2.13 Genes and Inheritance Flashcards
2.13 i) Know the meaning of the terms: gene, allele, genotype, phenotype, recessive, dominant, incomplete dominance, homozygote and heterozygote. ii) Understand patterns of inheritance, including the interpretation of genetic pedigree diagrams, in the context of monohybrid inheritance.
What is a gene?
a sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain
What is an allele?
- a different version of a gene found at the same locus
- different alleles have slightly different base sequences, which code for versions of the same characteristic (e.g. eye colour)
What is a genotype?
the alleles a person has
What is a phenotype?
the characteristics displayed by an organism
What is a recessive allele?
an allele that is only expressed (the effect is only shown) if the other allele of the pair is identical
What is a dominant allele?
an allele that is always expressed (the effect is always shown) even if there is only one copy)
What is incomplete dominance?
when the trait from a dominant allele is not completely shown over the trait produced by the recessive allele, so both alleles influence the phenotype
What is a homozygote?
an organism with two identical alleles of a particular gene
What is a heterozygote?
an organism that has two different alleles of a particular gene
What is a locus?
the position of a gene on a chromosome
What are homologous chromosomes/pairs?
similar chromosomes, one from the father one from the mother (humans have 22 pairs of homologous chromosomes and one pair of sex chromosomes)
What is a carrier?
a person with a heterozygous genotype for a genetic disease where the disease causing allele is recessive (they have the recessive allele but not the disease), so they can pass the disease causing allele to their children
What is an example of incomplete dominance?
the flower colour in snapdragons: the dominant allele causes red coloured flowers and the recessive allele causes white coloured flowers, so heterozygotes are pink (a mix)
How to lay out a genetic cross to get full marks:
- clear punnet square
- letter designation explained
- gametes from the mother and the father labeled
- state the genotype and phenotypes of the offspring
- identify the fraction, decimal, or percentage of offspring required
