- Rumana Anam
Explain all types of inheritance highlighting the monohybrid and co dominant inheritance in particular.
Inheritance is the genetic traits and characteristics that are passed on from the parent to the next generation of offspring. There are a few types of Inheritance, Dominant-Recessive, Incomplete Dominance, Co Dominant, Sex Limited, Sex Linked and Monohybrid.
Monohybrid – This is when two organisms that only differ at one trait are bred together. This can be very usefully, as the offspring can be determined by looking at the genes of the parent chromosomes and also this process can prove very useful in selective breeding of plants and animals. However the most usefulness of monohybrid crossover is that of organisms with inherited disease, knowing about the alleles can predicted the outcome of the diseases being passed on to the offspring.
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As chromosomes come in pairs, each chromosome pair will have a gene at the same point. At this point the gene can come in different forms, these different forms are called alleles. Both of the chromosomes will have one allele within the pair, if both alleles are the same they are called, homozygous gene, if they are different they are called heterozygous gene. For example H is a allele for height within one chromosome it produces tall offspring and the other allele is h within the chromosome it produces short offspring. Therefore if there is a combination of alleles HH or hh of that gene it would be a homozygous gene, but if the combination is Hh then it would be a heterozygous gene (S-cool the revision website, 2015).
Dominant – This is when one or both gametes are dominant, meaning genes that stop other genes from showing their traits, the dominant traits are inherited by the offspring.
Recessive – When the homozygous, are recessive, meaning genes that do not show the traits even when they are present, the off spring will inherit the recessive trait.
(Stand back! I am going to try Science, 2009)
Incomplete Dominance – This is when no one of the alleles has dominance over the other alleles. The offspring would result in a mix between the two homozygous of the parent phenotype, this is a feature that is resulted by the genes and their interaction to the environment, therefore the result would be of heterozygote a pair of two alleles that are different for example if a blue and yellow flower breed, it would result in a green flower.
Co Dominant – This when both alleles within the heterozygote organism show their trait equally by phenotype, for example in some chickens black feather are co dominant with white features resulting in a black and white feathered chicken.
Sex Linked – This when the sex of the offspring is determined. Both males and females have 46 chromosomes, of which 44 are homologous they are the same called autosomes, 2 chromosome are sex chromosomes. A female has 2 chromosomes that are homologous they are the same XX and a male has 2 chromosomes that are different XY. The X chromosome acts as an recessive alleles so when there is a Y chromosome it is dominant.
(Slide share net, 2015)
Describe the inheritance of ABO blood groups, specifying the role of multiple alleles.
Multiple alleles are three or more alleles of the gene within the gene pool with the same traits. However a human can only have two alleles one from each parent. The blood type of a human has three alleles A, B and O of which only two can be inherited. The alleles A and B are co-dominant and the allele O is recessive. If the blood type of a human is A, then alleles AA, or AO has been inherited. If the blood type is B, then alleles BB or BO is inherited. If the blood type is AB, then the alleles A and B have both been inherited as they are co-dominant. If the blood type is O, then the alleles OO has been inherited (Biology online, 2011).
The blood group is determined by which antigen’s are present on the surface of the red blood cell. The genetic make up that is inherited by the off springs from the parents determines which antigen is in the red blood cells (Patient, 2013).
A+ (A positive) if you have A and rhesus antigens.
A– (A negative) if you have A antigens but not rhesus antigens.
B+ (B positive) if you have B and rhesus antigens.
B– (B negative) if you have B antigens but not rhesus antigens.
AB+ (AB positive) if you have A, B and rhesus antigens.
AB– (AB negative) if you have A and B antigens but not rhesus antigens.
O+ (O positive) if you have neither A nor B antigens but you have rhesus antigens.
O– (O negative) if you have do not have A, B or rhesus antigens.
Describe the inheritance of sex chromosomes and explain sex linked inheritance with examples.
Sex chromosomes are a pair of genes that determine whether the offspring is a male or female. In a human sex chromosome is one pair of chromosome out of 23 pair, of which 22 pairs of chromosome are autosomes i.e. they have identical genes. If the parents pass on chromosome X from the mother (as females can only pass on X chromosomes) and X chromosome from the father, then a female offspring is produced, however if the parents pass on chromosome Y from the father and X chromosome from the mother, then a male offspring is produced as Y is a dominant gene. It is the father or male that is responsible for passing on either X or Y chromosome and determine the sex of the offspring, as the mother or female only possesses two of the same XX chromosome (Encyclopedia Britannica, 2014).
Sex linked traits are genetics characteristics that are determined by genes which are located within the sex chromosomes. One allele of trait is inherited form each parent as sex linked traits are passed from parents to offspring. Genes that are found in the sex chromosome are called sex-linked genes. Genes that are located in the Y chromosome are Y linked gene, these genes are only inherited in males as males have a XY chromosomes. Genes that are located in X chromosome are X linked gene, these genes can both be inherited by females and males as they both contain one X chromosome. Genes that contain sex linked traits have two alleles when one allele is dominate and the other is recessive, the dominate trait overpowers the recessive trait and is expressed and the recessive trait will be hidden. However in X linked gene recessive traits within a male will be expressed as the male only contains one X chromosome and there is no dominant trait to overpower the recessive trait. For example
(Feisty home, 2000)
Within a female the recessive sex linked trait may be hidden if the second X chromosome contains a normal dominant allele. For example this can be seen in hemophilia a disorder where the blood does not clot, as hemophilia is an X linked recessive trait, this is more often found in males then females. If a mother is a carrier of the trait and the father does not have the trait then the sons will have a 50/50 of inheriting the disease and the daughters have 50/50 chance of being carriers of the disease. If the sons inherit the recessive chromosome then the disease will be expressed. If the daughters inherit the recessive chromosome, then the dominate chromosome will overpower the recessive chromosome.
(Gene Ed, 2012)
Some examples of recessive sex linked disorders are colour blindness, where there is an inability to distinguish between certain colours. Hemophilia, this is where the blood does not clot due to the absence of one or more proteins needed for blood clotting.
Slide Share 2015, Types of Inheritance, [online] available at http://www.slideshare.net/jayreimer/4genetics-types-of-inheritance-by-cj, last accessed 10/04/15
S-Cool the Revision Website 2015, Monohybrid Crosses, [online] available at http://www.s-cool.co.uk/gcse/biology/genetic-crosses/revise-it/monohybrid-crosses, last accessed 10/04/15
Stand Back! I am going to Try Science 2009, Monohybrid Inheritance and Genetic Keys, [online] available at http://standback.pbworks.com/w/page/15686439/monohybrid%20inheritance%20and%20genetic%20key%20terms, Last accessed 10/04/15
Biology Online 2011, Multiple Alleles, [online] available at http://www.biology-online.org/dictionary/Multiple_alleles, last accessed 10/04/15
Bioserv 2015, Multiple Alleles, [online] available at http://bioserv.fiu.edu/~walterm/GenBio2004/new_chap13_inheritance/pics.htm, Last accessed 10/04/15
Mhhe.com 2015, Chromosomal Sex Determination, [online] available at http://www.mhhe.com/cls/psy/ch02/chrom.mhtml, last accessed 10/04/15
Encyclopedia Britannica 2014, Sex Chromosome Genetics, [online] available at http://www.britannica.com/EBchecked/topic/536952/sex-chromosome, Last accessed 10/04/15
Feisty Home 2000, Beginners Guide to Genetics, [online] available at http://feistyhome.phpwebhosting.com/genes.htm, Last accessed 10/04/15
Gene Ed 2012, Hemophilia, [online] available at http://geneed.nlm.nih.gov/topic_subtopic.php?tid=142&sid=148, Last accessed 10/04/15
Patient 2013, Blood Grouping (Typing), [online] available at http://www.patient.co.uk/health/blood-grouping-typing, Last accessed 23/05/15
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