Inheritance Flashcards
(24 cards)
What is a gene?
Sequence of bases on DNA molecule coding for protein (polypeptide) which results in characteristics e.g. a gene for eye colour
What is an allele?
Different versions of same gene coding for variants of a characteristic represented by letters e.g. B = brown eyes b = blue eyes
What is a genotype?
Organism’s genetic makeup, its alleles e.g. BB, Bb, or bb
What is a phenotype?
Organism’s physical characteristics determined by its genotype and environment
What is a dominant allele?
Allele thats always expressed in phenotype even when only 1 copy is present in genotype (shown with uppercase letter)
What is a recessive allele?
Allele thats only expressed when homozygous in genotype (2 copies present) and is masked by dominant allele (shown with lowercase letter)
What is a gene locus?
Specific position of a gene on a chromosome
What is a homozygous organism?
Organism with 2 identical alleles for a trait
What is a heterozygous organism?
Organism with 2 different alleles for a trait
What are the differences of humans and gametes?
Humans are diploid organisms almost always having 2 copies of each gene meaning they have 2 alleles for every characteristic
gametes (sex cells) are haploid meaning they have 1 allele per gene
What does monohybrid inheritance involve?
Transmission of 1 gene from parents to their offspring
What is an F1 generation?
- offspring from a cross between individuals with homozygous dominant and homozygous recessive genotypes
- all offspring will be heterozygous inheriting recessive allele from 1 parent and dominant allele from the other
- offspring will therefore all express dominant trait in their phenotype
What is an F2 generation?
- offspring from a cross between 2 heterozygous F1 individuals
- results in offspring exhibiting 3:1 ratio of dominant to recessive phenotypes
What is a punnet square and what’s its purpose?
Represents a monohybrid cross in a grid format
allows you to predict genotype and phenotype ratios
Outline the stages of using a punnet square?
1) state phenotypes of 2 parents
2) assign genotypes of parents (e.g. GG, Gg or gg)
3) state gametes of parents (e.g. G or g)
4) use Punnett square to show all offspring genotypes that could be produced from random fertilisation of parental gametes
5) state proportion of each genotype among offspring as a ratio or percentage
6) state proportion of each phenotype among offspring
What is codominance?
When 2 different alleles are equally expressed in organism’s phenotype and both alleles share equal dominance
means both alleles are visible in organism’s observable characteristics leading to phenotype thats a mixture of both alleles rather than just one
How is codominance shown in genetic diagrams?
- uppercase letter used to signify gene (e.g. C for colour)
- superscript uppercase letters indicate alleles (e.g. CR, CW for colouration)
- avoid lowercase letters to prevent implication of recessiveness
What are multiple alleles?
Genes existing in more than 2 allelic forms
however an individual can only have 2 alleles of a specific gene at any 1 time
What is the A, B and O blood group controlled by?
Immunoglobulin or I gene
What are the alleles in the blood group system?
IA and IB are codominant as both expressed when inherited together
IO allele is recessive
Whats the phenotype and antigen present for IAIA or IAIO?
Blood type A
A
Whats the phenotype and antigen present for IBIB or IBIO?
Blood type B
B
Whats the phenotype and antigen present for IAIB?
Blood type AB
A and B
Whats the phenotype and antigen present for IOIO?
Blood type O
none
