recessive allele
Explain the evidence from a pedigree diagram which would suggest that (named recessive phenotype) is caused by a gene on the X chromosome:
Only males tend to have (named recessive phenotype)
Explain the evidence from a pedigree diagram which would show that gene for (named phenotype) is not on the X chromosome:
(named phenotype) father has daughter without (named phenotype)
Father would pass on allele for (named phenotype) on X chromosome so daughter would have (named phenotype)
OR
(named phenotype mother) has son without (named phenotype)
Mother would pass on allele for (named phenotype) on X chromosome so son would have (named phenotype)
Explain how autosomal linkage affects inheritance of alleles:
Two genes located on same autosome
So alleles on same chromosome inherited together
- stay together during independent segregation of homologous chromosomes during meiosis
But crossing over between homologous chromosomes can create new combinations of alleles
- If the genes are closer together on an autosome, they are less likely to be split by crossing over
What is epistasis?
Interacting of non-linked genes where one masks/suppresses the expression of the other
Describe when a chi-squared (X^2) test can be used:
When determining if observed results are significantly different from expected results
Data is categorical
Suggest why in genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios:
Fusion/fertilisation of gametes is random
Autosomal linkage/epistasis/sex-linkage
Small sample size- not representative of whole poopulation
Some genotypes may be lethal
What is the formula for chi-squared?
∑ [ (O-E)^2 ÷ E ]
What is a population?
A group of organisms of the same species in a particular space at a particular time
That can potentially interbreed
What is a gene pool?
All the alleles of all the genes in a population at any one time
What is allele frequency?
Proportion of an allele of a gene in a gene pool
What does the Hardy-Weinberg principle state and what are the conditions under which the principle applies?
Allele frequencies will not change from generation to generation, given:
- population is large
- no immigration/emigration
- no mutations
- no selection for/against particular alleles
- mating is random
What is the Hardy-Weinberg equation?
p^2 + 2pq + q^2 = 1
Use with p + q = 1
