Biology by Bradford
5.2.ARandom orientation at metaphase I
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5.2 Meiosis and Genetic Diversity: revision map
The subtopic in the middle and four tasks round it: label a diagram, complete a table and fill 8 gaps. Every box rests on a learning objective of the topic in the AP Biology course and exam description. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
Meiosis and Genetic Diversity
AP Biology · Unit 5 HeredityHover over a box to see it. Untick it to leave it off this sheet and its printout.
Name5.2.AHow many combinations?
With n pairs of chromosomes, independent assortment alone can give 2ⁿ different gametes. A human has 23 pairs, so one person can make about different gametes, before crossing over adds more. Two parents give over 70 trillion combinations of chromosomes, so siblings other than identical twins are never genetically the same. This variation gives a population the raw material for natural selection.
Topic 5.2Meiosis and Genetic Diversity
5.2.AThree sources of variation
| Source | When | Effect |
|---|---|---|
| prophase I | exchanges alleles between homologs, making new combinations on one chromosome | |
| metaphase I | each homologous pair lines up at random, so alleles on different chromosomes are shuffled | |
| Random fertilization | when gametes fuse | any sperm can fuse with any egg |
5.2.AWhen meiosis goes wrong
If homologous chromosomes or sister chromatids fail to separate, a failure called , some gametes have an extra chromosome and some have none. If an egg with an extra copy of chromosome 21 is fertilized, the zygote has three copies and develops Down syndrome (trisomy 21). Most other changes in chromosome number are lethal early in development.
Word bank 8 millionCrossing overhomologous pairindependent assortmentIndependent assortmentmetaphase platenondisjunctionspindle fiber
Answer key
Every box on the sheet with its gaps filled in, as the subtopic reads in full.
LabelRandom orientation at metaphase I
- spindle fiber
- metaphase plate
- homologous pair
- independent assortment
TableThree sources of variation
Source When Effect Crossing over prophase I exchanges alleles between homologs, making new combinations on one chromosome Independent assortment metaphase I each homologous pair lines up at random, so alleles on different chromosomes are shuffled Random fertilization when gametes fuse any sperm can fuse with any egg GapsHow many combinations?
With n pairs of chromosomes, independent assortment alone can give 2ⁿ different gametes. A human has 23 pairs, so one person can make about 8 million different gametes, before crossing over adds more. Two parents give over 70 trillion combinations of chromosomes, so siblings other than identical twins are never genetically the same. This variation gives a population the raw material for natural selection.
GapsWhen meiosis goes wrong
If homologous chromosomes or sister chromatids fail to separate, a failure called nondisjunction, some gametes have an extra chromosome and some have none. If an egg with an extra copy of chromosome 21 is fertilized, the zygote has three copies and develops Down syndrome (trisomy 21). Most other changes in chromosome number are lethal early in development.