Human karyotype Flashcards
Describe the main steps of mitosis and meiosis and the main differences between the two.
Mitosis is a duplication process that produces two genetically identical daughter cells from one mother cell.
Meiosis is a reduction process that produces four genetically different daughter cells with half the genome of the parent cell.
The main steps of both processes are:
replication,
alignment,
segregation,
cytokinesis.
The main differences are: mitosis has one round of nuclear division,
meiosis has two;
mitosis produces diploid cells
meiosis produces haploid cells;
mitosis maintains genetic stability,
meiosis introduces genetic variation.
What is a karyotype?
complete set of highly condensed chromosomes that can be seen only when cells divide.
A karyotype can reveal the number, shape, and size of chromosomes, as well as any abnormalities or variations in them.
What are the characteristics of a karyotype? And of human karyotype?
The number and shape of chromosomes are characteristic for each species.
In humans, the normal karyotype consists of 46 chromosomes:
22 pairs of autosomes and one pair of sex chromosomes.
The sex chromosomes determine the sex of the individual:
XX for female and XY for male.
The shape of chromosomes can vary depending on the position of the centromere,
which is the region that holds the sister chromatids together.
There are four types of chromosome shapes:
metacentric,
submetacentric,
acrocentric,
telocentric.
Explain maternal inheritance
Maternal inheritance is the transmission of genetic information from the mother to the offspring through the cytoplasm of the egg cell.
This is the case for mitochondrial DNA, which is inherited only from the mother and not from the father.
Mitochondrial DNA is a circular molecule that encodes some genes for the function of the mitochondria, the organelles that produce energy for the cell.
What is chromosome non-disjunction?
failure of homologous chromosomes or sister chromatids to separate during meiosis or mitosis.
results in aneuploidy, which is the variation in the number of chromosomes in a cell or an organism.
Aneuploidy can cause genetic disorders, such as Down syndrome, Turner syndrome, Klinefelter syndrome, and others.
What is gene-linkage? What does indicate it?
Gene-linkage is the tendency of genes that are located close to each other on the same chromosome to be inherited together.
This means that they do not follow the Mendelian law of independent assortment, which states that genes on different chromosomes segregate randomly.
Gene-linkage can be measured by the recombination frequency, which is the proportion of offspring that show a different combination of traits from the parents.
The recombination frequency depends on the distance between the genes: the closer the genes are, the lower the recombination frequency, and vice versa.
What is a crossing over/chiasma? What are its roles in meiosis?
Crossing over is the reciprocal exchange of genetic material between homologous chromosomes during meiosis.
A chiasma is the point where two homologous chromosomes are physically connected by crossing over.
Crossing over and chiasma have two main roles in meiosis: they ensure the proper segregation of homologous chromosomes, and they increase the genetic diversity of the gametes by creating new combinations of alleles.
What does determine gene segregation and genetic diversity?
Gene segregation is the separation of alleles of the same gene into different gametes during meiosis.
Gene segregation follows the Mendelian law of segregation, which states that each gamete receives only one allele of each gene.
Gene segregation contributes to genetic diversity by allowing different combinations of alleles to be inherited by the offspring.
Genetic diversity is also influenced by other factors, such as independent assortment, recombination, fertilization, and mutations.
How is sex determined in Drosophila melanogaster? How was it demonstrated?
Sex determination in Drosophila melanogaster is based on the ratio of X chromosomes to autosomes (non-sex chromosomes)10. A ratio of 1 or more (such as XX/AA or XXY/AA) results in a female, while a ratio of 0.5 or less (such as XY/AA or X/AA) results in a male. The presence or absence of the Y chromosome does not affect the sex determination, but it affects the fertility of the male. This was demonstrated by Morgan and his colleagues by performing crosses between flies with different sex chromosomes and observing the phenotypes and genotypes of the offspring.
How is sex determined in human? How was is demonstrated?
Sex determination in human is based on the presence or absence of the Y chromosome11. The Y chromosome carries the SRY gene, which is required to develop testes and male characteristics. An individual with a Y chromosome (such as XY or XYY) is male, while an individual without a Y chromosome (such as XX or XO) is female12. The number of X chromosomes does not affect the sex determination, but it affects the development and fertility of the individual. This was demonstrated by studying the karyotypes and phenotypes of individuals with different sex chromosome abnormalities, such as Turner syndrome, Klinefelter syndrome, Swyer syndrome, and sex reversal syndrome.
How is sex determined in the animal world? Make examples.
Sex determination in the animal world can vary depending on the species and the environmental factors13. Some examples are:
Male heterogamety: The sex of the offspring is determined by the type of sperm that fertilizes the egg. This is the case for mammals, fruit flies, and some plants. The male produces two types of gametes: X-bearing and Y-bearing. The female produces only one type of gamete: X-bearing. If an X-bearing sperm fertilizes an X-bearing egg, the offspring is female (XX). If a Y-bearing sperm fertilizes an X-bearing egg, the offspring is male (XY).
Female heterogamety: The sex of the offspring is determined by the type of egg that is fertilized by the sperm. This is the case for birds, butterflies, and some reptiles. The female produces two types of gametes: Z-bearing and W-bearing. The male produces only one type of gamete: Z-bearing. If a Z-bearing sperm fertilizes a Z-bearing egg, the offspring is male (ZZ). If a Z-bearing sperm fertilizes a W-bearing egg, the offspring is female (ZW).
Temperature-dependent sex determination: The sex of the offspring is determined by the temperature of the environment during a critical period of development. This is the case for some reptiles, such as alligators, turtles, and lizards. The temperature can affect the expression of genes that are involved in sex differentiation. For example, in alligators, high temperature produces males, while low temperature produces females.
Social or environmental sex determination: The sex of the offspring is determined by the social or environmental cues that influence the hormonal or genetic regulation of sex differentiation. This is the case for some fish, worms, and crustaceans. The social or environmental factors can include the presence or absence of a mate, the population density, the day length, the food availability, and the stress level. For example, in clownfish, the largest and dominant individual in a group is female, while the others are male. If the female dies, the largest male changes sex and becomes the new female
Which genetic syndromes are associated with chromosome non-disjunction?
Chromosome non-disjunction can cause genetic syndromes that affect the health and development of the individual1415. Some examples are:
Down syndrome: It is caused by the presence of an extra copy of chromosome 21 (trisomy 21)16. It can result from non-disjunction in meiosis I or II of either parent, or from a Robertsonian translocation between chromosome 21 and another acrocentric chromosome (such as 14). It is characterized by intellectual disability, distinctive facial features, heart defects, and increased risk of leukemia and Alzheimer’s disease.
Patau syndrome: It is caused by the presence of an extra copy of chromosome 13 (trisomy 13). It can result from non-disjunction in meiosis I or II of either parent, or from a translocation involving chromosome 13. It is characterized by severe birth defects, such as cleft lip and palate, polydactyly, microcephaly, and heart anomalies. Most infants die within the first year of life.
Edwards syndrome: It is caused by the presence of an extra copy of chromosome 18 (trisomy 18). It can result from non-disjunction in meiosis I or II of either parent, or from a translocation involving chromosome 18. It is characterized by growth retardation, low birth weight, clenched fists, rocker-bottom feet, and heart defects. Most infants die within the first month of life17.
Which genetic syndromes are associated with the sex chromosome non-disjunction?
Sex chromosome non-disjunction can cause genetic syndromes that affect the sex development and fertility of the individual1514. Some examples are:
Turner syndrome: It is caused by the absence of one X chromosome in females (45,X or XO). It can result from non-disjunction in meiosis I or II of either parent, or from a deletion or translocation involving the X chromosome. It is characterized by short stature, webbed neck, underdeveloped ovaries, and heart and kidney problems. Most affected individuals are sterile.
Klinefelter syndrome: It is caused by the presence of one or more extra X chromosomes in males (47,XXY or XXY; 48,XXXY or XXYY; etc.). It can result from non-disjunction in meiosis I or II of either parent, or from a translocation involving the X or Y chromosome. It is characterized by tall and thin stature, small testes, gynecomastia, and reduced fertility. Some affected individuals may have learning difficulties or behavioral problems.Triple X syndrome: It is caused by the presence of one or more extra X chromosomes in females (47,XXX or XXX; 48,XXXX or XXXX; etc.). It can result from non-disjunction in meiosis I or II of either parent, or from a translocation involving the X chromosome. It is characterized by tall stature, learning difficulties, and behavioral problems. Most affected individuals have normal sexual development and fertility.
XYY syndrome: It is caused by the presence of an extra Y chromosome in males (47,XYY or XYY). It can result from non-disjunction in meiosis II of the father, or from a translocation involving the Y chromosome. It is characterized by tall stature, acne, and speech and language delays. Most affected individuals have normal sexual development and fertility.
What are the genetic causes of Down syndrome? Draw representative pedigree/s
Down syndrome: Down syndrome is caused by the presence of an extra copy of chromosome 21 (trisomy 21). This can occur due to non-disjunction during meiosis in the mother, leading to an egg with two copies of chromosome 21. When this egg is fertilized by a sperm with a normal set of chromosomes, the resulting embryo has three copies of chromosome 21. The representative pedigree would show that the parents are usually normal, but their child has Down syndrome.
What are the characteristics of a sex-linked disease? Draw a representative pedigree/s
Sex-linked disease: A sex-linked disease is a disease that is caused by a gene on the sex chromosomes, usually the X chromosome. This means that males (XY) are more likely to be affected than females (XX), because males have only one X chromosome and therefore have only one copy of the gene. A representative pedigree would show that the disease is passed from an affected father to all his daughters (who are carriers), but not to his sons, and from a carrier mother to half of her sons (who are affected) and half of her daughters (who are carriers).
