Meiosis and Genetic Diversity
Introduced| English |
|---|
| crossing over/ˈkrɒsɪŋ ˈəʊvə/ |
| independent assortment/ˌɪndɪˈpendənt əˈsɔːtmənt/ |
| genetic diversity/dʒɪˈnetɪk daɪˈvɜːsɪti/ |
Why no two siblings are the same
- Brothers and sisters share the same parents, yet all look different.
- Sexual reproduction shuffles genes into brand-new combinations every time.
- Meiosis is where most of that shuffling happens.
- This variety is one of biology's greatest advantages.
Crossing over
- During meiosis, matching chromosomes pair up closely.
- In crossing over 交叉互换, they swap sections of DNA.
- This mixes the mother's and father's genes on a single chromosome.
- Each chromosome that results is a new blend, unlike either parent's.
In crossing over, what happens?
In crossing over, homologous chromosomes exchange matching sections, creating new gene combinations.
Independent assortment
- Each pair of chromosomes lines up randomly before separating.
- This is independent assortment 自由组合.
- So each gamete gets a random mix of maternal and paternal chromosomes.
- With 23 pairs, that alone gives millions of possible combinations.
Where variation comes from
Step through the ways meiosis and fertilization shuffle genes into new combinations.
Independent assortment means…
Independent assortment: each pair orients randomly, so gametes get random mixes of maternal and paternal chromosomes.
Random fertilization
- Any one of millions of sperm can fertilise the egg.
- This is random fertilization, multiplying the diversity again.
- Together, these three sources make each offspring genetically unique.
- All of this variety is the raw material for genetic diversity 遗传多样性.
Genetic diversity helps a population survive changing conditions.
Variety means some individuals may cope with a new challenge — the raw material for evolution.
The random joining of any sperm with any egg is called random ____.
Random fertilization multiplies the diversity already created within meiosis.
Select all sources of genetic diversity.
Cloning produces no diversity. The other three all shuffle genes into new combinations.
Sexual reproduction creates diversity; asexual reproduction does not. A cell dividing by mitosis makes identical clones. Only meiosis, with crossing over and independent assortment, shuffles the genes to make every offspring different.
Why a family is full of variety:
- Crossing over remixes each parent's chromosomes.
- Independent assortment deals each gamete a random hand of chromosomes.
- Random fertilization then pairs two unique gametes — so each child is a fresh combination, never seen before.
Meiosis creates genetic diversity through three shuffling steps: crossing over (matching chromosomes swap sections), independent assortment (pairs line up randomly), and random fertilization (any sperm meets any egg). Together they make every offspring genetically unique — the raw material for evolution.