10.2 - Inheretance

Question 1

what is the locus of a gene?

Answer 1

• the specific position it is found on one chromosome type
• In general, chromosomes will have the loci for a group of genes, these are called linkage groups
• When two chromosomes have the same sequence of genes, they are called homologous
• Homologous chromosomes not usually identical as there are some differences in alleles to at least some of the genes

Question 2

linked genes and Mendel’s law.

Answer 2

• Mendel’s law of independent assortment does not apply to linked genes because linked genes are often found on the same chromosome and will therefore be inherited together
• linked genes do not follow expected Mendelian ratios of 3:1 (monohybrid traits) or 9:3:3:1 (dihybrid traits)
• Recombination by crossing over can decouple these linkage groups though

Question 3

how do you present dihybrid cross?

Answer 3

• unlinked genes, alleles are shown side by side e.g. AaBb
• crosses involving gene linkage, the accepted annotation is to show them as vertical pairs (on top of each other)

Question 4

how to identify recombinants.

Answer 4

• Recombinants in linked genes are those offspring that possess entirely different combinations of alleles from either of their parents
• from crossing over
• chromosome or DNA with a new combination of alleles is called recombination
• person with recombinant chromosome has a different combination of characters from either parent and is called a recombinant

Question 5

what is segregation?

Answer 5

• occurs during meiosis and is the separation of the two alleles of every gene

Question 6

how does Independent assortment occor?

Answer 6

• occurs in unlinked genes (genes on separate chromosomes) as the alleles of one gene segregate independently of the alleles of other genes
• Genes found on different chromosomes are unlinked and will assort independently during meiosis
• Therefore genes that are linked tend to be ones on the same chromosome and so these genes do not segregate independently
• exception when genes are far away and unlinked bc of crossing over.

Question 7

what are the exceptions to Mendel’s rules?

Answer 7

• the environment had greater
  influences on the organisms’ variation
• reinforced aspects of Mendel’s studies of independent assortment, and identifying the role of sex-linkage
  of genes

Question 8

what is a Dihybrid trait Punnett square used for?

Answer 8

• investigates the inheritance of two genes together
• can be used to predict the probability of a particular genotype as well as the probability of a particular phenotype

Question 9

what did Mendel find with dihybrid cross of pure breed peas?

Answer 9

• All the F1 hybrids had round yellow seeds, this was not surprising as these characteristics were dominant.
• When Mendel allowed the F1 plants to self-pollinate, he found four different phenotypes in F2 generation: round yellow, round green, shrivelled yellow and shrivelled green.
• Given that F1 hybrids were heterozygous, there were four possible gametes.
• If the inheritance of these two genes is independent, then the chance of a gamete containing R or r will not be affected by the chance of either Y or y.
• The chance of a gamete containing each allele is ½, and so combining two alleles, it would be ½ x ½ = ¼.
• This theory that the two alleles are passed without influencing one another is called independent assortment.

Question 10

what is variation?

Answer 10

• the differences between individual organisms of the same species
• can be discrete (or distinct categories) or continuous

Question 11

what is discrete variation?

Answer 11

• when individuals fall into many distinct categories
• controlled by alleles of a single gene or a small number of genes with the environment having very little effect on its expression
• eg. human blood types: O, A, B and AB

Question 12

what is continuous variation?

Answer 12

• combined effect of many different genes and this is known as polygenic inheritance
• often affected by environmental factors
• polygenic variations tend to form continuous variations of a characteristic
• eg. skin pigmentation in humans

Question 13

how does environmental influence work?

Answer 13

• the differences in phenotype between the classes are subtle and the effects of the environment can blur these differences so much that
  they are undetectable
• Human height and skin colour are both examples of continuous variation. Both are affected by differences in the environment.

Question 14

hypothesis in chi-tests.

Answer 14

• The null hypothesis (H0): the traits assort independently (not linked).
• The alternate hypothesis (H1): the traits do not assort independently (linked)

Question 15

what is the expected ration for dihybrid crosses?

Answer 15

-The ratio of expected phenotype frequencies in a dihybrid cross is 9:3:3:1 for F2 phenotypes following F1 crosses.

Question 16

know how to calculate chi-squared test.