Inherited Change

Question 1

Define genotype

Answer 1

The genetic constitution of an organism/the alleles expressed in an organism

Question 2

Define phenotype

Answer 2

The observable or biochemical characteristics of an organism/ the expression of gene constitution and its interaction with the environment

Question 3

Define dominant, recessive and co dominant alleles

Answer 3

The allele of the heterozygous pair that expresses itself in the phenotype is dominant and the one not expressed is recessive. Co dominance is when both alleles occur together and the phenotype is a blend (roan) or both are represented (AB blood group)

Question 4

Define multiple alleles

Answer 4

When there are more than 2 alleles for a gene (onto 2 can be represented as 2 chromies in a pair)

Question 5

Describe how to draw a punnet square / genetic diagram and draw it out

Answer 5

First make a table with parent phenotype, genotype and then gamete genotype. Draw punnet to sausage with game genotypes. Make sure to include the phenotype underneath

Question 6

Explain how a single gene is inherited

Answer 6

Pea plants with green pods were bred repeatedly so they consistently produces plants with green pods, meaning they were pure bred (means homozygous). Means in diploid, characteristics are determined by alleles that occur in pairs but only one of each pair is present in a single gamete

Question 7

Rule for hetero with hetero and hetero with recessive

Answer 7

Het and het- 3:1, het and recessive- 1:1

Question 8

Why do results from genetic crosses differ from expected results

Answer 8

Random fusion of gametes (fertilisation) is a chance event but the larger the sample size, the close they will be to expected ratio

Question 9

Explain dihybrid inheritance

Answer 9

The inheritance of 2 characteristics determined by 2 different genes on different chromosomes at the same time. 2 pairs of gametes can be made with combinations of both characteristics. (Use set menu analogy each gamete must have a main and a dessert) Can use cancelling if gametes the same to use smaller punnet. Het x het- 9:3:3:1 het x homo recessive- 1:1:1:1

Question 10

What notation is used for codominace

Answer 10

Superscript (when the feature is like something squared)

Question 11

Describe blood group inheritance in humans

Answer 11

3 alleles associated. Allele I to the A, leads to the production of antigen A, allele I to the B, produces antigen B and allele I to the O, does not lead to either antigen production. A and B are codominant and O is recessive

Question 12

Describe the basics of meiosis

Answer 12

Produces haploid gametes which fuse to produce a diploid zygote. 1.before division (a diploid pair of homologous chromosomes) 2. Interphase (homologous pair of replicated chromosomes). 2. Meiosis 1 (undergo cell division where homologous pair separates in prophase 1, crossing over occurs which is formation of chiasmata between chromatids and in meta/ana phase 1, independent segregation occurs. Both increase variation). 4. Meiosis 2 where sister chromatids separate (haploid). After random fertilisation occurs= increases variation

Question 13

How to work out the possible combinations made from independent segregation then from independent segregation and random fertilisation

Answer 13

Independent segregation- 2 to the n where n is no. Pairs of homologous chromosomes. Independent segregation and random fertilisation- (2 to the n) squared

Question 14

How is sex determined genetically

Answer 14

Females have XX sex chromosomes, males have XY sex chromosomes so gametes made are X or X for females and X or Y for males. Punnet square Shows 50/50 chance of make or female and sex determined by male as they carry the Y chromosome needed for males

Question 15

What is meant by sex linkage

Answer 15

Any gene that is carried on the X or Y chromosome is sex linked ( X longer than Y so for most of X length, there’s no equivalent portion on Y= characteristics controlled by recessive alleles on X occur more frequently in males as no length on Y that could be dominant)

Question 16

Is wild type dominant or recessive and what is reciprocal cross

Answer 16

Wild type is dominant and reciprocal cross is when you flip genetic cross other way around and get same results is sex linked

Question 17

Explain how sex linked diseases such as haemophilia are inherited (draw out diff combos)

Answer 17

Haemophilia is a blood clotting disorder , caused by recessive allele for dysfunctional protein on X chromosome (X to the h). As males only obtain Y from father, X and the disease is inherited from the mother. Carrier female x normal male = 2:1:1 Normal female:carrier female:haemophiliac male . Normal female x haemophiliac male= 1.1 carrier female:normal female as males pass allele to daughter on X chromosome

Question 18

Explain the concepts of pedigree charts

Answer 18

Used to trace inheritance of sex linked characteristics. Males are squares, females circles and shading indicated the presence of a characteristic

Question 19

What is the evidence that an allele is recessive in a pedigree chart

Answer 19

Unaffected parents have affected children

Question 20

Evidence from pedigree chart that an allele is not on an X chromosome

Answer 20

Unaffected father produces affected daughter

Question 21

Evidence that a disorder is sex linked

Answer 21

Only seen in males

Question 22

How do carry out a chi squared test

Answer 22

1. find expected data using a punnet square to find the expected ratio. Add up the ratio and divide the total of observed data by the total ratio to find :1 then times up to find the expected results. 2. 0-E 3. O-E squared 4. O-E squared divided by E. 5. Add up last column to give the chi squared value. 6. Find the degrees of freedom (no. Categories minus 1) in the 0.05 column to find critical. If calculated value is less than critical ACCEPT null:no sig diff between O and E any diff due to chance (more than 5% prob diffs due to chance)

Question 23

Explain what the chi squared test is

Answer 23

A statistical analysis used to evaluate whether the differences between observed and expected data are statistically significant

Question 24

What is epistasis

Answer 24

When 2 genes (on diff chromosomes) interact together to affect phenotypes. The allele old one gene may affect/mask the expression of another

Question 25

Define autosomal linkage/ linkage

Answer 25

Two or more genes located on the same chromosome, independent assortment of alleles does not occur/ any two genes that occur on the same chromosomes are linked

Question 26

Define crossing over

Answer 26

The reciprocal exchange of DNA between non sister chromatids

Question 27

The expected ratio, notation and explanation of linked genes

Answer 27

3:1 of no crossing over, have to write letters linked by a line and only one pair of homologous chromosomes needed for 4 alleles to be present

Question 28

Suggest a reason why the number of things in each category of crosses aren’t the same

Answer 28

Random fertilisation of gametes is a chance event

Question 29

How would a plant breeder ensure offspring produced from a plant are only from the desired cross

Answer 29

Remove anthers, transfer pollen by hand, isolate plants, bag flowers before and after pollination and could use male sterilisation via hormones

Question 30

How to calculated a percentage cross value

Answer 30

Number of recombinant offspring over total number of offspring x 100

Question 31

Describe recombination/ crossing over on linked genes

Answer 31

If a different distribution for 2/4 categories: recombination has taken place. 2 genes on sister chromatids swapped round which gave new combinations. The further apart 2 linked genes are, the greater % of recombination. Demo on small pack question 4 C iii