5951831
Genetic Inheritance
- Definitions
- Gene- The smallest unit of heredity
corresponding to section of DNA that codes
for a specific mRna that is, a section of DNA
located between a start codon and a stop
codon
- Chromosome- The structures that
are formed within the nucleus of a
cell by the super-collided DNA - 46
chromosomes (23 pairs of
homologous chromosomes) 44 =
autosomes 2 = sex chromosomes
- Locus- the specific point at a
chromosome where a gene is located
- Allele -Two matched genes at same
location (locus)on chromosome
- Homozygous- If two alleles
code for same trait (FF, ff)
- Heterozygous-If two
alleles different (Ff)
- Genotype-The genetic composition
of an individual (ff,FF,Ff)
- Phenotype – The physical expression
of a genotype (Brown hair)
- Dominant - If allele masks or suppresses the expression of the
other allele it is said to be dominant (represented by capital letter)
- Recessive-The allele masked is
said to be recessive (represented
by lowercase letter)
- Gene- The smallest unit of heredity
corresponding to section of DNA that codes
for a specific mRna that is, a section of DNA
located between a start codon and a stop
codon
- Autosomal Dominant
- Genes that will dominant a recessive
gene (FF, Ff - phenotype will show)
- Normal skin pigment, freckles, ability to roll tongue.
normal arches, dimples, unttached earlobs (FF,Ff)
- Normal skin pigment, freckles, ability to roll tongue.
normal arches, dimples, unttached earlobs (FF,Ff)
- Genes that will dominant a recessive
gene (FF, Ff - phenotype will show)
- Autosomal
Recessive
- Gene that will only show with two
homozygous recessive gene
- Albinsm, No freckles, no tongue
roll,no dimples, flat feet, attached
earlobes (ff)
- Albinsm, No freckles, no tongue
roll,no dimples, flat feet, attached
earlobes (ff)
- Gene that will only show with two
homozygous recessive gene
- Sex-Linked
Inheritance
- Inherited traits determined by genes on sex
chromosome • A gene found only on
X-chromosome = X-linked • A gene found only on
Y-chromosome = Y-linked • If recessive not masked
– so will be expressed in males
- If recessive not masked –
so will be expressed in
males - Color
blind,haemophilia
- If recessive not masked –
so will be expressed in
males - Color
blind,haemophilia
- Inherited traits determined by genes on sex
chromosome • A gene found only on
X-chromosome = X-linked • A gene found only on
Y-chromosome = Y-linked • If recessive not masked
– so will be expressed in males
- Multiple Allele
Inheritance
- Some genes exhibit more
than two allele forms e.g.
blood group
- Ia, Ib are co-dominant; i is
recessive
- You can be blood group A, B, O or
AB
- You can be blood group A, B, O or
AB
- Ia, Ib are co-dominant; i is
recessive
- Some genes exhibit more
than two allele forms e.g.
blood group
- Incomplete
Dominance
- Both alleles expressed in heterozygous to
produce a different phenotype to either
homozygous trait, often an intermediate
- inheritance of hair texture, flower colours
– CC is curly hair cc is straight hair – Cc is
wavy hair
- inheritance of hair texture, flower colours
– CC is curly hair cc is straight hair – Cc is
wavy hair
- Both alleles expressed in heterozygous to
produce a different phenotype to either
homozygous trait, often an intermediate
- Polygenic Inheritance
- Some traits require
several gene pairs
- Skin colour based on three gene pairs,
each with 2 alleles Phenotype is
continuous from very fair to very dark
- Skin colour based on three gene pairs,
each with 2 alleles Phenotype is
continuous from very fair to very dark
- Some traits require
several gene pairs
- Genetic
Diseases
- Cystic Fibrosis – autosomal recessive • Sickle cell
anaemia- co-dominance • Haemophilia- X-linked
recessive • Down syndrome - Trisomy 21 –
chromosomal abnormality
- Cystic Fibrosis – autosomal recessive • Sickle cell
anaemia- co-dominance • Haemophilia- X-linked
recessive • Down syndrome - Trisomy 21 –
chromosomal abnormality
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