HideShow resource information
  • Created by: Hindleyc
  • Created on: 23-06-18 15:43
What is Sexual reproduction?
Production of offspring from 2 parents using gametes
1 of 42
What do cells of offspring have?
2 sets of chromosomes (one from each parent cell)- diploid
2 of 42
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
3 of 42
What does a Human somatic (body) cell contain?
46 Chromosomes that consist of 23 pairs of homologous chromosomes
4 of 42
What does each pair contain?
One chromosomes from each parent (other species have diff numbers of these homologous pairs)
5 of 42
What do Sex cells or gametes have?
Only one copy of each chromosome- they are haploid
6 of 42
what is a somatic cell?
Contains 2 of each and is called diploid
7 of 42
How are chromosomes arranged ?
In pairs
8 of 42
What are members of each pair?
Same size and shape and carry genes controlling same characteristics in same order
9 of 42
Members of each pair make up
Homologous chromosomes
10 of 42
Where do you inherit one member of each pair from?
from mother- maternal C and one from father- paternal chromosome
11 of 42
What is a cell with pairs of homologous chromosomes?
Diploid (2n)
12 of 42
What is a cell with only one chromosome from each homologous pair?
Haploid (n)
13 of 42
What are all somatic cells in a multicellular organism?
Genetically identical as a result of mitosis
14 of 42
What did they all depend from
A zygote- single cell formed when 2 haploid gametes fuse
15 of 42
What are Gametes?
Genetically unique because unlike somatic cells they were formed by meiosis
16 of 42
What is Meiosis
Process of cell division underlying sexual reproduction - is a 2 step process
17 of 42
What does Meiosis 1 do
Introduces genetic diversity by randomly dividing a cells genes in two- results in 2 haploid cells
18 of 42
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
19 of 42
What does random fertilisation of gametes increase?
Genetic diversity as gametes all have varied genetic content so combining gametes increases diversity of gene distribution
20 of 42
How does it start?
With DNA replication like mitosis
21 of 42
What does it proceed with? what does this produce?
2 Divisions- 4 daughter cells
22 of 42
What happens to chromosome number
Halved from diploid number 2n to haploid number n- reductive division
23 of 42
Why is this necessary?
So chromosome number remains constant from generation to generation
24 of 42
What happens to chromosomes
Re-arragned during meiosis to form new combinations of genes
25 of 42
What is this genetic recombination?
Vitally important and is major source of genetic variation eg all sperm different
26 of 42
Before first meiotic division?
Pairs of homologous chromosomes- cells with diploid number 4 (2 pairs of homologous chromosomes)
27 of 42
After first meiotic division
Each cells has the haploid number of chromosomes but is not a truly haploid cell
28 of 42
What happens after second division
Four haploid cells containing one member from each homologous pair of chromosomes
29 of 42
what creates genetic diversity within a population
Sexual reproduction
30 of 42
what is this vital for
Species' survival
31 of 42
What are the 2 processed during meiosis that determine the unique make up of the four daughter cells
Crossing over and Independent assortement
32 of 42
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
33 of 42
What is independent assortment
Chromosomes from each pair are randomly allowed to daughter cells by independent assortment
34 of 42
what do homologous chromosomes carry
Genes controlling same characteristics in same order
35 of 42
What each gene have?
Different forms called Alleles eg Hb 2 forms 1 for Sickle cell and 1 not
36 of 42
What do Maternal and Paternal chromosomes in one HP carry
Different alleles of many of their genes
37 of 42
What does independent assortment. therefore produce
Different combinations of genes in the cells formed during meiosis
38 of 42
What is Non-disjunction
During meiosis when 2 homologous chromosomes, instead of separating both go into the same gamete
39 of 42
What happens as a result of non-disjunction
Some gametes have 2 copies of a chromosome and others lack a copy
40 of 42
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
41 of 42
What is a Karyotype
Full set of chromosomes of an individual arranged in sequence
42 of 42

Other cards in this set

Card 2


What do cells of offspring have?


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

Card 3


What are the 2 stages of sexual reproduction


Preview of the front of card 3

Card 4


What does a Human somatic (body) cell contain?


Preview of the front of card 4

Card 5


What does each pair contain?


Preview of the front of card 5
View more cards


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all DNA, genetics and evolution resources »