Genotype, Phenotype + Inheritance Flashcards
What is the meaning of hemizygous?
Only one allele of a gene is present
What is the meaning of homozygous?
Two alleles of gene are the same
What is the meaning of heterozygous?
Two alleles of a gene are different
What are the different modes of inheritance?
dominant - determines the phenotype in a heterozygous
recessive - the non-dominant allele in a heterozygote > both alleles need to be recessive for trait to appear
What is a codominant allele?
Example
There is an equal influence of two alleles on the phenotype
e.g. blood type
What is polygenic inheritance?
Example
Where phenotypes are affected by multiple genes
Continuous trait
e.g. skin colour
What is a pedigree chart?
A diagram which shows genetic information from a family using standardised symbols
2 purposes of a pedigree chart
- Determines the pattern of inheritance for a given trait
- Discovers whether the gene is location on a X or Y chromosome
What is genotype?
Genetic description f a person
What is phenotype?
Examples
Observable characterised of a person
e.g. hair,eye colour, expression of enzyme
As a result of genotype interaction with environment
What is an allele?
Different version of the same gene on the same position of a chromosome
What symbols are used for males, females + unknown sex in a pedigree chart?
Affected vs unaffected
Males - square
Females - circle
Unkown - diamond
Unaffected - white
Affected - black/filled in
What is the symbol for carrier/heterozygous recessive allele in pedigree charts?
Half filled
Black dot
How are twins represented on a pedigree tree?
Connected by two diagonal lines
Identical twins have one horizontal line between them too
Example of autosomal dominant disease
Achondroplasia
Ehlers-Danlos syndrome
Marfan’s syndrome
Huntington’s disease
Example of autosomal recessive disease
Cystic fibrosis
Albinism
PKU
Sickle cell anaemia
Xeroderma pigmentosum
Must be homozygous
Example of X-linked recessive disease
Haemophilia A and B
Fragile X syndrome
Duchene muscular dystrophy
How do X-linked recessive diseases affect genders + offspring?
Affected males:
- have heterozygous daughter as can only pass on X chromosome o daughter
- cannot pass on to sons
- heterozygous carrier mother (at least)
Affected female:
- have affected father
- carrier mother
Parents of affected female of X linked recessive disease
Affected father
Carrier (or affected) mother
Parents of affected male of X linked recessive disease
Heterozygous carrier mother (or affected)
Who is affected by Y-linked dominant pedigree
Only men
What does monogenic inheritance mean?
Example
When phenotype is influenced by one gene
Discontinuous trait
e.g. widow’s peak
What is linkage?
Genes don’t show independent assortment during meiosis in metaphase
What does the location of genes on chromosome have to do with their inheritance?
Genres that are closer together are more likely to be inherited together - tightly linked
What is penetrance?
Describe whether there is clinical expression of a phenotype in a person
% of people with a genotype that show a symptom
What is expressivity?
Describe the different in clinical prevention between two people with the same genotype
The severity of disease in different people
What are the 5 patterns of Mendelian inheritance?
Autosomal recessive
Autosomal dominant
X linked dominant
X linked recessive
Y- linked
What is a pattern of non-Mendelian inheritance?
Mitochondrial inheritance
Controlled by single genes coed for by mitochondrial genes
What are autosomes?
Non-sex chromosomes
What are the features of a X linked dominant trait on a pedigree chart?
No generations are skipped
Affected sons have affected mothers
Affected fathers have affected daughters
What are the features of a X linked recessive trait on a pedigree chart?
Affected daughters have affected fathers
Affected mothers have affected sons
What is the chance of offspring being affected by autosomal recessive disease?
25%
How are mitochondrial diseases passed down?
Maternal line
What is Klinefelter syndrome?
Where boys are born with an extra X chromosome
47 XXY
What is the karyotype of Klinefelter syndrome?
47, XXY
