Ch 5. Principles of Inheritance and Variations (Stack 3) Flashcards
Explain sex determination in humans
It has already been mentioned that the sex-determining mechanism in the case of humans is XY type. Out of 23 pairs of chromosomes present, 22 pairs are exactly the same in both males and females; these are the autosomes.
A pair of X-chromosomes are present in the female, whereas the presence of an X and Y chromosome are determinants of the male characteristic.
During spermatogenesis among males, two types of gametes are produced . 50 percent of the total sperm produced carry the X-chromosome and the rest 50 percent has Y-chromosome besides the autosomes. Females, however, produce only one type of ovum with an X-chromosome. There is an equal probability of fertilization of the ovum with the sperm carrying either X or Y chromosome. In case the ovum fertilizes with a sperm carrying X-chromosome the zygote develops into a female (XX) and the fertilization of ovum with Y-chromosome carrying sperm results in a male offspring
Explain sex determination in Drosophila melanogaster.
Mechanism of sex detem1ination in Drosophila melanogaster is XY type where both male and female have a same number of chromosomes. Among the males an X-chromosome is present but its counterpart is distinctly smaller and called the Y-chromosome.
Females, however, have a pair of X-chromosomes. Both males and females bear a same number of autosomes. Hence, the males have autosomes plus XY, while females have autosomes plus XX. In Drosophila the males have one X and one Y chromosome, whereas females have a pair of X-chromosomes besides autosomes.
Explain sex determination in birds
In this case of Birds, the total number of chromosomes is the same in both males and females. But two different types of gametes in terms of the sex chromosomes, are produced by females, i.e., female heterogamety.
ln order to have a distinction with the mechanism of sex detemination described earlier, the two different sex chromosomes of a female bird have been designated to be the Z and W chromosomes. In these organisms, the females have one Z and one W chromosome, whereas males have a pair of Z-chromosomes besides the autosomes.
Explain sex determination mechanism in grasshopper
Grasshopper is an example of XO type of sex determination. Where all eggs bear an additional X-chromosome besides the other chromosomes (autosomes). On the other hand, some of the sperms bear the X-chromosome whereas some do not.
Eggs fertilised by sperm having an X-Chromosome become females and, those fertilised by sperm that do not have an X-chromosome become males. In Grasshopper the males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes
Explain sex determination mechanism in honey bees
The sex determination in honey bees is based on the number of sets of chromosomes an individual receives. An offspring formed from the union of a sperm and an egg develops as a female (queen or worker), and an unfertilised egg develops as a male (drone) by means of parthenogenesis.
This means that the males have half the number of chromosomes than that of a female. The females are diploid having 32chromosomes and males are haploid, i.e. , having 16 chromosomes. This is called a haplodiploid sex-determination system and has special characteristic features such as the males produce sperms by mitosis
Define muation.
Any alteration in the DNA sequence which can be inherited and may be expressed as a change in the phenotype of an organism is called a mutation.
What is deletion mutation
A gene mutation which involves deletion of one or more base pairs of DNA has deleted.
What is insertion mutation?
A gene mutation involves the addition of one or more base pairs in DNA.
What is point mutation?
A gene mutation which involves change in a single base pair of a DNA is called point mutation
Mention an example for point mutation
Sickle cell anaemia
What is frame shift mutation?
Insertions and deletion of a base pair or base pairs in a DNA are referred as frame shift mutations.
What are mutagens?
Mutation causing agents called as mutagens
What is pedigree analysis?
Analysis of traits in a several of generations of a family is called the pedigree analysis
Write the representative pedigree analysis (pedigree chart) of myotonic dystrophy as an example for autosomal dominant trait.
Write the representative pedigree analysis (pedigree chart) of sickle cell anemia as an example for the autosomal recessive trait
What is thalassemia?
Thalassemia is an autosomal recessive blood disorder in which the body makes an abnormal form of hemoglobin due to a mutation in the genes coding for its alpha or beta chain.
What are Mendelian disorders
The disorders which arise by alteration or mutation in a single gene are called Mendelian Disorders.
eg : Haemophilia, Cystic fibrosis.
Mention an example for a mendelian disorder
Haemophilia.
Give an example of sex-linked recessive disease in humans
Haemophilia
Name an autosomal recessive Mende lia n disorder in humans
Sickle-cell anaemia.
Mention an example of an inborn error of metabolism caused due to a recessive allele on the autosome
Phenylketonuria
Name the enzyme that is not produced due to gene mutation which causes phenylketonuria
phenylalanine hydroxylase.
Phenyl pyruvic acid and its derivatives are excreted through urine in phenylketonuria. Why?
Phenylketonuria is due to a deficiency of phenylalanine hydroxylase enzyme, which converts phenylalanine into tyrosine.
As a result, phenylalanine accumulates in the circulation which is converted to phenylpyruvate and is excreted in the urine because of its poor absorption by the kidney.
Why persons with phenylketonuria normally suffer from mental retardation
Persons with PKU suffer from mental retardation as accumulation of phenylalanine and its derivatives in the blood causes brain damage, seizures, etc.
What is haemophilia?
Haemophilia is sex linked recessive disease in which a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected.
Why the possibility of a female becoming a haemophilic is extremely rare?
The possibility of a female becoming a haemophilic is extremely rare because the mother of such a female has to be at least carrier and the father should be haemophilic (unviable in the later stage of life).
In a haemophilic patient, why even a simple cut results in non-stop bleeding?
In an affected individual a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, a simple cut will result in non-stop bleeding.
What is colour blindness
It is a sex-linked recessive disorder due to defect in either red or green cone of the eye resulting in failure to discriminate between red and green colour.
What is sickle cell anaemia?
Sickle cell anaemia is an autosome-linked recessive where a mutant haemoglobin molecule undergoes polymerisation under low oxygen tension causing the change in the shape of the RBC from biconcave disc to elongated sickle like structure
RBCs become sickle-shaped in persons suffering from sickle cell anaemia. Why?
RBCs become sickle-shaped in persons suffering from sickle cell anemia, because mutant haemoglobin molecule undergoes polymerization under low oxygen tension causing the change in the shape of the RBC.
Name the amino acid which substitutes glutamic acid in the beta globin chain of haemoglobin in sickle cell anaemia
Valine
Name the amino acid in the beta-globin chain of haemoglobin that is substituted by valine in sickle cell anaemia
Glutamic acid
Mention the sixth codon of beta globin chain in normal haemoglobin
GAG
. Write the sixth codon of beta-globin chain in haemoglobin of sickle celled anaemic patients
GUG
Which genetic disease is characterized by the reduced synthesis of haemoglobin?
Thalassemia
