inheritance

• Mendel 1886 cross bred purple pea plants and white pea plants to see how traits are passed down by generations.
• Mendel cross bred peas F1 where all purple flowers (dominant alleles)where as F2 had purple and some white flowers (recessive alleles make a reappearance)
• law of inheritance is the characteristics of an organism are determined by alleles which come in pairs. Only one pair of alleles can be present in a single gamete.
• law of segregation is that there is a 50/50 chance of an organism inheriting a type of allele
• law of independent assortment traits like detached or attached ear lobes, sort independently and don't influence any other traits
• genes have 3 characteristics

  • they can separate and combine
  • they can mutate
  • they code for the production of a specific polypeptide
• a gene is a section of DNA on a chromosome that codes for a specific polypeptide
• an allele are different forms of the same gene
• gene locus is the location of a gene on a chromosome
• homologous pair chromosomes are chromosomes, one maternal and one paternal, with the same gene loci
• genome is the total genetic make up of an organism/cell
• genotype describes the alleles that an organism has and is represented by a single letter for each allele.
• Organisms with homologous chromosomes will have there genotype represented with 2 letters
• phenotype is the appearance of an organism determined by its genotype
• dominant alleles will always be expressed in the phenotype and is represented as a capital letter in the genotype.
• recessive allele will only be expressed in the phenotype if both alleles in the genotype are recessive (2 lowercase letters). recessive alleles are represented in the genotype with lower case letters
• homozygous is if both alleles on each homologous chromosome is the same then that organism is homozygous for that gene. the letters in the genotype will both be capital or lowercase
• heterozygous is when the alleles in the genotype are different. One recessive and one dominant.
• F1 is the first generation of offspring
• F2 is the second generation of offspring
• a carrier is an organism carrying an allele which is not expressed in their own phenotype but can be passed onto offspring
• monohybrid inheritance is the inheritance of one gene (two alleles) from a homologous pair of chromosomes
• co dominance is instead of 1 allele being dominant, both alleles are expressed in the phenotype, neither are dominant. Both alleles are equally expressed and contribute to the phenotype.
• multiple alleles occur when a gene has more than two alleles. an example of this is blood type
• • A+A=A
  • A+O=A
  • A+B=AB
  • B+B=B
  • B+O=B
  • O+O=O
• a pair of homologous chromosomes are sex chromosomes which carry the genes coding for male or female sex. Non sex chromosomes are called autosomes
• XX = homogametic
• XY = heterogametic
• sex linked genes are alleles that are carried on the X chromosome but not on the Y
• Y chromosome is smaller than the X and carries very few genes therefore any recessive alleles carried on the X will be expressed in phenotype.
• examples of sex linked disorders is haemophilia and colour blindness
• Dihybrid inheritance is the inheritance of two genes (four alleles) from different homologous pairs of chromosomes
• at meiosis the pair of homologous chromosomes are separated, one of each pair into one of the two gametes formed. There is however random/ independent segregation of chromosomes so all allele combinations are possible.
• chi squared = (O-E) squared divided by E
• in chi squared if value is larger than critical value you reject null hypothesis. degrees of freedom = number phenotypes -1 (n-1)
• autosomal linkage occurs when 2 different genes occur on the same chromosome. genes on the same chromosome will tend to be inherited together because they move together during meiosis and appear in the same gamete.
• unusual recombinants are expected in autosomal linkage. recombination of DNA occurs when alleles are exchanged as part of cross over in meiosis. The further apart the 2 genes are on the chromosome are higher the chance there is of cross over taking place and the genes being separated.
• epistasis is the phenotypic expression of a gene at one locus alters that of a gene at a second locus. It is the interaction of different gene loci so that the allele of one gene masks or supresses the expression of other genes. 2 genes responsible for the expression of 1 phenotype