Inheritance Exam Questions Flashcards
(a) Cystic fibrosis is caused by a recessive allele. Explain the evidence for this given in the diagram.
(b) Couple 7 and 8 decide to have another child. What is the probability that this child will be a girl with cystic fibrosis? Complete the genetic diagram to explain your answer. Use the symbols N for the dominant allele and n for the recessive allele.
a) ev.
- parents 1 and 2 are unaffected but have an affected child.
- If the trait is recessive neither parent is required to have the trait since they can be heterozygous.
- 6 has inherited one recessive allele from each parent.
- if the alleles were codominant, sandy would be a combination of red and white alleles (C^R and C^W).
- 7 and 8 are red so they should have the genotypes C^RC^R and C^RC^R and produce all red offspring.
- it shouldn’t be possible for them to have sandy offspring.
Also if the alleles were codominant, all the offspring of 3 and 4 would all be sandy.
(Evident from punnet square of possible offspring).
10 and 11 - all offspring should be sandy.
11: aabb
-as from the pedigree diagram, 11 is white. Hypothesis 1 states that an individual with a white phenotype has the the genotype aabb.
10: AaBb
- from the pedigree diagram, 10 is red. Hypothesis 1 states that an individual with a white phenotype has the the genotype A_B_.
- Since the _ represents a dominant or recessive allele, you can fill this in.
How do you know the second allele of each gene are not dominant?
2: A_bb OR aaB_
- from the pedigree diagram, 2 is sandy. Hypothesis 1 states that an individual with a sandy phenotype has the the genotype A_bb OR aaB_.
Explain one piece of evidence from the diagram which shows that hypothesis 2 should be rejected.
Explain why hypothesis two could not account for the observed result.
e.g. if sandy was aaB_, individuals 1 and 2 would both have been aaB; so their offspring could only be either white or sandy (as no A alleles are present).
Individual 18 was crossed with a pig with a genotype Aabb.
Use hypothesis 1 to predict the genotypes and the ratio of phenotypes expected in the offspring of this cross.
In a breed of cattle the H allele for the hornless condition is dominant to the h allele for the horned condition. In the same breed of cattle the two alleles C^R (red) and C^W(white) control coat colour. When red cattle were crossed with white cattle all the offspring were roan. Roan cattle have a mixture of red and white hairs.
a) name the relationship between the two alleles that control coat colour.
b) Horned, roan cattle were crossed with white cattle heterozygous for the hornless condition. Complete the genetic diagram to show the ratio of offspring phenotypes you would expect.
The semen of prize diary bulls may be collected for vitro fertilisation. The sperms in the semen can be separated so that all the calves produce dare of the same sex. Two kinds of sperms differ by about 3% in DNA content.
(i) Explain what causes the sperms of one kind to have 3% more DNA than sperms of the other kind.
(ii) Suggest why farmers would want the calves to be all the same sex.
(i) X is larger; has more genes than Y.
(ii) females for milk/ males for meat/ males and females for breeding
(a) What is the diploid number of chromosomes in the organism from which this cell was taken?
b) Describe what is happening to the chromosomes at the shown in :
(i) Fig 1
(ii) Fig 2
a) 6
b)
Fig. 1) Chromosomes are arranged in homologous pairs
/crossing over
/exchange of genetic information; bivalents arranged independently.
Fig. 2)
- separation/ pulling apart of homologous pairs chromosomes
- pulled at centromere by spindle fibres.
(i) The genotype of this organism is Bb. The locus of this pair of alleles is shown in Fig. 1.
Label two chromosomes on Fig.2 to show the location of the B allele and location of the b allele.
(ii) How many genetically different gametes can be produced by meiosis from a cell with the genotype Bb Cc Dd? Assume these genes are located on different pairs of homologous chromosomes. Show your working.
Answer Qs (b) and (c)
