Genotype, phenotype, inheritance part 1 Flashcards
What is a phenotype?
Observable characteristics of an individual resulting from the interaction of its genotype with the environment
How is a genotype presented as a phenotype?
Genes on chromosomes in the nucleus are translated to proteins in the cytoplasm which give rise to a phenotype
What is the genotype?
Genetic makeup - sum total of genes carried within an organism
What does the phenotype rise from?
Interaction of its genotype with the enivronment
What environmental factors can alter the phenotype?
Environmental: radiation, lifestyle (e.g. activity, diet), mutagens, chemicals
Can also include diseases: heart disease, infection, cancer, cystic fibrosis, diabetes
Either interact with genotype to affect phenotype or alter phenotype directly
How many genes does a human have?
Around 25,000
How many alleles of a gene does a person have?
Two alleles of a gene
What is an allele?
Alternative form of the same gene at the same position on a chromosome
Homozygous
The two alleles of a gene are the same e.g. AA
Heterozygous
The two alleles of a gene are different e.g. Aa
What does hemizygous mean?
Only one allele of a gene (only the X chromosome- males are XY and one X chromosome in female is silent)
Explain each inheritance pattern (2)
Dominant - dominant allele in heterozygosity determines the phenotype
Recessive - non dominant allele does not influence phenotype unless homozygous
What is codominance?
Equal influence of two alleles on a phenotype- neither allele masks the expression of another
Give an example of co-dominance
Human blood types
A and B blood groups are codominant
What gene codes for the antigens on blood cells?
Isoglutamine
State the 4 modes of inheritance
Autosomal (non sex chromosome)
Sex linkage (gene on X or Y)
Mitochondrial
Polygenic
3 types of sex linked inheritance
X-linked recessive
X-linked dominant
Y-linked
how are genetic traits usually studied in humans and why?
Usually by reconstructing a pedigree in families because it is ethically impossible to do experiment on humans by breeding them
What shape and colour are affected and unaffected males and females in a pedigree tree?
Unaffected male - white square
Affected male - black square
Unaffected female - white circle
Affected female - black circle
How is a carrier represented in a pedigree tree?
Square/ circle half black half white
Or a dot in the middle
Representation of an unknown sex in a pedigree tree
Diomond
What does III.17 mean (for example) on a pedigree tree?
Third Generation,
17 people across from left to right
How are males and females affected by autosomal inheritance
Males and females equally affected - not sex-linked inheritance
How are heterozygous and homozygous individuals affected by autosomal recessive inheritance?
Heterozygous will be unaffected
Homozygous will be shown in phenotype
What is the chance of two heterozygous people having affected offspring in autosomal recessive inheritance?
25% chance of having affected offspring
How does autosomal dominant affect heterozygous and homozygous?
Heterozygous - affected as only need one copy of gene
Homozygous - rarely found in this state as it is more lethal
What is the chance of two heterozygous people having affected offspring in autosomal dominant inheritance?
50% change of having affected offspring
Which autosomal inheritance skips and doesn’t skip a generation?
Recessive can skip generations
Autosomal dominant cannot skip a generation - affected individual in every generation
What is the incidence of carriers in a population?
1 in 50
In X-linked recessive inheritance, what daughters will affected males have?
Affected males will always have heterozygous daughter- one X from mother and one X from father so disease always passed to daughter
In X-linked recessive inheritance, what parents would an affected female have?
An affected father and (at least) a carrier mother - recessive disease so need 2 copies of affected gene
In X-linked recessive inheritance, what does the mother of an affected male have to be?
At least heterozygous carrier - Y is inherited from father so only one X gene needed from mother
What are co-dominant alleles?
When neither allele in a heterozygous is dominant - both alleles are fully expressed, creating a new phenotype
