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02:32X and Y Chromosomes
Among mammals, the gender of an organism is determined by the sex chromosomes. Humans have two sex chromosomes, X and Y. Every human diploid cell has 22 pairs of autosomes and one pair of sex chromosomes. A human female has two X chromosomes, while a male has one X chromosome and one Y chromosome.
The germline cells such as egg and sperm cells carry only half the number of chromosomes, i.e., 22 autosomes and one sex chromosome. All eggs have an X chromosome, while sperm cells can carry an X or...
The germline cells such as egg and sperm cells carry only half the number of chromosomes, i.e., 22 autosomes and one sex chromosome. All eggs have an X chromosome, while sperm cells can carry an X or...
01:39Chromosomal Theory of Inheritance
In 1866, Gregor Mendel published the results of his pea plant breeding experiments, providing evidence for predictable patterns in the inheritance of physical characteristics. The significance of his findings was not immediately recognized. In fact, the existence of genes was unknown at the time. Mendel referred to hereditary units as “factors.”
02:45The Ratio of X Chromosome to Autosomes
In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...
02:27Trihybrid Crosses
Trihybrid Crosses
Some of Mendel’s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A trihybrid cross is a combination of three individual monohybrid crosses. For example, plant height (tall vs. short), seed shape (round vs. wrinkled), and seed color (yellow vs. green).
The F1 generation plants of a trihybrid cross are heterozygous for all three traits and produce eight gametes. Upon self-fertilization, these gametes have an equal chance to...
Some of Mendel’s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A trihybrid cross is a combination of three individual monohybrid crosses. For example, plant height (tall vs. short), seed shape (round vs. wrinkled), and seed color (yellow vs. green).
The F1 generation plants of a trihybrid cross are heterozygous for all three traits and produce eight gametes. Upon self-fertilization, these gametes have an equal chance to...
01:49Law of Segregation
When crossing pea plants, Mendel noticed that one of the parental traits would sometimes disappear in the first generation of offspring, called the F1 generation, and could reappear in the next generation (F2). He concluded that one of the traits must be dominant over the other, thereby causing masking of one trait in the F1 generation. When he crossed the F1 plants, he found that 75% of the offspring in the F2 generation had the dominant phenotype, while 25% had the recessive phenotype.
01:43Incomplete Dominance
Gregor Mendel's work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid cell has two variants called alleles inherited from each parent. He suggested that amongst these two alleles, one allele is dominant in character and the other recessive. The combination of alleles determines the phenotype of a gene in an organism.
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Plant sex chromosomes.
1Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Ashworth Lab. King's Buildings, Edinburgh, UK.
Genome Dynamics
|August 30, 2008
Summary
Dioecious plants possess sex chromosomes, similar to animals. Studies on Silene latifolia reveal that male-specific Y (MSY) regions evolve uniquely, with recombination cessation leading to distinct genetic landscapes and potential gene loss over time.
Area of Science:
- Plant genetics
- Evolutionary biology
- Sex chromosome evolution
Background:
- Dioecious plants, like some animals, exhibit distinguishable sex chromosomes.
- Male-specific Y (MSY) regions in plants prevent genetic recombination, leading to divergence from X chromosomes.
- Previous research indicates varying cessation times of recombination across different genes in Silene latifolia.
Purpose of the Study:
- To investigate the evolutionary dynamics of male-specific Y (MSY) regions in plants.
- To understand the patterns of sequence divergence and recombination suppression between X and Y chromosomes.
- To explore the predicted accumulation of repetitive sequences and gene density changes in MSY regions.
Main Methods:
- Analysis of genetic maps to identify sex-determining regions.
Main Results:
- Recombination between X and Y chromosomes in Silene latifolia ceased at different times for various genes.
- MSY regions are predicted to accumulate repetitive sequences and exhibit low gene density, a phenomenon observed in papaya but not yet widely documented in other plants.
- Available data suggest many plant MSY genes remain functional, possibly due to slow degeneration of male gametophyte genes.
Conclusions:
- The evolution of plant sex chromosomes is characterized by differential recombination suppression and sequence divergence.
- MSY regions in plants are expected to undergo significant genomic changes, including repetitive sequence accumulation and reduced gene density.
- Further research on sex-linked genes is crucial to understand deleterious mutation accumulation in Y genes and the origins of plant sex chromosomes.