topic 7

• Homozygous recessive


  When genotype is 2 recessive alleles
• Homozygous dominant


  When genotype is 2 dominant alleles
• Heterozygous


  When genotype is 2 different alleles
• Genotype


  the genetic constitution of an organism.
• Phenotype


  the expression of genetic constitution due to its environment
• Allele


  Different variants of the same gene
• Codominance


  both alleles for a gene are fully expressed in the phenotype
• What did Gregor Mendel discover about inheritance?

  Certain traits can be dominant or recessive, recessive traits may not show but can be passed on.
• Is the haemophilia allele recessive or dominant?

  Recessive
• Why are men more likely to have a sex linked than women?

  - men have one allele wheras females need two recessive alleles
• What is a genetic cross used for?

  To predict the outcome of offspring based on parent's genotype.
• What is meant by 'multiple alleles'?

  More than two alleles, of which only 2 may be present at loci of someone's homologous chromosomes.
• What is monohybrid inheritance?


  Inheritance of a characteristic controlled by a single gene.
• What is the position of a gene on a particular DNA molecule known as?

  Locus
• What is dihybrid inheritance?

  Two characters, determined by two different genes located on different chromosomes are inherited
• Give an example of dihybrid inheritance

  Gregor Mendel investigating seed shape and seed colour of a pea plant
• How did Gregor Mendel investigate dihybrid inheritance?

  Carried out a cross between 2 pure breeding types of plants:

  
  

  - One always produced round-shapes, yellow seeds other always produced wrinkle-shaped, green seeds.
• What is the ratio of a dihybrid cross?

  9:3:3:1?
• In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. why?

  - small sample size

  -fertilisation of gametes is random

  -genes are linked epistasis

  - lethal allelesSee an expert-written answer!We have an expert-written solution to this problem!
• What is sex linkage?


  Genes that are located on either an X or Y chromosome
• What is autosomal linkage?

  Gene loci present on the same autosome that are often inherited together
• What are autosomes?


  Chromosomes 1-22
• how is it possible to get 4 phenotypes when you only expected 2 AND explain the number of each phenotype (autosomal linkage)


  - genes are linked

  crossing over has occurred during meiosis to make a new combination of gametes

  - crossing over is rare so not many new gametes are formed
• how to answer questions about autosmoal linkage and crossing over

  - compare the phenotypic ratio to the numbers on the table

  - if the values are consistent with the ratios then crossing over has NOT occurred so the genes are linked by autosomal linkage

  -if the values are NOT consistent with the ratios crossing over HAS occurred genes are not linked by autosomal linkage
• If genes A and B occur on separate chromosomes they are...

  not linked
• If genes A and B occur on the same chromosome they are...

  linked
• If you have chromosomes each with AA, aa, BB, and bb genes present, that are the possible allele combinations for gametes?

  AB, Ab, aB, ab
• What is epistasis?


  The interaction of genes that are not alleles, in particular the suppression of the effect of one such gene by another.
• How does autosomal linkage play a part in dihybrid crosses having expected phenotype ratios that don't match the observed ratio?

  2 genes must be linked, and so they're on the same chromosome
• What is an example of epistasis in mouse fur colour?

  The expression of a gene for producing black bands for a mouse's fur is affected by the expression of the melanin producing gene. In the absence of melanin, the black band gene, A, cannot be expressed
• What is the chi-squared test?


  Used to test null hypothesis, and tests whether there is significant deviation between the observed and expected values.
• What criteria need to be met in order to use chi-squared?

  - Sample size must be relatively large, over 20

  - Data must fall into discrete categories

  - Only raw counts, not %s

  - Used to compare experimental results with theoretical, like with genetic crosses
• What is the formula for chi squared?

  sum of (observed-expected)^2/expected
• how do u check for a significant value

  calcualted value needs to b grater than critical value

  - less than 5% that differences are due to chance

  reject null hypothesis
• how do u write an null hpothesis

  there will be no significant differnecre between observed and expected value
• types of phenotypic variation

  -genetic and environmental
• source of genetic variation

  mutations

  meosis

  random fusion of gametes
• how does selection pressure work

  - prediation, disease and competion result in selection prssures

  - some organisms with certain phenotypes have selctive advantage

  -more likely to survive and reproduce and pass on favourablle alleles to the next generation this is due to change in allele frequency
• What is a gene pool?


  All of the alleles in a population
• What is allele frequency?


  How often an allele occurs in a population