Meiosis

  • Created by: Hindleyc
  • Created on: 23-06-18 15:43
What is Sexual reproduction?
Production of offspring from 2 parents using gametes
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What do cells of offspring have?
2 sets of chromosomes (one from each parent cell)- diploid
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What are the 2 stages of sexual reproduction
Meiosis- special cell division that makes haploid gametes and Fertilisation- fusion of 2 gametes to form a diploid zygote
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What does a Human somatic (body) cell contain?
46 Chromosomes that consist of 23 pairs of homologous chromosomes
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What does each pair contain?
One chromosomes from each parent (other species have diff numbers of these homologous pairs)
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What do Sex cells or gametes have?
Only one copy of each chromosome- they are haploid
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what is a somatic cell?
Contains 2 of each and is called diploid
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How are chromosomes arranged ?
In pairs
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What are members of each pair?
Same size and shape and carry genes controlling same characteristics in same order
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Members of each pair make up
Homologous chromosomes
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Where do you inherit one member of each pair from?
from mother- maternal C and one from father- paternal chromosome
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What is a cell with pairs of homologous chromosomes?
Diploid (2n)
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What is a cell with only one chromosome from each homologous pair?
Haploid (n)
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What are all somatic cells in a multicellular organism?
Genetically identical as a result of mitosis
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What did they all depend from
A zygote- single cell formed when 2 haploid gametes fuse
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What are Gametes?
Genetically unique because unlike somatic cells they were formed by meiosis
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What is Meiosis
Process of cell division underlying sexual reproduction - is a 2 step process
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What does Meiosis 1 do
Introduces genetic diversity by randomly dividing a cells genes in two- results in 2 haploid cells
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What is meiosis 2
Similar to mitosis as splits each chromosome into its 2 chromatids and places one in each daughter cell- results in 4 haploid gametes
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What does random fertilisation of gametes increase?
Genetic diversity as gametes all have varied genetic content so combining gametes increases diversity of gene distribution
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How does it start?
With DNA replication like mitosis
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What does it proceed with? what does this produce?
2 Divisions- 4 daughter cells
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What happens to chromosome number
Halved from diploid number 2n to haploid number n- reductive division
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Why is this necessary?
So chromosome number remains constant from generation to generation
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What happens to chromosomes
Re-arragned during meiosis to form new combinations of genes
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What is this genetic recombination?
Vitally important and is major source of genetic variation eg all sperm different
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Before first meiotic division?
Pairs of homologous chromosomes- cells with diploid number 4 (2 pairs of homologous chromosomes)
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After first meiotic division
Each cells has the haploid number of chromosomes but is not a truly haploid cell
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What happens after second division
Four haploid cells containing one member from each homologous pair of chromosomes
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what creates genetic diversity within a population
Sexual reproduction
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what is this vital for
Species' survival
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What are the 2 processed during meiosis that determine the unique make up of the four daughter cells
Crossing over and Independent assortement
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What is Crossing over
During meiosis 1 homologous pairs of chromosomes swap parts of their genetic material- called crossing over- Members of each H pair lie side by side break at same point along their length and broken segments can join other member of C pair
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What is independent assortment
Chromosomes from each pair are randomly allowed to daughter cells by independent assortment
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what do homologous chromosomes carry
Genes controlling same characteristics in same order
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What each gene have?
Different forms called Alleles eg Hb 2 forms 1 for Sickle cell and 1 not
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What do Maternal and Paternal chromosomes in one HP carry
Different alleles of many of their genes
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What does independent assortment. therefore produce
Different combinations of genes in the cells formed during meiosis
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What is Non-disjunction
During meiosis when 2 homologous chromosomes, instead of separating both go into the same gamete
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What happens as a result of non-disjunction
Some gametes have 2 copies of a chromosome and others lack a copy
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What is Downsydrome
In humans if an Ovum (egg cell) with 2 copies of chromosome 21 is fertilised by normal sperm cell then individual formed has 3 copies of chromosome 21 in their cells
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What is a Karyotype
Full set of chromosomes of an individual arranged in sequence
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Other cards in this set

Card 2

Front

What do cells of offspring have?

Back

2 sets of chromosomes (one from each parent cell)- diploid

Card 3

Front

What are the 2 stages of sexual reproduction

Back

Preview of the front of card 3

Card 4

Front

What does a Human somatic (body) cell contain?

Back

Preview of the front of card 4

Card 5

Front

What does each pair contain?

Back

Preview of the front of card 5
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