GENETICS

8

Monohybridinheritance

1a: A punnet table indicating heterozygous man and woman for freckles.

Answer:All their children will have freckles.

(2marks)

f

F

f

F

Ff

Ff

Offsprings

Ff

Ff

&nbsp

&nbsp

1b: A punnet table for homozygous woman with short fingers that aredominant and a man whose short fingers are heterozygous.

S

S

s

s

Ss

Ss

Offsprings

Ss

Ss

Answer:One of their children will have long fingers and one short fingers.

(2marks)

Probability= 1:1, which is 1/2

1cOne of their grandchild has a potential for longer fingers. Thechild with predominant long fingers when married or marries one withpredominant long finger one of their child will have longer fingersas illustrated in the following table:

s

S

s

S

Ss

SS

Grandchildren

SS

Ss

3Dihybrid Inheritance

3a.Floppy ears: EE

Pointyears: Ee

Bowlegsthat recessive: ll

(1mark).

3b.

Heterozygousgoat with floppy ears legs that are bowed: Ee ll

Agoat with heterozygous traits in the both the ears and bowlegs: Ee lL

3c.Phenotypes resulting from the parents mating using Punnet table. (3 marks).

Traits

Heterozygous ears

Recessive legs

Heterozygous ears

Heterozygous legs

Ee,ll

Ee

Ll

Ee

LI

1st Generation

EE

ee

IL

II

2nd Generation

Ee

Ee

II

LI

3rd Generation

EE

ee

IL

II

4. The process that leads to production of diploid and haploid cells

DuringMeiosis division of successive nuclear, two processes in occurs. Theprocess is divided in two. commonly knowns as Reduction or Meiosis Iand the Division phase known as Meiosis II. Both of the processeshappen separately leading to production of diploid and finallyhaploid cells. The entire process of meiosis result to production offour cells that are haploid. There is reduction of nuclear to n from2n. Meiosis II separates the rest chromosomal set in a divisionprocess. Major differences in the process occur during Meiosis I.The process comprises of various phases that consist of prophase I,which is where crossing over takes place, and break down ofchromatids. They can be later attached to varied homologouschromosomes. It leads to four chromosomal production. DuringMetaphase I, the spindly is lined with tetrads. The tetrads separatein Anaphase I while the centromeres remaining are tied together. Itoccurs in the centre. In the Telophase, there is a chromosomalnucleus gathering leading to division of the original cell. ProphaseII lead to nuclear desorption. In Metaphase II there is movement tothe equatorial area by the chromosomes. In Anaphase II there is asplit to form chromatids. Finally, in Telophase II, there isseparation of cytokinesis cells. New cell are formed that resemblethe initial one and the process is recurrent (Kindfield , 2004).

5.Sex Linkage

  1. Chromosome x for color, allele red being the dominant over white. Work on possible offspring (2 marks)

White eyed female

(x)

x

Red eyed male

(X)

Gametes

Xx

XX

Offspring

Xx

Xx

b)Advantages of sexual reproduction and alternative reproduction methodused by a specific organism. .

Sexualreproduction allows exchange of genes between two individuals ofdifferent genetic makeup. The exchange of genes provide theopportunity for organism with good genetic traits to exchange withanother one with poor genetic traits hence provide a chance ofreproducing an hybrid offspring. The advantage of sexual reproductionis that the offspring are of hybrid compared to their parent. Thepoor traits of the parent are eliminated through the geneticexchange. In the case where one parent is white the other red colour,the parent are most likely to reproduce offspring who have red colourthough they will still be carrying dormant traits of white colour.The offspring, which can adapt better to the environment, will alsobe produce.

Thealternative reproduction asexual reproduction where the an organismwill create identical or similar copies and no genetic exchange.Organism such as bacteria, virus, Hydras and many other single celluse this form of reproduction. Bacteria use binary fussion whileviruses reproduce through taking control of host cells. There is noexchange of genes meaning the parents traits are transferred directlyto the offspring. The offspring are usually inferior compared to theparents

(4marks)

6.Pedigrees

a.Inheritanceof disorder-This is inherited as dominant. This is because theprobability of getting an offering with disorder and that withoutremains equal. The first off springs were one of good health andanother with disorder.

b.phenotype example and why the children four, five and six did notsuffer from disorder.

I- Parents Xx ( without disorder), xx( with disorder since x wasdominant)

  1. Offspring Xx, xx Xx

  1. Offspring xx, Xx, xx

Iii-Offspring Xx, Xx, Xx, Xx( all ended up as carriers of deforms) suchwas because one parent was XX and other one had xx. If these childrengets their own children, half of them are expected to have deformssince their parents were carriers of the disorder

Theproportion of unaffected children is

P(xx) = 0.04

Xx=0.8

XX=0.16,unaffected children

(5marks)

7.Hardy Weinberg

.Dominant while Black alleles and frequency of the three possibledrives

p2&nbsp+2pq + q2&nbsp=1&nbspalso

p+ q = 1

Frequencyfor black (bb) =0.04 which is 22

Sothe white (BB) is 0.80

Othercolors (Bb) = 0.16

Frequencyof black (bb) =22

Then20% = 22

Thenwhite, BB = 80/100= 720

Frequencyof white (BB) = 720

Frequencyfor other colours = 156

  1. Hitchhiker`s thumb is dominant while straight thumb recessive. Summing up there are 1000 individuals with 510 dominant phenotype, determining each phenotype the calculation is done as follows.

p2&nbsp+2pq + q2&nbsp=1&nbspandalso

p+ q = 1

80%=510

Then20% =20/100x 900 =200 straight thumbs

Then1000-710=290, normal thumps.

2T:1t so it is t=85

ThenTt=740

Reference

Kindfield,A.C., 2004. Understanding a basic biological process: Expert andnovice models of meiosis.&nbspScienceEducation,&nbsp78(3),pp.255-283.