Patterns of Inheritance

Question 1

Environmental example

Answer 1

• diet in animals
• etiolation in plants= elongation of internodes of plants to reach the sunlight
• chlorosis in plants= plant does not produce chlorophyll after being kept in dim light so are yellow/white

Question 2

Continuous variation

Answer 2

-when the individuals in a population vary within a range - there are no distinct categories,

• usually polygenetic. The greater number of gene loci contributing to the determination of the characteristic,the more continuous variation

Question 3

Discontinuous variation

Answer 3

-when there are two or more distinct categories - each individual falls into only one of these categories, there are no intermediates

-usually monogenetic

Question 4

Sexual reproduction has lead to genetic variation

Answer 4

• crossing over in propase 1
  -independent assortment of chromosomes during metaphase/anaphase 1 + 2
• random fusion of gametes

Question 5

Monogenetic inheritance

Answer 5

• inheritance of one single gene
• homozygous dominant, homozygous recessive
  3:1 expected ratio

Question 6

Dihybrid inheritance

Answer 6

-inheritance of two different genes= 4 alleles
- parent genes crosses are homozygous dominant and homozygous recessive.

• ratio= 9:3:3:1

Question 7

What to always include in a crossing over questions

Answer 7

The genotype of the parents you are crossing,
2. The gametes from the parents (in circles)
3. The actual cross (punnet square)
4. A ratio of the offspring’s genotype or phenotype (depending upon the Q1.

Question 8

Multiple sex

Answer 8

-more than two alleles of the same of the same gene

Question 9

Codominances

Answer 9

• both alleles are expressed in the phenotype e.g. sickle-cell anaemia

Expected ratio 1:2:1

Question 10

Sex-linkage

Answer 10

• Sex-linked genes are located on a sex chromosome, and X-linked genes are located on the X chromosome.

Question 11

Epistasis

Answer 11

• When a gene suppresses another gene, the gene doing the suppressing is called the epistatic gene
  -can be recessive or dominant
  -recessive expected ratio= 9:3:4 with a homozygous recessive and homozygous dominant
• expected ratio of dominant homozygous of the same thing= 12:3:1

Question 12

Autosomal linkage

Answer 12

This occurs on the autosomes (any chromosome that isn’t a sex chromosome) Two or more genes on the same chromosome do not assort independently during meiosis. These genes are linked and they stay together in the original parental combination.

• reduces genetic variation of crossing over doesn’t occur

Question 13

Why might you not get the expected phenotypic ratio

Answer 13

-random fertilisation
-autosomal linkage + no crossing over occurred to separate the genes.

Question 14

Chi-squared test

Answer 14

X2= sum of (O-E) squared divided by E
O= observed
E= expected results
Degrees of freedom= n-1 at a 5%(0.05) level

• null hypothesis= no difference between observed and expected
• to work out expected value from phenotypic ratios= total sample number/ total ratio number x n.o. In ratio the sample represents( CGP)
• higher than critical value= less than 5% certain results not due to chance = statistically significant
• lower than critical= 95% certain results due to chance= not statistically different

Question 15

Stabilising selection

Answer 15

-environment isn’t changing much
- individuals with alleles for characterisations forward the middle of the range are more likely to survive and reproduce

Question 16

Directional selection

Answer 16

• changes in the environment where the alleles for characteristics of extreme types are more likely to survive and reproduce

Question 17

Genetic drift

Answer 17

• change in allele frequencies in a population from generation to generation that occurs due to chance events
  -e.g. one allele selected by chance more than other- has a larger effect in smaller population.
• in larger populations allele frequency tends to even out

Question 18

Genetic bottle neck

Answer 18

• event such a natural disaster causes a big reduction in a population size leading to a reduction in the gene pool

Question 19

Founded effects

Answer 19

• when individuals from a larger population are isolated and created a new population resulting in loss of genetic variation
• may be due to migration, or religious isolation e.g. the Amish

Question 20

Hardy-Weinberg principle

Answer 20

• p= the frequency of dominant allele
  -q=the frequency of the recessive allele
  -p2= homozygous dominant genotype
  -q2=homozygous recessive
  -2pq= the frequency of the heterozygous genotype
• P IS BEFORE Q

Question 21

Allopatric speciation

Answer 21

• a result of geographic isolation
• physical barrier divides a population of species, conditions on either side of the barrier will be slightly different therefore different characteristics will be more common and advantageous so allele frequency will change until two species are not getting

Question 22

Speciation

Answer 22

The development of a new species

Question 23

Sympatric speciation

Answer 23

-a result of reproductive isolation which is a change in the allele and phenotypes of the two populations which prevent them from successfully breeding together

-seasonal changes= individuals from the same population may become sexually active at different times
- mechanical changes= changes in genitalia preventing successful mating
- behavioural changes= a group of individuals develop courtship rituals that aren’t attractive to the main population

Question 24

Artificial selection

Answer 24

Artificial selection is the process by which humans choose organisms with desirable traits and selectively breed them together to enhance the expression of these desirable traits over time and over many generations
This practice is also known as selective breeding. (Two individuals with the desired characteristics are bred together)

Reasons for selective breeding:
-Disease resistance in food crops
Increased yield
Hardiness to weather conditions (eg. drought tolerance)
Better tasting fruits
Large or unusual flowers

Question 25

Ethical considerations of artificial selection

Answer 25

• reduction in the gene pool can lead to harmful health effects due to inrbreeding
  -Organisms being vulnerable to new diseases
  -traits in dogs may put them at a disadvantage in the wild
• desirable colour of humans may fail to camouflage the animal
  -have caused breathing problems in pedigree dogs such as pugs
• it’s not fair to cause health problems on dogs