3.7.1 Inheritance (Genetics , population , evolution and ecosystems 3.7) 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 - arise by mutation
How many alleles of a gene can be found in a diploid organism
- 2 as dipole is organisms have 2 sets of chromosomes
• but there may be many alleles of a single gene in a population
Describe the e different types of alleles
Dominant alleles : Always expressed
Recessive alleles : Only expressed when 2 copies present ( homozygous recessive )
Codominant alleles : Both alleles expressed
What is meant by the term 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 cross = inheritance of one phenotypic characteristics coded for by a single gene
- Dihybrid cross = inheritance of two phenotypic characteristics coded for by two different genes
Explain the evidence from a pedigree diagram which would show that the allele for [ named phenotype ] is dominant
• [Named phenotype] parents [n&n] have child [n] without [named phenotype]
• So both parents [n&n] must be heterozygous/ carriers of recessive allele
- if it were recessive , all offspring would have [ named phenotype]
Explain the evidence from a pedigree diagram which would show that the allele for [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 => only express recessive allele if homozygous recessive / can be carriers
- Males (XY) have 1 allele -> recessive allele always expressed
Explain the evidence from a pedigree diagram which would show that the allele for [named phenotype ] on the X chromosome is recessive
• mother [n] without [named phenotype] has a child [n] with [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 the gene for [named phenotype] is not on the X chromosome
• [named phenotype] father [n] has daughter [n] without [named phenotype]
• father [n] would pass on allele for [named phenotype] on X chromosome so daughter [n] would have [named phenotype]
explain how autosomal linkage affects inheritance of alleles
- two genes located on same autosome ( non - sex chromosome )
- so allele 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 autosomes , they’re less likely to be split by crossing over
