From whom do we inherit our characteristics from, and what are the chances of it being from either of our parents? In this IBDP Biology blog, we will learn the inheritance of our genetic code, as well as how genes can be transfered from one usage to another.
Recap of definitions
DNA: genetic blueprint which codes for the characteristics of an organism
Genes: a sequence of DNA that encodes for a specific trait
Alleles: alternative forms of a gene that code for the different variations of a specific trait
Genome: totality of genetic information of a cell, organism or organelle
Inheritence: Inheritence decides what alleles we get, and so what proteins we are able to make and so which physical characteristics we have
Co-dominance: Multiple alleles for a characteristic that are dominant. Both alleles are expressed
Inheritance
- Gametes are haploid [one copy of each chromosome] contain one allele of each gene
- Each parent has one gamete
- Resultant diploid cell from fertilization is called the Zygote
- Zyote will have two alleles of each gene from each parent
- Genes can have two alleles: One is dominant the other one is recessive
- This produces three possible genotypes:
- AA
Homozygous Dominant (dominant phenotype)
- Aa
Heterozygous (dominant phenotype)
- aa
Homozygous Recessive (recessive phenotype)
Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects
Example of co-dominance: Blood Type
ABO blood typing: example of multiple alleles and co-dominance:
- Antigens are present in type
A, B and AB
- No Antigens (absent) from
type O
i - no antigens present (O)
IA - type A antigens present
IB - type B antigens present
AA: and AB:
Homoygous IA Heteroygous A and B
Phenotype is Type A antigens Phenotype is Type A and B antigens
Blood Compatibility Type A or Type O Blood Compatibility Universal Recipient
BB: and ii:
Homozygous IB Homozygous i
Phenotype Type B antigens Phenotype: Type O (no antigens)
Blood Compatibility Type B or Type O Blood Compatibility Univeral Donor
Ai and Bi:
Heterozygous IA and i Heterozgous IB and i
Phenotype: Type A antigens Phenotype: Type B antigens
Blood Compatibility: Type A or Type O blood Blood Compatibility: Type B or Type O
Autosomal Genetic Diseases
Autosomal gene: Gene wholes loci is on an autosome not a sex chromosome
Genetic disease: Disorder caused by a gene
Autosomal Genetic Diseases: Disease caused by recessive alleles and the locus of their genes is found on one of the first 22 pairs of chromosomes
Example: Cystic fibrosis
- Most disease-causing alleles are
recessive - individual must inherit both copies of the disease allele to actually have the disorder. Indiviuals can be carriers for genetic disorders
- Carriers: 'carry' one copy of the recessive disease allele and one dominant allele that gives them a normal phenotype
Sex-linked Diseases
In IBDP Biology, we need to know what sex-linked genetic diseases are.
Sex-linked Genetic Diseases: Diseases where the gene is carried on the sex chromosome [X or Y]
Red-green colour blindness and hemophilia as examples of sex-linked inheritence
- Females [X X] produce only eggs containing the
X chromosome [2 copies of each gene]
- Males [X Y] produce sperm which can contain either
X or Y chromosomes [1 copy of each gene]
- X and Y chromosomes are
non-homologous chromosomes. Few genes of Y chromosome, X chromosome is large with important genes on it
- Only females can be carriers
of these diseases while males inherit conditions due to alleles more frequently shown
Colour-blindness
- Human females can be homozygous or heterozygous with respect to
- sex-linked genes
- Heterozygous females are carriers
Hemophilia
- Blood clotting requires globular proteins called clotting factors
- Recessive x-linked mutation
- in hemophiliacs results in globular proteins or clotting factors
- not
- being produced
- Hemophiliac is injured blood does not clot and patient can bleed to death
And we're done with the topic of inheritance and sex-linked genetic disorders!
References:
https://www.google.com/url?sa=i&url=http%3A%2F%2Fapenderforensics.blogspot.com%2F2009%2F09%2Fblood-type-charts.html&psig=AOvVaw0EdHhv0BPoAz7BWcmvryN0&ust=1624964534145000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCNjW1-GWuvECFQAAAAAdAAAAABAY
https://www.google.com/search?q=autosomal+disease+cystic+fibrosis&tbm=isch&ved=2ahUKEwiN19aqmLrxAhXJBKYKHYVLA1IQ2-cCegQIABAA&oq=autosomal+disease+cystic+fibrosis&gs_lcp=CgNpbWcQA1DdVFiEaWCTamgBcAB4AIABwAGIAecJkgEDNC42mAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=363ZYM3rFsmJmAWFl42QBQ&bih=765&biw=1440&rlz=1C5CHFA_enHK733HK733#imgrc=nB-j3vd7NmH_2M
https://www.icegif.com/wp-content/uploads/boxing-day-icegif-6.gif
Written by Venetia (Biology)