Segments of non-sister chromatids break and reattach to the other chromatid — what is this?
Crossing over: homologous chromosomes exchange matching DNA at the same locus during prophase I.
What is the last source of variation
Random fertilization
What is nondisjunction?
When homologous chromosomes or sister chromatids fail to separate during anaphase I or II.
What happens to the daughter cells in nondisjunction?
One daughter cell gets an extra chromosome, and the other is missing one.
Why is nondisjunction a problem?
Cells end up with too much or too little genetic information, which can cause disorders.
What gametes can nondisjunction produce?
Gametes with 22 chromosomes or gametes with 24 chromosomes.
What happens when a zygote with an abnormal chromosome number divides?
Every cell in the body will contain the same abnormal chromosome number.
What is monosomy?
A condition where a cell has 45 chromosomes instead of 46 because one chromosome is missing. This leads to an incomplete homologous pair.
What is monosomy?
A condition where a cell has 45 chromosomes instead of 46 because one chromosome is missing. This leads to an incomplete homologous pair.
Example of monosomy?
Turner syndrome (Monosomy X) — individuals have only one X chromosome instead of two sex chromosomes.
What is trisomy?
The presence of 3 homologous chromosomes in each cell instead of the normal pair.
Example of a trisomy disorder?
Trisomy 21, also known as Down syndrome.
What does a zygote with trisomy contain?
It contains 47 chromosomes (not 46), meaning one set has three chromosomes instead of two.
What process produces gametes in males?
Spermatogenesis — the meiosis process that forms sperm.
What gamete is produced in males and where?
Sperm, produced in the testes.
What process produces gametes in females?
Oogenesis — the meiosis process that forms egg cells.
What gamete is produced in females and where?
Eggs (ova), produced in the ovaries.
What are identical (monozygotic) twins?
Twins that originate from a single zygote that splits into two embryos.
How do identical twins form?
During early mitosis, one cell breaks away and develops into a second embryo with identical DNA.
What are fraternal (dizygotic) twins?
Twins that come from two different eggs fertilized by two different sperm.
Do fraternal twins share DNA?
No — they share the womb, but their genes are different, like regular siblings.
Main difference between identical and fraternal twins?
Identical twins share 100% of DNA; fraternal twins share about 50%, like normal siblings.
Do fraternal twins share DNA?
No — they share the womb, but their genes are different, like regular siblings.
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Unit A Part 141
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Unit A part 257
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Unit A part 321
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Unit A part 4 (eye)47
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Unit A Prt 5 (ear)51
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Unit A(2) Part 1 Endocrine System43
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Unit A (2) Part 235
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Unit B Reproduction47
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Unit B Reproduction Part 260
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Unit B Part 352
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Unit C Molecular Biology44
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Unit C Molecular Biology Part 245
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Unit C Molecular Bio Part 319
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Unit C2 Part1 molecular bio44
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UNIT C2 part 256
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Unit C2 Part 323
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Unit C22 Patterns And Processes47
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Unit C22 Part 249
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Unit C22 Part 335
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Unit D Population Dynamics46
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Unit D population dynamics part 250
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Unit D Part 317
