Year 12 Biology Module 3: The Species Outcomes covered: 3.8, 3.9, 3.10, 3.11
Autosomal Dominant Inheritance Dominant gene located on 1 of the autosomes Letters used are upper case ie BB or Bb Affected individuals have to carry at least 1 dominant gene (heterozygous or homozygous) Passed onto males and females Every person affected must have at least 1
parent with the trait Does not skip generations E.g. Huntingtons disease, Marfan syndrome Autosomal DominantMarfan syndrome Autosomal Recessive Inheritance
The recessive gene is located on 1 of the autosomes Letters used are lower case ie bb Unaffected parents (heterozygous) can produce affected offspring (if they get both recessive genes ie homozygous) Inherited by both males and females Can skip generations If both parents have the trait then all offspring will also
have the trait. The parents are both homozygous. E.g. cystic fibrosis, sickle cell anaemia, thalassemia Autosomal Dominant/ Recessive Problems Cross a pure breeding, black coated guinea pig with a pure breeding, white coated guinea pig. Given that, in
guinea pigs, black coat colour is dominant to white coat colour, determine the genotypes and phenotypes of the first and second generation offspring. Incomplete dominance In a heterozygous organism, neither
gene is dominant, both genes are expressed equally Capital letters used for both alleles Snap dragons- red = RR, white= WW, pink = RW Cows- brown = BB, white= WW, roan=BW Incomplete dominance
Incomplete dominance problems In Andalusian chickens, the black Andalusian character is incompletely dominant to the white-splashed Andalusian character. The heterozygous condition produces blue Andalusian chickens.
Determine the genotypes and phenotypes of the F1 and F2 generations if a pure breeding, black Andalusian is crossed with a pure breeding, white-splashed Andalusian. Co- dominance Occurs when alternative alleles are
present in the genotype and fully observed in the phenotype E.g. ABO blood grouping system, where a single gene locus features multiple alleles- IA, IB, and i. Individuals carrying alleles for both A and B express both in the phenotype AB.
Co- dominance Genotype IA IA or IAi IB IB, or IBi IAIB ii Phenotype
group) A B AB O (blood
Sex linked inheritance Genes are carried on the sex chromosomes (X or Y) Sex-linked notation
XBXB normal female XBXb carrier female XbXb affected female XBY normal male XbY affected male
Sex linked inheritance Dominant Dominant gene on X chromosome Affected males pass to all daughters and none of their sons Genotype= XAY If the mother has an X- linked dominant trait
and is homozygous (XAXA) all children will be affected If Mother heterozygous (XAXa) 50% chance of each child being affected E.g. dwarfism, rickets, brown teeth enamel. Sex linked dominant disorders
Sex linked dominant problems The barred pattern of chicken feathers is inherited by a pair of sex linked genes, B for barred, b for no bars. If a non-barred female is mated to a barred male, a)What will the proportion and appearance of
the offspring? What will be the appearance and proportion of the progeny produced by mating an Fl male with an Fl female? Sex linked Inheritance Recessive Gene located on the X chromosome
More males than females affected (males inherit X from mother) Females can only inherit if the father is affected and mother is a carrier (hetero) or affected (homo) An affected female will pass the trait to all her sons Daughters will be carriers if father is not affected Males cannot be carriers (only have 1 X so either
affected or not) Can skip generations E.g. colour blindness, haemophilia, Duchene muscular dystrophy Sex linked recessive problem Red-green colour blindness in men is caused by
the presence of a sex-linked recessive gene c, whose normal allele is C. a) Can two colour blind parents produce a normal son? b) Can they produce a normal daughter? c) Can two normal parents produce a colourblind son or daughter? d) Can a normal daughter have a colourblind father or
mother? e) Can a colourblind daughter have a normal father or mother? Sex linked Inheritance in Drosophila General Pedigree
refer to NOB2 (new ed) pages 328-332 Autosomal Dominant Pedigree Look for: Trait in every generation
Once leaves the pedigree does not return Every person with the trait must have a parent with the trait Males and females equally affected
Unaffected parents can have affected children Affected person must be homozygous Males and females affected equally Autosomal recessive
Sex linked Dominant pedigrees Look for: More males being affected Affected males passing onto all daughter (dominant) and none of his sons
Every affected person must have an affected parent Sex linked recessive pedigrees More ales being affected Affected female will pass onto all her sons
Affected male will pass to daughters who will be a carrier (unless mother also affected) Unaffected father and carrier mother can produce affected sons Sex linked recessive
Questions to complete Complete the following: Biochallenge pg 334, ques 2 Review ques pgs 335-338 Ques 6,7,8, 9, 10, 11, 12, 13, 14, This powerpoint was kindly donated to www.worldofteaching.com
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