Podcast
Questions and Answers
What unique feature does the X chromosome have compared to the Y chromosome in humans?
What unique feature does the X chromosome have compared to the Y chromosome in humans?
- It is smaller and carries fewer genes.
- It is larger and carries more genes. (correct)
- It has more linked genes than the Y chromosome.
- It contains only sex-linked disorders.
What is the term used for the inactive X chromosome in female mammals?
What is the term used for the inactive X chromosome in female mammals?
- Genomic imprint
- Gene body
- Linkage group
- Barr body (correct)
Which of the following best describes why color blindness is more common in males?
Which of the following best describes why color blindness is more common in males?
- Color blindness is caused by a dominant trait.
- Males have a higher number of X-linked genes.
- Males have only one X chromosome, making them hemizygous. (correct)
- Females can easily mask the trait with a second X chromosome. (correct)
What does genetic recombination result in following the inheritance of linked genes?
What does genetic recombination result in following the inheritance of linked genes?
Which scenario correctly identifies when a female expresses a recessive sex-linked trait?
Which scenario correctly identifies when a female expresses a recessive sex-linked trait?
In the context of sex-linked traits, what characterizes females as mosaics?
In the context of sex-linked traits, what characterizes females as mosaics?
What is the expected ratio of XX to XY progeny in random fertilization?
What is the expected ratio of XX to XY progeny in random fertilization?
Which of the following statements regarding linked genes is true?
Which of the following statements regarding linked genes is true?
Flashcards
Sex Chromosomes
Sex Chromosomes
Chromosomes that determine sex, typically X and Y in humans.
Sex-linked traits
Sex-linked traits
Traits controlled by genes located on the sex chromosomes (X or Y).
Y-linked traits
Y-linked traits
Traits caused by genes only found on the Y chromosome in humans.
X-linked recessive disorders
X-linked recessive disorders
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X inactivation
X inactivation
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Linked Genes
Linked Genes
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Genetic Recombination
Genetic Recombination
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Sex determination in humans
Sex determination in humans
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Study Notes
Human Sex Chromosomes
- A small region of homology between sex chromosomes allows them to pair up and segregate during meiosis I.
- This contributes to the pattern of sex-linked traits.
- The X and Y chromosomes share a small region of homology.
- Very few genes on the X chromosome have counterparts on the Y chromosome.
- Random fertilization produces a 1:1 ratio of XX and XY progeny, but a slight excess of males is observed at birth.
Segregation of Sex Chromosomes
- Random fertilization produces a 1:1 ratio of XX and XY offspring.
- Sex ratios show a slight male excess.
Sex-Linked Genes
- Sex-linked genes are found only on sex chromosomes.
- Sex determination varies between species.
- In humans, females are XX and males are XY.
- The X chromosome is larger and contains more genes than the Y chromosome.
- Genes only found on the X chromosome are called X-linked genes.
Inheritance Patterns of Sex-Linked Traits
- Recessive sex-linked traits require two copies of the allele in females (homozygous) and one copy in males (hemizygous) to be expressed.
Sex-Linked Disorders
- X-linked recessive disorders are more common in males than females.
- Examples include color blindness and hemophilia.
X Inactivation in Females
- In each mammalian female cell, one of the two X chromosomes is randomly inactivated during development.
- The inactivated chromosome condenses into a Barr body.
- If a female is heterozygous for a gene on the X chromosome, she will be a mosaic for that trait.
- The mosaicism is clearly visible in calico cats.
Linked Genes
- A chromosome contains hundreds or thousands of genes.
- Genes located on the same chromosome are linked genes.
- Linked genes tend to be inherited together.
- Morgan used fruit flies to study how linkage affects inheritance of two traits.
Morgan's Experiment
- Morgan crossed fruit flies that differed in body color and wing size.
- He observed traits inherited together, indicating linkage.
- Genes located on the same chromosome show linkage.
- Some nonparental phenotypes appear, indicating genetic recombination.
Recombination
- Parental traits are inherited together, but recombination results in new combinations of traits.
- A 50% recombination frequency is observed for genes on different chromosomes.
- A recombination frequency less than 50% indicates linkage.
- Recombination results from crossing over, the physical exchange of segments between homologous chromosomes.
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